Function miqMenuChangeRow
has 65 lines of code (exceeds 25 allowed). Consider refactoring. Open
window.miqMenuChangeRow = function(action, elem) {
var grid = $('#folder_grid .panel-group');
var selected = grid.find('.panel-heading.active').parent();
switch (action) {
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Function miqTreeClearState
has a Cognitive Complexity of 9 (exceeds 5 allowed). Consider refactoring. Open
window.miqTreeClearState = function(tree) {
if (tree === undefined) {
// Clear all tree state objects
var to_remove = [];
for (var i = 0; i < sessionStorage.length; i++) {
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Cognitive Complexity
Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.
A method's cognitive complexity is based on a few simple rules:
- Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
- Code is considered more complex for each "break in the linear flow of the code"
- Code is considered more complex when "flow breaking structures are nested"
Further reading
Function miqMenuChangeRow
has a Cognitive Complexity of 9 (exceeds 5 allowed). Consider refactoring. Open
window.miqMenuChangeRow = function(action, elem) {
var grid = $('#folder_grid .panel-group');
var selected = grid.find('.panel-heading.active').parent();
switch (action) {
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Cognitive Complexity
Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.
A method's cognitive complexity is based on a few simple rules:
- Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
- Code is considered more complex for each "break in the linear flow of the code"
- Code is considered more complex when "flow breaking structures are nested"
Further reading
Function miqTreeScrollToNode
has a Cognitive Complexity of 6 (exceeds 5 allowed). Consider refactoring. Open
window.miqTreeScrollToNode = function(tree, id) {
var node = miqTreeFindNodeByKey(tree, id);
var parentPanelBody = node.$el.parents('div.panel-body');
if (parentPanelBody.length > 0) {
// Calculate the current node position relative to the scrollable panel
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Cognitive Complexity
Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.
A method's cognitive complexity is based on a few simple rules:
- Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
- Code is considered more complex for each "break in the linear flow of the code"
- Code is considered more complex when "flow breaking structures are nested"
Further reading
Unexpected var, use let or const instead. Open
var url = '/' + ManageIQ.controller + '/tree_select/?id=' + encodeURIComponent(key.split('__')[0]);
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
A space is required after '{'. Open
miqJqueryRequest(url, {data: {all_checked: selectedKeys}});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
obj = $('#' + tree + 'box').treeview(true);
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Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
A space is required after '{'. Open
ManageIQ.redux.store.dispatch({namespace: tree, type: '@@tree/selectNode', key: key});
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
A space is required after '{'. Open
ManageIQ.redux.store.dispatch({namespace: tree, type: '@@tree/expandNode', key: key});
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
All 'var' declarations must be at the top of the function scope. Open
var nodePos = node.$el.offset().top - parentPanelBody.offset().top;
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Require Variable Declarations to be at the top of their scope (vars-on-top)
The vars-on-top
rule generates warnings when variable declarations are not used serially at the top of a function scope or the top of a program.
By default variable declarations are always moved (“hoisted”) invisibly to the top of their containing scope by the JavaScript interpreter.
This rule forces the programmer to represent that behavior by manually moving the variable declaration to the top of its containing scope.
Rule Details
This rule aims to keep all variable declarations in the leading series of statements. Allowing multiple declarations helps promote maintainability and is thus allowed.
Examples of incorrect code for this rule:
/*eslint vars-on-top: "error"*/
// Variable declarations in a block:
function doSomething() {
var first;
if (true) {
first = true;
}
var second;
}
// Variable declaration in for initializer:
function doSomething() {
for (var i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
// Variables after other statements:
f();
var a;
Examples of correct code for this rule:
/*eslint vars-on-top: "error"*/
function doSomething() {
var first;
var second; //multiple declarations are allowed at the top
if (true) {
first = true;
}
}
function doSomething() {
var i;
for (i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
var a;
f();
/*eslint vars-on-top: "error"*/
// Directives may precede variable declarations.
"use strict";
var a;
f();
// Comments can describe variables.
function doSomething() {
// this is the first var.
var first;
// this is the second var.
var second
}
Further Reading
A space is required before '}'. Open
parentPanelBody.animate({scrollTop: parentPanelBody.scrollTop() + offset});
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Missing semicolon. Open
}
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
All 'var' declarations must be at the top of the function scope. Open
for (var property in tree) {
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Require Variable Declarations to be at the top of their scope (vars-on-top)
The vars-on-top
rule generates warnings when variable declarations are not used serially at the top of a function scope or the top of a program.
By default variable declarations are always moved (“hoisted”) invisibly to the top of their containing scope by the JavaScript interpreter.
This rule forces the programmer to represent that behavior by manually moving the variable declaration to the top of its containing scope.
Rule Details
This rule aims to keep all variable declarations in the leading series of statements. Allowing multiple declarations helps promote maintainability and is thus allowed.
Examples of incorrect code for this rule:
/*eslint vars-on-top: "error"*/
// Variable declarations in a block:
function doSomething() {
var first;
if (true) {
first = true;
}
var second;
}
// Variable declaration in for initializer:
function doSomething() {
for (var i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
// Variables after other statements:
f();
var a;
Examples of correct code for this rule:
/*eslint vars-on-top: "error"*/
function doSomething() {
var first;
var second; //multiple declarations are allowed at the top
if (true) {
first = true;
}
}
function doSomething() {
var i;
for (i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
var a;
f();
/*eslint vars-on-top: "error"*/
// Directives may precede variable declarations.
"use strict";
var a;
f();
// Comments can describe variables.
function doSomething() {
// this is the first var.
var first;
// this is the second var.
var second
}
Further Reading
Unexpected string concatenation. Open
DoNav('/vm_or_template/show/' + encodeURIComponent(nid[1]));
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Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
A space is required after '{'. Open
miqJqueryRequest('/' + ManageIQ.controller + '/tree_select/?id=' + encodeURIComponent(id) + '&tree=' + tree, {beforeSend: true});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
A space is required after '{'. Open
ManageIQ.redux.store.dispatch({namespace: treename, type: '@@tree/expandNode', key: key});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var grid = $('#folder_grid .panel-group');
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
A space is required after '{'. Open
miqJqueryRequest('/report/menu_folder_message_display?typ=add', {no_encoding: true});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
A space is required before '}'. Open
miqJqueryRequest('/report/menu_folder_message_display?typ=add', {no_encoding: true});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
Unexpected function expression. Open
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Require using arrow functions for callbacks (prefer-arrow-callback)
Arrow functions can be an attractive alternative to function expressions for callbacks or function arguments.
For example, arrow functions are automatically bound to their surrounding scope/context. This provides an alternative to the pre-ES6 standard of explicitly binding function expressions to achieve similar behavior.
Additionally, arrow functions are:
less verbose, and easier to reason about.
bound lexically regardless of where or when they are invoked.
Rule Details
This rule locates function expressions used as callbacks or function arguments. An error will be produced for any that could be replaced by an arrow function without changing the result.
The following examples will be flagged:
/* eslint prefer-arrow-callback: "error" */
foo(function(a) { return a; }); // ERROR
// prefer: foo(a => a)
foo(function() { return this.a; }.bind(this)); // ERROR
// prefer: foo(() => this.a)
Instances where an arrow function would not produce identical results will be ignored.
The following examples will not be flagged:
/* eslint prefer-arrow-callback: "error" */
/* eslint-env es6 */
// arrow function callback
foo(a => a); // OK
// generator as callback
foo(function*() { yield; }); // OK
// function expression not used as callback or function argument
var foo = function foo(a) { return a; }; // OK
// unbound function expression callback
foo(function() { return this.a; }); // OK
// recursive named function callback
foo(function bar(n) { return n && n + bar(n - 1); }); // OK
Options
Access further control over this rule's behavior via an options object.
Default: { allowNamedFunctions: false, allowUnboundThis: true }
allowNamedFunctions
By default { "allowNamedFunctions": false }
, this boolean
option prohibits using named functions as callbacks or function arguments.
Changing this value to true
will reverse this option's behavior by allowing use of named functions without restriction.
{ "allowNamedFunctions": true }
will not flag the following example:
/* eslint prefer-arrow-callback: [ "error", { "allowNamedFunctions": true } ] */
foo(function bar() {});
allowUnboundThis
By default { "allowUnboundThis": true }
, this boolean
option allows function expressions containing this
to be used as callbacks, as long as the function in question has not been explicitly bound.
When set to false
this option prohibits the use of function expressions as callbacks or function arguments entirely, without exception.
{ "allowUnboundThis": false }
will flag the following examples:
/* eslint prefer-arrow-callback: [ "error", { "allowUnboundThis": false } ] */
/* eslint-env es6 */
foo(function() { this.a; });
foo(function() { (() => this); });
someArray.map(function(itm) { return this.doSomething(itm); }, someObject);
When Not To Use It
In environments that have not yet adopted ES6 language features (ES3/5).
In ES6+ environments that allow the use of function expressions when describing callbacks or function arguments.
Further Reading
Missing semicolon. Open
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Missing semicolon. Open
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var url = ManageIQ.tree.checkUrl + '?id=' + encodeURIComponent(key) + '&check=' + checked;
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Missing semicolon. Open
}
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
console.error("miqTreeFindNodeByKey: tree '" + tree + "' does not exist.");
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Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
var url = '/' + ManageIQ.controller + '/tree_select/?id=' + encodeURIComponent(key.split('__')[0]);
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Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
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Require Object Literal Shorthand Syntax (object-shorthand)
ECMAScript 6 provides a concise form for defining object literal methods and properties. This syntax can make defining complex object literals much cleaner.
Here are a few common examples using the ES5 syntax:
// properties
var foo = {
x: x,
y: y,
z: z,
};
// methods
var foo = {
a: function() {},
b: function() {}
};
Now here are ES6 equivalents:
/*eslint-env es6*/
// properties
var foo = {x, y, z};
// methods
var foo = {
a() {},
b() {}
};
Rule Details
This rule enforces the use of the shorthand syntax. This applies to all methods (including generators) defined in object literals and any properties defined where the key name matches name of the assigned variable.
Each of the following properties would warn:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
w: function() {},
x: function *() {},
[y]: function() {},
z: z
};
In that case the expected syntax would have been:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
w() {},
*x() {},
[y]() {},
z
};
This rule does not flag arrow functions inside of object literals. The following will not warn:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
x: (y) => y
};
See Also:
-
no-useless-rename
which disallows renaming import, export, and destructured assignments to the same name.
Options
The rule takes an option which specifies when it should be applied. It can be set to one of the following values:
-
"always"
(default) expects that the shorthand will be used whenever possible. -
"methods"
ensures the method shorthand is used (also applies to generators). -
"properties"
ensures the property shorthand is used (where the key and variable name match). -
"never"
ensures that no property or method shorthand is used in any object literal. -
"consistent"
ensures that either all shorthand or all long-form will be used in an object literal. -
"consistent-as-needed"
ensures that either all shorthand or all long-form will be used in an object literal, but ensures all shorthand whenever possible.
You can set the option in configuration like this:
{
"object-shorthand": ["error", "always"]
}
Additionally, the rule takes an optional object configuration:
-
"avoidQuotes": true
indicates that long-form syntax is preferred whenever the object key is a string literal (default:false
). Note that this option can only be enabled when the string option is set to"always"
,"methods"
, or"properties"
. -
"ignoreConstructors": true
can be used to prevent the rule from reporting errors for constructor functions. (By default, the rule treats constructors the same way as other functions.) Note that this option can only be enabled when the string option is set to"always"
or"methods"
. -
"avoidExplicitReturnArrows": true
indicates that methods are preferred over explicit-return arrow functions for function properties. (By default, the rule allows either of these.) Note that this option can only be enabled when the string option is set to"always"
or"methods"
.
avoidQuotes
{
"object-shorthand": ["error", "always", { "avoidQuotes": true }]
}
Example of incorrect code for this rule with the "always", { "avoidQuotes": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidQuotes": true }]*/
/*eslint-env es6*/
var foo = {
"bar-baz"() {}
};
Example of correct code for this rule with the "always", { "avoidQuotes": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidQuotes": true }]*/
/*eslint-env es6*/
var foo = {
"bar-baz": function() {},
"qux": qux
};
ignoreConstructors
{
"object-shorthand": ["error", "always", { "ignoreConstructors": true }]
}
Example of correct code for this rule with the "always", { "ignoreConstructors": true }
option:
/*eslint object-shorthand: ["error", "always", { "ignoreConstructors": true }]*/
/*eslint-env es6*/
var foo = {
ConstructorFunction: function() {}
};
avoidExplicitReturnArrows
{
"object-shorthand": ["error", "always", { "avoidExplicitReturnArrows": true }]
}
Example of incorrect code for this rule with the "always", { "avoidExplicitReturnArrows": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidExplicitReturnArrows": true }]*/
/*eslint-env es6*/
var foo = {
foo: (bar, baz) => {
return bar + baz;
},
qux: (foobar) => {
return foobar * 2;
}
};
Example of correct code for this rule with the "always", { "avoidExplicitReturnArrows": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidExplicitReturnArrows": true }]*/
/*eslint-env es6*/
var foo = {
foo(bar, baz) {
return bar + baz;
},
qux: foobar => foobar * 2
};
Example of incorrect code for this rule with the "consistent"
option:
/*eslint object-shorthand: [2, "consistent"]*/
/*eslint-env es6*/
var foo = {
a,
b: "foo",
};
Examples of correct code for this rule with the "consistent"
option:
/*eslint object-shorthand: [2, "consistent"]*/
/*eslint-env es6*/
var foo = {
a: a,
b: "foo"
};
var bar = {
a,
b,
};
Example of incorrect code with the "consistent-as-needed"
option, which is very similar to "consistent"
:
/*eslint object-shorthand: [2, "consistent-as-needed"]*/
/*eslint-env es6*/
var foo = {
a: a,
b: b,
};
When Not To Use It
Anyone not yet in an ES6 environment would not want to apply this rule. Others may find the terseness of the shorthand syntax harder to read and may not want to encourage it with this rule.
Further Reading
Object initializer - MDN Source: http://eslint.org/docs/rules/
Missing semicolon. Open
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
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Require Object Literal Shorthand Syntax (object-shorthand)
ECMAScript 6 provides a concise form for defining object literal methods and properties. This syntax can make defining complex object literals much cleaner.
Here are a few common examples using the ES5 syntax:
// properties
var foo = {
x: x,
y: y,
z: z,
};
// methods
var foo = {
a: function() {},
b: function() {}
};
Now here are ES6 equivalents:
/*eslint-env es6*/
// properties
var foo = {x, y, z};
// methods
var foo = {
a() {},
b() {}
};
Rule Details
This rule enforces the use of the shorthand syntax. This applies to all methods (including generators) defined in object literals and any properties defined where the key name matches name of the assigned variable.
Each of the following properties would warn:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
w: function() {},
x: function *() {},
[y]: function() {},
z: z
};
In that case the expected syntax would have been:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
w() {},
*x() {},
[y]() {},
z
};
This rule does not flag arrow functions inside of object literals. The following will not warn:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
x: (y) => y
};
See Also:
-
no-useless-rename
which disallows renaming import, export, and destructured assignments to the same name.
Options
The rule takes an option which specifies when it should be applied. It can be set to one of the following values:
-
"always"
(default) expects that the shorthand will be used whenever possible. -
"methods"
ensures the method shorthand is used (also applies to generators). -
"properties"
ensures the property shorthand is used (where the key and variable name match). -
"never"
ensures that no property or method shorthand is used in any object literal. -
"consistent"
ensures that either all shorthand or all long-form will be used in an object literal. -
"consistent-as-needed"
ensures that either all shorthand or all long-form will be used in an object literal, but ensures all shorthand whenever possible.
You can set the option in configuration like this:
{
"object-shorthand": ["error", "always"]
}
Additionally, the rule takes an optional object configuration:
-
"avoidQuotes": true
indicates that long-form syntax is preferred whenever the object key is a string literal (default:false
). Note that this option can only be enabled when the string option is set to"always"
,"methods"
, or"properties"
. -
"ignoreConstructors": true
can be used to prevent the rule from reporting errors for constructor functions. (By default, the rule treats constructors the same way as other functions.) Note that this option can only be enabled when the string option is set to"always"
or"methods"
. -
"avoidExplicitReturnArrows": true
indicates that methods are preferred over explicit-return arrow functions for function properties. (By default, the rule allows either of these.) Note that this option can only be enabled when the string option is set to"always"
or"methods"
.
avoidQuotes
{
"object-shorthand": ["error", "always", { "avoidQuotes": true }]
}
Example of incorrect code for this rule with the "always", { "avoidQuotes": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidQuotes": true }]*/
/*eslint-env es6*/
var foo = {
"bar-baz"() {}
};
Example of correct code for this rule with the "always", { "avoidQuotes": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidQuotes": true }]*/
/*eslint-env es6*/
var foo = {
"bar-baz": function() {},
"qux": qux
};
ignoreConstructors
{
"object-shorthand": ["error", "always", { "ignoreConstructors": true }]
}
Example of correct code for this rule with the "always", { "ignoreConstructors": true }
option:
/*eslint object-shorthand: ["error", "always", { "ignoreConstructors": true }]*/
/*eslint-env es6*/
var foo = {
ConstructorFunction: function() {}
};
avoidExplicitReturnArrows
{
"object-shorthand": ["error", "always", { "avoidExplicitReturnArrows": true }]
}
Example of incorrect code for this rule with the "always", { "avoidExplicitReturnArrows": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidExplicitReturnArrows": true }]*/
/*eslint-env es6*/
var foo = {
foo: (bar, baz) => {
return bar + baz;
},
qux: (foobar) => {
return foobar * 2;
}
};
Example of correct code for this rule with the "always", { "avoidExplicitReturnArrows": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidExplicitReturnArrows": true }]*/
/*eslint-env es6*/
var foo = {
foo(bar, baz) {
return bar + baz;
},
qux: foobar => foobar * 2
};
Example of incorrect code for this rule with the "consistent"
option:
/*eslint object-shorthand: [2, "consistent"]*/
/*eslint-env es6*/
var foo = {
a,
b: "foo",
};
Examples of correct code for this rule with the "consistent"
option:
/*eslint object-shorthand: [2, "consistent"]*/
/*eslint-env es6*/
var foo = {
a: a,
b: "foo"
};
var bar = {
a,
b,
};
Example of incorrect code with the "consistent-as-needed"
option, which is very similar to "consistent"
:
/*eslint object-shorthand: [2, "consistent-as-needed"]*/
/*eslint-env es6*/
var foo = {
a: a,
b: b,
};
When Not To Use It
Anyone not yet in an ES6 environment would not want to apply this rule. Others may find the terseness of the shorthand syntax harder to read and may not want to encourage it with this rule.
Further Reading
Object initializer - MDN Source: http://eslint.org/docs/rules/
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Require parens in arrow function arguments (arrow-parens)
Arrow functions can omit parentheses when they have exactly one parameter. In all other cases the parameter(s) must be wrapped in parentheses. This rule enforces the consistent use of parentheses in arrow functions.
Rule Details
This rule enforces parentheses around arrow function parameters regardless of arity. For example:
/*eslint-env es6*/
// Bad
a => {}
// Good
(a) => {}
Following this style will help you find arrow functions (=>
) which may be mistakenly included in a condition
when a comparison such as >=
was the intent.
/*eslint-env es6*/
// Bad
if (a => 2) {
}
// Good
if (a >= 2) {
}
The rule can also be configured to discourage the use of parens when they are not required:
/*eslint-env es6*/
// Bad
(a) => {}
// Good
a => {}
Options
This rule has a string option and an object one.
String options are:
-
"always"
(default) requires parens around arguments in all cases. -
"as-needed"
allows omitting parens when there is only one argument.
Object properties for variants of the "as-needed"
option:
-
"requireForBlockBody": true
modifies the as-needed rule in order to require parens if the function body is in an instructions block (surrounded by braces).
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint arrow-parens: ["error", "always"]*/
/*eslint-env es6*/
a => {};
a => a;
a => {'\n'};
a.then(foo => {});
a.then(foo => a);
a(foo => { if (true) {} });
Examples of correct code for this rule with the default "always"
option:
/*eslint arrow-parens: ["error", "always"]*/
/*eslint-env es6*/
() => {};
(a) => {};
(a) => a;
(a) => {'\n'}
a.then((foo) => {});
a.then((foo) => { if (true) {} });
If Statements
One of benefits of this option is that it prevents the incorrect use of arrow functions in conditionals:
/*eslint-env es6*/
var a = 1;
var b = 2;
// ...
if (a => b) {
console.log('bigger');
} else {
console.log('smaller');
}
// outputs 'bigger', not smaller as expected
The contents of the if
statement is an arrow function, not a comparison.
If the arrow function is intentional, it should be wrapped in parens to remove ambiguity.
/*eslint-env es6*/
var a = 1;
var b = 0;
// ...
if ((a) => b) {
console.log('truthy value returned');
} else {
console.log('falsey value returned');
}
// outputs 'truthy value returned'
The following is another example of this behavior:
/*eslint-env es6*/
var a = 1, b = 2, c = 3, d = 4;
var f = a => b ? c: d;
// f = ?
f
is an arrow function which takes a
as an argument and returns the result of b ? c: d
.
This should be rewritten like so:
/*eslint-env es6*/
var a = 1, b = 2, c = 3, d = 4;
var f = (a) => b ? c: d;
as-needed
Examples of incorrect code for this rule with the "as-needed"
option:
/*eslint arrow-parens: ["error", "as-needed"]*/
/*eslint-env es6*/
(a) => {};
(a) => a;
(a) => {'\n'};
a.then((foo) => {});
a.then((foo) => a);
a((foo) => { if (true) {} });
Examples of correct code for this rule with the "as-needed"
option:
/*eslint arrow-parens: ["error", "as-needed"]*/
/*eslint-env es6*/
() => {};
a => {};
a => a;
a => {'\n'};
a.then(foo => {});
a.then(foo => { if (true) {} });
(a, b, c) => a;
(a = 10) => a;
([a, b]) => a;
({a, b}) => a;
requireForBlockBody
Examples of incorrect code for the { "requireForBlockBody": true }
option:
/*eslint arrow-parens: [2, "as-needed", { "requireForBlockBody": true }]*/
/*eslint-env es6*/
(a) => a;
a => {};
a => {'\n'};
a.map((x) => x * x);
a.map(x => {
return x * x;
});
a.then(foo => {});
Examples of correct code for the { "requireForBlockBody": true }
option:
/*eslint arrow-parens: [2, "as-needed", { "requireForBlockBody": true }]*/
/*eslint-env es6*/
(a) => {};
(a) => {'\n'};
a => ({});
() => {};
a => a;
a.then((foo) => {});
a.then((foo) => { if (true) {} });
a((foo) => { if (true) {} });
(a, b, c) => a;
(a = 10) => a;
([a, b]) => a;
({a, b}) => a;
Further Reading
- The
"as-needed", { "requireForBlockBody": true }
rule is directly inspired by the Airbnb JS Style Guide. Source: http://eslint.org/docs/rules/
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
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Require Object Literal Shorthand Syntax (object-shorthand)
ECMAScript 6 provides a concise form for defining object literal methods and properties. This syntax can make defining complex object literals much cleaner.
Here are a few common examples using the ES5 syntax:
// properties
var foo = {
x: x,
y: y,
z: z,
};
// methods
var foo = {
a: function() {},
b: function() {}
};
Now here are ES6 equivalents:
/*eslint-env es6*/
// properties
var foo = {x, y, z};
// methods
var foo = {
a() {},
b() {}
};
Rule Details
This rule enforces the use of the shorthand syntax. This applies to all methods (including generators) defined in object literals and any properties defined where the key name matches name of the assigned variable.
Each of the following properties would warn:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
w: function() {},
x: function *() {},
[y]: function() {},
z: z
};
In that case the expected syntax would have been:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
w() {},
*x() {},
[y]() {},
z
};
This rule does not flag arrow functions inside of object literals. The following will not warn:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
x: (y) => y
};
See Also:
-
no-useless-rename
which disallows renaming import, export, and destructured assignments to the same name.
Options
The rule takes an option which specifies when it should be applied. It can be set to one of the following values:
-
"always"
(default) expects that the shorthand will be used whenever possible. -
"methods"
ensures the method shorthand is used (also applies to generators). -
"properties"
ensures the property shorthand is used (where the key and variable name match). -
"never"
ensures that no property or method shorthand is used in any object literal. -
"consistent"
ensures that either all shorthand or all long-form will be used in an object literal. -
"consistent-as-needed"
ensures that either all shorthand or all long-form will be used in an object literal, but ensures all shorthand whenever possible.
You can set the option in configuration like this:
{
"object-shorthand": ["error", "always"]
}
Additionally, the rule takes an optional object configuration:
-
"avoidQuotes": true
indicates that long-form syntax is preferred whenever the object key is a string literal (default:false
). Note that this option can only be enabled when the string option is set to"always"
,"methods"
, or"properties"
. -
"ignoreConstructors": true
can be used to prevent the rule from reporting errors for constructor functions. (By default, the rule treats constructors the same way as other functions.) Note that this option can only be enabled when the string option is set to"always"
or"methods"
. -
"avoidExplicitReturnArrows": true
indicates that methods are preferred over explicit-return arrow functions for function properties. (By default, the rule allows either of these.) Note that this option can only be enabled when the string option is set to"always"
or"methods"
.
avoidQuotes
{
"object-shorthand": ["error", "always", { "avoidQuotes": true }]
}
Example of incorrect code for this rule with the "always", { "avoidQuotes": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidQuotes": true }]*/
/*eslint-env es6*/
var foo = {
"bar-baz"() {}
};
Example of correct code for this rule with the "always", { "avoidQuotes": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidQuotes": true }]*/
/*eslint-env es6*/
var foo = {
"bar-baz": function() {},
"qux": qux
};
ignoreConstructors
{
"object-shorthand": ["error", "always", { "ignoreConstructors": true }]
}
Example of correct code for this rule with the "always", { "ignoreConstructors": true }
option:
/*eslint object-shorthand: ["error", "always", { "ignoreConstructors": true }]*/
/*eslint-env es6*/
var foo = {
ConstructorFunction: function() {}
};
avoidExplicitReturnArrows
{
"object-shorthand": ["error", "always", { "avoidExplicitReturnArrows": true }]
}
Example of incorrect code for this rule with the "always", { "avoidExplicitReturnArrows": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidExplicitReturnArrows": true }]*/
/*eslint-env es6*/
var foo = {
foo: (bar, baz) => {
return bar + baz;
},
qux: (foobar) => {
return foobar * 2;
}
};
Example of correct code for this rule with the "always", { "avoidExplicitReturnArrows": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidExplicitReturnArrows": true }]*/
/*eslint-env es6*/
var foo = {
foo(bar, baz) {
return bar + baz;
},
qux: foobar => foobar * 2
};
Example of incorrect code for this rule with the "consistent"
option:
/*eslint object-shorthand: [2, "consistent"]*/
/*eslint-env es6*/
var foo = {
a,
b: "foo",
};
Examples of correct code for this rule with the "consistent"
option:
/*eslint object-shorthand: [2, "consistent"]*/
/*eslint-env es6*/
var foo = {
a: a,
b: "foo"
};
var bar = {
a,
b,
};
Example of incorrect code with the "consistent-as-needed"
option, which is very similar to "consistent"
:
/*eslint object-shorthand: [2, "consistent-as-needed"]*/
/*eslint-env es6*/
var foo = {
a: a,
b: b,
};
When Not To Use It
Anyone not yet in an ES6 environment would not want to apply this rule. Others may find the terseness of the shorthand syntax harder to read and may not want to encourage it with this rule.
Further Reading
Object initializer - MDN Source: http://eslint.org/docs/rules/
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
All 'var' declarations must be at the top of the function scope. Open
var tree = ManageIQ.redux.store.getState()[treeName];
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Require Variable Declarations to be at the top of their scope (vars-on-top)
The vars-on-top
rule generates warnings when variable declarations are not used serially at the top of a function scope or the top of a program.
By default variable declarations are always moved (“hoisted”) invisibly to the top of their containing scope by the JavaScript interpreter.
This rule forces the programmer to represent that behavior by manually moving the variable declaration to the top of its containing scope.
Rule Details
This rule aims to keep all variable declarations in the leading series of statements. Allowing multiple declarations helps promote maintainability and is thus allowed.
Examples of incorrect code for this rule:
/*eslint vars-on-top: "error"*/
// Variable declarations in a block:
function doSomething() {
var first;
if (true) {
first = true;
}
var second;
}
// Variable declaration in for initializer:
function doSomething() {
for (var i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
// Variables after other statements:
f();
var a;
Examples of correct code for this rule:
/*eslint vars-on-top: "error"*/
function doSomething() {
var first;
var second; //multiple declarations are allowed at the top
if (true) {
first = true;
}
}
function doSomething() {
var i;
for (i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
var a;
f();
/*eslint vars-on-top: "error"*/
// Directives may precede variable declarations.
"use strict";
var a;
f();
// Comments can describe variables.
function doSomething() {
// this is the first var.
var first;
// this is the second var.
var second
}
Further Reading
A space is required after '{'. Open
miqJqueryRequest(ManageIQ.tree.clickUrl + '?id=' + encodeURIComponent(id), {beforeSend: true, complete: true});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Missing semicolon. Open
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
Missing semicolon. Open
}
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
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Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
Identifier 'to_remove' is not in camel case. Open
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Require CamelCase (camelcase)
When it comes to naming variables, style guides generally fall into one of two camps: camelcase (variableName
) and underscores (variable_name
). This rule focuses on using the camelcase approach. If your style guide calls for camelCasing your variable names, then this rule is for you!
Rule Details
This rule looks for any underscores (_
) located within the source code. It ignores leading and trailing underscores and only checks those in the middle of a variable name. If ESLint decides that the variable is a constant (all uppercase), then no warning will be thrown. Otherwise, a warning will be thrown. This rule only flags definitions and assignments but not function calls. In case of ES6 import
statements, this rule only targets the name of the variable that will be imported into the local module scope.
Options
This rule has an object option:
-
"properties": "always"
(default) enforces camelcase style for property names -
"properties": "never"
does not check property names -
"ignoreDestructuring": false
(default) enforces camelcase style for destructured identifiers -
"ignoreDestructuring": true
does not check destructured identifiers -
allow
(string[]
) list of properties to accept. Accept regex.
properties: "always"
Examples of incorrect code for this rule with the default { "properties": "always" }
option:
/*eslint camelcase: "error"*/
import { no_camelcased } from "external-module"
var my_favorite_color = "#112C85";
function do_something() {
// ...
}
obj.do_something = function() {
// ...
};
function foo({ no_camelcased }) {
// ...
};
function foo({ isCamelcased: no_camelcased }) {
// ...
}
function foo({ no_camelcased = 'default value' }) {
// ...
};
var obj = {
my_pref: 1
};
var { category_id = 1 } = query;
var { foo: no_camelcased } = bar;
var { foo: bar_baz = 1 } = quz;
Examples of correct code for this rule with the default { "properties": "always" }
option:
/*eslint camelcase: "error"*/
import { no_camelcased as camelCased } from "external-module";
var myFavoriteColor = "#112C85";
var _myFavoriteColor = "#112C85";
var myFavoriteColor_ = "#112C85";
var MY_FAVORITE_COLOR = "#112C85";
var foo = bar.baz_boom;
var foo = { qux: bar.baz_boom };
obj.do_something();
do_something();
new do_something();
var { category_id: category } = query;
function foo({ isCamelCased }) {
// ...
};
function foo({ isCamelCased: isAlsoCamelCased }) {
// ...
}
function foo({ isCamelCased = 'default value' }) {
// ...
};
var { categoryId = 1 } = query;
var { foo: isCamelCased } = bar;
var { foo: isCamelCased = 1 } = quz;
properties: "never"
Examples of correct code for this rule with the { "properties": "never" }
option:
/*eslint camelcase: ["error", {properties: "never"}]*/
var obj = {
my_pref: 1
};
ignoreDestructuring: false
Examples of incorrect code for this rule with the default { "ignoreDestructuring": false }
option:
/*eslint camelcase: "error"*/
var { category_id } = query;
var { category_id = 1 } = query;
var { category_id: category_id } = query;
var { category_id: category_alias } = query;
var { category_id: categoryId, ...other_props } = query;
ignoreDestructuring: true
Examples of incorrect code for this rule with the { "ignoreDestructuring": true }
option:
/*eslint camelcase: ["error", {ignoreDestructuring: true}]*/
var { category_id: category_alias } = query;
var { category_id, ...other_props } = query;
Examples of correct code for this rule with the { "ignoreDestructuring": true }
option:
/*eslint camelcase: ["error", {ignoreDestructuring: true}]*/
var { category_id } = query;
var { category_id = 1 } = query;
var { category_id: category_id } = query;
allow
Examples of correct code for this rule with the allow
option:
/*eslint camelcase: ["error", {allow: ["UNSAFE_componentWillMount"]}]*/
function UNSAFE_componentWillMount() {
// ...
}
/*eslint camelcase: ["error", {allow: ["^UNSAFE_"]}]*/
function UNSAFE_componentWillMount() {
// ...
}
function UNSAFE_componentWillMount() {
// ...
}
When Not To Use It
If you have established coding standards using a different naming convention (separating words with underscores), turn this rule off. Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
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Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
Missing semicolon. Open
}
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var count = grid.find('.panel-heading').length;
- Read upRead up
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- Exclude checks
require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
All 'var' declarations must be at the top of the function scope. Open
var to_remove = [];
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- Exclude checks
Require Variable Declarations to be at the top of their scope (vars-on-top)
The vars-on-top
rule generates warnings when variable declarations are not used serially at the top of a function scope or the top of a program.
By default variable declarations are always moved (“hoisted”) invisibly to the top of their containing scope by the JavaScript interpreter.
This rule forces the programmer to represent that behavior by manually moving the variable declaration to the top of its containing scope.
Rule Details
This rule aims to keep all variable declarations in the leading series of statements. Allowing multiple declarations helps promote maintainability and is thus allowed.
Examples of incorrect code for this rule:
/*eslint vars-on-top: "error"*/
// Variable declarations in a block:
function doSomething() {
var first;
if (true) {
first = true;
}
var second;
}
// Variable declaration in for initializer:
function doSomething() {
for (var i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
// Variables after other statements:
f();
var a;
Examples of correct code for this rule:
/*eslint vars-on-top: "error"*/
function doSomething() {
var first;
var second; //multiple declarations are allowed at the top
if (true) {
first = true;
}
}
function doSomething() {
var i;
for (i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
var a;
f();
/*eslint vars-on-top: "error"*/
// Directives may precede variable declarations.
"use strict";
var a;
f();
// Comments can describe variables.
function doSomething() {
// this is the first var.
var first;
// this is the second var.
var second
}
Further Reading
Missing semicolon. Open
}
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
A space is required before '}'. Open
miqJqueryRequest(url, {beforeSend: true});
- Read upRead up
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- Exclude checks
enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var node = miqTreeFindNodeByKey(tree, key);
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var node = miqTreeFindNodeByKey(tree, id);
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
A space is required after '{'. Open
parentPanelBody.animate({scrollTop: parentPanelBody.scrollTop() + offset});
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Unexpected parentheses around single function argument having a body with no curly braces. Open
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Require parens in arrow function arguments (arrow-parens)
Arrow functions can omit parentheses when they have exactly one parameter. In all other cases the parameter(s) must be wrapped in parentheses. This rule enforces the consistent use of parentheses in arrow functions.
Rule Details
This rule enforces parentheses around arrow function parameters regardless of arity. For example:
/*eslint-env es6*/
// Bad
a => {}
// Good
(a) => {}
Following this style will help you find arrow functions (=>
) which may be mistakenly included in a condition
when a comparison such as >=
was the intent.
/*eslint-env es6*/
// Bad
if (a => 2) {
}
// Good
if (a >= 2) {
}
The rule can also be configured to discourage the use of parens when they are not required:
/*eslint-env es6*/
// Bad
(a) => {}
// Good
a => {}
Options
This rule has a string option and an object one.
String options are:
-
"always"
(default) requires parens around arguments in all cases. -
"as-needed"
allows omitting parens when there is only one argument.
Object properties for variants of the "as-needed"
option:
-
"requireForBlockBody": true
modifies the as-needed rule in order to require parens if the function body is in an instructions block (surrounded by braces).
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint arrow-parens: ["error", "always"]*/
/*eslint-env es6*/
a => {};
a => a;
a => {'\n'};
a.then(foo => {});
a.then(foo => a);
a(foo => { if (true) {} });
Examples of correct code for this rule with the default "always"
option:
/*eslint arrow-parens: ["error", "always"]*/
/*eslint-env es6*/
() => {};
(a) => {};
(a) => a;
(a) => {'\n'}
a.then((foo) => {});
a.then((foo) => { if (true) {} });
If Statements
One of benefits of this option is that it prevents the incorrect use of arrow functions in conditionals:
/*eslint-env es6*/
var a = 1;
var b = 2;
// ...
if (a => b) {
console.log('bigger');
} else {
console.log('smaller');
}
// outputs 'bigger', not smaller as expected
The contents of the if
statement is an arrow function, not a comparison.
If the arrow function is intentional, it should be wrapped in parens to remove ambiguity.
/*eslint-env es6*/
var a = 1;
var b = 0;
// ...
if ((a) => b) {
console.log('truthy value returned');
} else {
console.log('falsey value returned');
}
// outputs 'truthy value returned'
The following is another example of this behavior:
/*eslint-env es6*/
var a = 1, b = 2, c = 3, d = 4;
var f = a => b ? c: d;
// f = ?
f
is an arrow function which takes a
as an argument and returns the result of b ? c: d
.
This should be rewritten like so:
/*eslint-env es6*/
var a = 1, b = 2, c = 3, d = 4;
var f = (a) => b ? c: d;
as-needed
Examples of incorrect code for this rule with the "as-needed"
option:
/*eslint arrow-parens: ["error", "as-needed"]*/
/*eslint-env es6*/
(a) => {};
(a) => a;
(a) => {'\n'};
a.then((foo) => {});
a.then((foo) => a);
a((foo) => { if (true) {} });
Examples of correct code for this rule with the "as-needed"
option:
/*eslint arrow-parens: ["error", "as-needed"]*/
/*eslint-env es6*/
() => {};
a => {};
a => a;
a => {'\n'};
a.then(foo => {});
a.then(foo => { if (true) {} });
(a, b, c) => a;
(a = 10) => a;
([a, b]) => a;
({a, b}) => a;
requireForBlockBody
Examples of incorrect code for the { "requireForBlockBody": true }
option:
/*eslint arrow-parens: [2, "as-needed", { "requireForBlockBody": true }]*/
/*eslint-env es6*/
(a) => a;
a => {};
a => {'\n'};
a.map((x) => x * x);
a.map(x => {
return x * x;
});
a.then(foo => {});
Examples of correct code for the { "requireForBlockBody": true }
option:
/*eslint arrow-parens: [2, "as-needed", { "requireForBlockBody": true }]*/
/*eslint-env es6*/
(a) => {};
(a) => {'\n'};
a => ({});
() => {};
a => a;
a.then((foo) => {});
a.then((foo) => { if (true) {} });
a((foo) => { if (true) {} });
(a, b, c) => a;
(a = 10) => a;
([a, b]) => a;
({a, b}) => a;
Further Reading
- The
"as-needed", { "requireForBlockBody": true }
rule is directly inspired by the Airbnb JS Style Guide. Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
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Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
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Require Object Literal Shorthand Syntax (object-shorthand)
ECMAScript 6 provides a concise form for defining object literal methods and properties. This syntax can make defining complex object literals much cleaner.
Here are a few common examples using the ES5 syntax:
// properties
var foo = {
x: x,
y: y,
z: z,
};
// methods
var foo = {
a: function() {},
b: function() {}
};
Now here are ES6 equivalents:
/*eslint-env es6*/
// properties
var foo = {x, y, z};
// methods
var foo = {
a() {},
b() {}
};
Rule Details
This rule enforces the use of the shorthand syntax. This applies to all methods (including generators) defined in object literals and any properties defined where the key name matches name of the assigned variable.
Each of the following properties would warn:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
w: function() {},
x: function *() {},
[y]: function() {},
z: z
};
In that case the expected syntax would have been:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
w() {},
*x() {},
[y]() {},
z
};
This rule does not flag arrow functions inside of object literals. The following will not warn:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
x: (y) => y
};
See Also:
-
no-useless-rename
which disallows renaming import, export, and destructured assignments to the same name.
Options
The rule takes an option which specifies when it should be applied. It can be set to one of the following values:
-
"always"
(default) expects that the shorthand will be used whenever possible. -
"methods"
ensures the method shorthand is used (also applies to generators). -
"properties"
ensures the property shorthand is used (where the key and variable name match). -
"never"
ensures that no property or method shorthand is used in any object literal. -
"consistent"
ensures that either all shorthand or all long-form will be used in an object literal. -
"consistent-as-needed"
ensures that either all shorthand or all long-form will be used in an object literal, but ensures all shorthand whenever possible.
You can set the option in configuration like this:
{
"object-shorthand": ["error", "always"]
}
Additionally, the rule takes an optional object configuration:
-
"avoidQuotes": true
indicates that long-form syntax is preferred whenever the object key is a string literal (default:false
). Note that this option can only be enabled when the string option is set to"always"
,"methods"
, or"properties"
. -
"ignoreConstructors": true
can be used to prevent the rule from reporting errors for constructor functions. (By default, the rule treats constructors the same way as other functions.) Note that this option can only be enabled when the string option is set to"always"
or"methods"
. -
"avoidExplicitReturnArrows": true
indicates that methods are preferred over explicit-return arrow functions for function properties. (By default, the rule allows either of these.) Note that this option can only be enabled when the string option is set to"always"
or"methods"
.
avoidQuotes
{
"object-shorthand": ["error", "always", { "avoidQuotes": true }]
}
Example of incorrect code for this rule with the "always", { "avoidQuotes": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidQuotes": true }]*/
/*eslint-env es6*/
var foo = {
"bar-baz"() {}
};
Example of correct code for this rule with the "always", { "avoidQuotes": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidQuotes": true }]*/
/*eslint-env es6*/
var foo = {
"bar-baz": function() {},
"qux": qux
};
ignoreConstructors
{
"object-shorthand": ["error", "always", { "ignoreConstructors": true }]
}
Example of correct code for this rule with the "always", { "ignoreConstructors": true }
option:
/*eslint object-shorthand: ["error", "always", { "ignoreConstructors": true }]*/
/*eslint-env es6*/
var foo = {
ConstructorFunction: function() {}
};
avoidExplicitReturnArrows
{
"object-shorthand": ["error", "always", { "avoidExplicitReturnArrows": true }]
}
Example of incorrect code for this rule with the "always", { "avoidExplicitReturnArrows": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidExplicitReturnArrows": true }]*/
/*eslint-env es6*/
var foo = {
foo: (bar, baz) => {
return bar + baz;
},
qux: (foobar) => {
return foobar * 2;
}
};
Example of correct code for this rule with the "always", { "avoidExplicitReturnArrows": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidExplicitReturnArrows": true }]*/
/*eslint-env es6*/
var foo = {
foo(bar, baz) {
return bar + baz;
},
qux: foobar => foobar * 2
};
Example of incorrect code for this rule with the "consistent"
option:
/*eslint object-shorthand: [2, "consistent"]*/
/*eslint-env es6*/
var foo = {
a,
b: "foo",
};
Examples of correct code for this rule with the "consistent"
option:
/*eslint object-shorthand: [2, "consistent"]*/
/*eslint-env es6*/
var foo = {
a: a,
b: "foo"
};
var bar = {
a,
b,
};
Example of incorrect code with the "consistent-as-needed"
option, which is very similar to "consistent"
:
/*eslint object-shorthand: [2, "consistent-as-needed"]*/
/*eslint-env es6*/
var foo = {
a: a,
b: b,
};
When Not To Use It
Anyone not yet in an ES6 environment would not want to apply this rule. Others may find the terseness of the shorthand syntax harder to read and may not want to encourage it with this rule.
Further Reading
Object initializer - MDN Source: http://eslint.org/docs/rules/
Expected property shorthand. Open
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Require Object Literal Shorthand Syntax (object-shorthand)
ECMAScript 6 provides a concise form for defining object literal methods and properties. This syntax can make defining complex object literals much cleaner.
Here are a few common examples using the ES5 syntax:
// properties
var foo = {
x: x,
y: y,
z: z,
};
// methods
var foo = {
a: function() {},
b: function() {}
};
Now here are ES6 equivalents:
/*eslint-env es6*/
// properties
var foo = {x, y, z};
// methods
var foo = {
a() {},
b() {}
};
Rule Details
This rule enforces the use of the shorthand syntax. This applies to all methods (including generators) defined in object literals and any properties defined where the key name matches name of the assigned variable.
Each of the following properties would warn:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
w: function() {},
x: function *() {},
[y]: function() {},
z: z
};
In that case the expected syntax would have been:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
w() {},
*x() {},
[y]() {},
z
};
This rule does not flag arrow functions inside of object literals. The following will not warn:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
x: (y) => y
};
See Also:
-
no-useless-rename
which disallows renaming import, export, and destructured assignments to the same name.
Options
The rule takes an option which specifies when it should be applied. It can be set to one of the following values:
-
"always"
(default) expects that the shorthand will be used whenever possible. -
"methods"
ensures the method shorthand is used (also applies to generators). -
"properties"
ensures the property shorthand is used (where the key and variable name match). -
"never"
ensures that no property or method shorthand is used in any object literal. -
"consistent"
ensures that either all shorthand or all long-form will be used in an object literal. -
"consistent-as-needed"
ensures that either all shorthand or all long-form will be used in an object literal, but ensures all shorthand whenever possible.
You can set the option in configuration like this:
{
"object-shorthand": ["error", "always"]
}
Additionally, the rule takes an optional object configuration:
-
"avoidQuotes": true
indicates that long-form syntax is preferred whenever the object key is a string literal (default:false
). Note that this option can only be enabled when the string option is set to"always"
,"methods"
, or"properties"
. -
"ignoreConstructors": true
can be used to prevent the rule from reporting errors for constructor functions. (By default, the rule treats constructors the same way as other functions.) Note that this option can only be enabled when the string option is set to"always"
or"methods"
. -
"avoidExplicitReturnArrows": true
indicates that methods are preferred over explicit-return arrow functions for function properties. (By default, the rule allows either of these.) Note that this option can only be enabled when the string option is set to"always"
or"methods"
.
avoidQuotes
{
"object-shorthand": ["error", "always", { "avoidQuotes": true }]
}
Example of incorrect code for this rule with the "always", { "avoidQuotes": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidQuotes": true }]*/
/*eslint-env es6*/
var foo = {
"bar-baz"() {}
};
Example of correct code for this rule with the "always", { "avoidQuotes": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidQuotes": true }]*/
/*eslint-env es6*/
var foo = {
"bar-baz": function() {},
"qux": qux
};
ignoreConstructors
{
"object-shorthand": ["error", "always", { "ignoreConstructors": true }]
}
Example of correct code for this rule with the "always", { "ignoreConstructors": true }
option:
/*eslint object-shorthand: ["error", "always", { "ignoreConstructors": true }]*/
/*eslint-env es6*/
var foo = {
ConstructorFunction: function() {}
};
avoidExplicitReturnArrows
{
"object-shorthand": ["error", "always", { "avoidExplicitReturnArrows": true }]
}
Example of incorrect code for this rule with the "always", { "avoidExplicitReturnArrows": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidExplicitReturnArrows": true }]*/
/*eslint-env es6*/
var foo = {
foo: (bar, baz) => {
return bar + baz;
},
qux: (foobar) => {
return foobar * 2;
}
};
Example of correct code for this rule with the "always", { "avoidExplicitReturnArrows": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidExplicitReturnArrows": true }]*/
/*eslint-env es6*/
var foo = {
foo(bar, baz) {
return bar + baz;
},
qux: foobar => foobar * 2
};
Example of incorrect code for this rule with the "consistent"
option:
/*eslint object-shorthand: [2, "consistent"]*/
/*eslint-env es6*/
var foo = {
a,
b: "foo",
};
Examples of correct code for this rule with the "consistent"
option:
/*eslint object-shorthand: [2, "consistent"]*/
/*eslint-env es6*/
var foo = {
a: a,
b: "foo"
};
var bar = {
a,
b,
};
Example of incorrect code with the "consistent-as-needed"
option, which is very similar to "consistent"
:
/*eslint object-shorthand: [2, "consistent-as-needed"]*/
/*eslint-env es6*/
var foo = {
a: a,
b: b,
};
When Not To Use It
Anyone not yet in an ES6 environment would not want to apply this rule. Others may find the terseness of the shorthand syntax harder to read and may not want to encourage it with this rule.
Further Reading
Object initializer - MDN Source: http://eslint.org/docs/rules/
A space is required before '}'. Open
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Identifier 'expand_mode' is not in camel case. Open
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Require CamelCase (camelcase)
When it comes to naming variables, style guides generally fall into one of two camps: camelcase (variableName
) and underscores (variable_name
). This rule focuses on using the camelcase approach. If your style guide calls for camelCasing your variable names, then this rule is for you!
Rule Details
This rule looks for any underscores (_
) located within the source code. It ignores leading and trailing underscores and only checks those in the middle of a variable name. If ESLint decides that the variable is a constant (all uppercase), then no warning will be thrown. Otherwise, a warning will be thrown. This rule only flags definitions and assignments but not function calls. In case of ES6 import
statements, this rule only targets the name of the variable that will be imported into the local module scope.
Options
This rule has an object option:
-
"properties": "always"
(default) enforces camelcase style for property names -
"properties": "never"
does not check property names -
"ignoreDestructuring": false
(default) enforces camelcase style for destructured identifiers -
"ignoreDestructuring": true
does not check destructured identifiers -
allow
(string[]
) list of properties to accept. Accept regex.
properties: "always"
Examples of incorrect code for this rule with the default { "properties": "always" }
option:
/*eslint camelcase: "error"*/
import { no_camelcased } from "external-module"
var my_favorite_color = "#112C85";
function do_something() {
// ...
}
obj.do_something = function() {
// ...
};
function foo({ no_camelcased }) {
// ...
};
function foo({ isCamelcased: no_camelcased }) {
// ...
}
function foo({ no_camelcased = 'default value' }) {
// ...
};
var obj = {
my_pref: 1
};
var { category_id = 1 } = query;
var { foo: no_camelcased } = bar;
var { foo: bar_baz = 1 } = quz;
Examples of correct code for this rule with the default { "properties": "always" }
option:
/*eslint camelcase: "error"*/
import { no_camelcased as camelCased } from "external-module";
var myFavoriteColor = "#112C85";
var _myFavoriteColor = "#112C85";
var myFavoriteColor_ = "#112C85";
var MY_FAVORITE_COLOR = "#112C85";
var foo = bar.baz_boom;
var foo = { qux: bar.baz_boom };
obj.do_something();
do_something();
new do_something();
var { category_id: category } = query;
function foo({ isCamelCased }) {
// ...
};
function foo({ isCamelCased: isAlsoCamelCased }) {
// ...
}
function foo({ isCamelCased = 'default value' }) {
// ...
};
var { categoryId = 1 } = query;
var { foo: isCamelCased } = bar;
var { foo: isCamelCased = 1 } = quz;
properties: "never"
Examples of correct code for this rule with the { "properties": "never" }
option:
/*eslint camelcase: ["error", {properties: "never"}]*/
var obj = {
my_pref: 1
};
ignoreDestructuring: false
Examples of incorrect code for this rule with the default { "ignoreDestructuring": false }
option:
/*eslint camelcase: "error"*/
var { category_id } = query;
var { category_id = 1 } = query;
var { category_id: category_id } = query;
var { category_id: category_alias } = query;
var { category_id: categoryId, ...other_props } = query;
ignoreDestructuring: true
Examples of incorrect code for this rule with the { "ignoreDestructuring": true }
option:
/*eslint camelcase: ["error", {ignoreDestructuring: true}]*/
var { category_id: category_alias } = query;
var { category_id, ...other_props } = query;
Examples of correct code for this rule with the { "ignoreDestructuring": true }
option:
/*eslint camelcase: ["error", {ignoreDestructuring: true}]*/
var { category_id } = query;
var { category_id = 1 } = query;
var { category_id: category_id } = query;
allow
Examples of correct code for this rule with the allow
option:
/*eslint camelcase: ["error", {allow: ["UNSAFE_componentWillMount"]}]*/
function UNSAFE_componentWillMount() {
// ...
}
/*eslint camelcase: ["error", {allow: ["^UNSAFE_"]}]*/
function UNSAFE_componentWillMount() {
// ...
}
function UNSAFE_componentWillMount() {
// ...
}
When Not To Use It
If you have established coding standards using a different naming convention (separating words with underscores), turn this rule off. Source: http://eslint.org/docs/rules/
All 'var' declarations must be at the top of the function scope. Open
var selectedKeys = [];
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Require Variable Declarations to be at the top of their scope (vars-on-top)
The vars-on-top
rule generates warnings when variable declarations are not used serially at the top of a function scope or the top of a program.
By default variable declarations are always moved (“hoisted”) invisibly to the top of their containing scope by the JavaScript interpreter.
This rule forces the programmer to represent that behavior by manually moving the variable declaration to the top of its containing scope.
Rule Details
This rule aims to keep all variable declarations in the leading series of statements. Allowing multiple declarations helps promote maintainability and is thus allowed.
Examples of incorrect code for this rule:
/*eslint vars-on-top: "error"*/
// Variable declarations in a block:
function doSomething() {
var first;
if (true) {
first = true;
}
var second;
}
// Variable declaration in for initializer:
function doSomething() {
for (var i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
// Variables after other statements:
f();
var a;
Examples of correct code for this rule:
/*eslint vars-on-top: "error"*/
function doSomething() {
var first;
var second; //multiple declarations are allowed at the top
if (true) {
first = true;
}
}
function doSomething() {
var i;
for (i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
var a;
f();
/*eslint vars-on-top: "error"*/
// Directives may precede variable declarations.
"use strict";
var a;
f();
// Comments can describe variables.
function doSomething() {
// this is the first var.
var first;
// this is the second var.
var second
}
Further Reading
A space is required after '{'. Open
miqJqueryRequest(ManageIQ.tree.clickUrl + encodeURIComponent(id), {beforeSend: true, complete: true});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
var url = ManageIQ.tree.clickUrl + '?node_id=' + encodeURIComponent(id) + '&node_clicked=1';
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Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
Missing semicolon. Open
}
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
for (var i = 0; i < sessionStorage.length; i++) {
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Identifier 'selected_node' is not in camel case. Open
window.miqAddNodeChildren = function(treename, key, selected_node, children) {
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Require CamelCase (camelcase)
When it comes to naming variables, style guides generally fall into one of two camps: camelcase (variableName
) and underscores (variable_name
). This rule focuses on using the camelcase approach. If your style guide calls for camelCasing your variable names, then this rule is for you!
Rule Details
This rule looks for any underscores (_
) located within the source code. It ignores leading and trailing underscores and only checks those in the middle of a variable name. If ESLint decides that the variable is a constant (all uppercase), then no warning will be thrown. Otherwise, a warning will be thrown. This rule only flags definitions and assignments but not function calls. In case of ES6 import
statements, this rule only targets the name of the variable that will be imported into the local module scope.
Options
This rule has an object option:
-
"properties": "always"
(default) enforces camelcase style for property names -
"properties": "never"
does not check property names -
"ignoreDestructuring": false
(default) enforces camelcase style for destructured identifiers -
"ignoreDestructuring": true
does not check destructured identifiers -
allow
(string[]
) list of properties to accept. Accept regex.
properties: "always"
Examples of incorrect code for this rule with the default { "properties": "always" }
option:
/*eslint camelcase: "error"*/
import { no_camelcased } from "external-module"
var my_favorite_color = "#112C85";
function do_something() {
// ...
}
obj.do_something = function() {
// ...
};
function foo({ no_camelcased }) {
// ...
};
function foo({ isCamelcased: no_camelcased }) {
// ...
}
function foo({ no_camelcased = 'default value' }) {
// ...
};
var obj = {
my_pref: 1
};
var { category_id = 1 } = query;
var { foo: no_camelcased } = bar;
var { foo: bar_baz = 1 } = quz;
Examples of correct code for this rule with the default { "properties": "always" }
option:
/*eslint camelcase: "error"*/
import { no_camelcased as camelCased } from "external-module";
var myFavoriteColor = "#112C85";
var _myFavoriteColor = "#112C85";
var myFavoriteColor_ = "#112C85";
var MY_FAVORITE_COLOR = "#112C85";
var foo = bar.baz_boom;
var foo = { qux: bar.baz_boom };
obj.do_something();
do_something();
new do_something();
var { category_id: category } = query;
function foo({ isCamelCased }) {
// ...
};
function foo({ isCamelCased: isAlsoCamelCased }) {
// ...
}
function foo({ isCamelCased = 'default value' }) {
// ...
};
var { categoryId = 1 } = query;
var { foo: isCamelCased } = bar;
var { foo: isCamelCased = 1 } = quz;
properties: "never"
Examples of correct code for this rule with the { "properties": "never" }
option:
/*eslint camelcase: ["error", {properties: "never"}]*/
var obj = {
my_pref: 1
};
ignoreDestructuring: false
Examples of incorrect code for this rule with the default { "ignoreDestructuring": false }
option:
/*eslint camelcase: "error"*/
var { category_id } = query;
var { category_id = 1 } = query;
var { category_id: category_id } = query;
var { category_id: category_alias } = query;
var { category_id: categoryId, ...other_props } = query;
ignoreDestructuring: true
Examples of incorrect code for this rule with the { "ignoreDestructuring": true }
option:
/*eslint camelcase: ["error", {ignoreDestructuring: true}]*/
var { category_id: category_alias } = query;
var { category_id, ...other_props } = query;
Examples of correct code for this rule with the { "ignoreDestructuring": true }
option:
/*eslint camelcase: ["error", {ignoreDestructuring: true}]*/
var { category_id } = query;
var { category_id = 1 } = query;
var { category_id: category_id } = query;
allow
Examples of correct code for this rule with the allow
option:
/*eslint camelcase: ["error", {allow: ["UNSAFE_componentWillMount"]}]*/
function UNSAFE_componentWillMount() {
// ...
}
/*eslint camelcase: ["error", {allow: ["^UNSAFE_"]}]*/
function UNSAFE_componentWillMount() {
// ...
}
function UNSAFE_componentWillMount() {
// ...
}
When Not To Use It
If you have established coding standards using a different naming convention (separating words with underscores), turn this rule off. Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var node = miqTreeFindNodeByKey(treename, key);
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
A space is required before '}'. Open
ManageIQ.redux.store.dispatch({namespace: tree, type: '@@tree/expandNode', key: key});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
A space is required after '{'. Open
ManageIQ.redux.store.dispatch({namespace: tree, type: '@@tree/scrollToNode', key: key});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var offset = 0; // Calculate the required scrolling offset
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
obj = $('miq-tree-view[name="' + tree + '"] > .treeview').treeview(true);
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Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
Identifier 'tree_prefix' is not in camel case. Open
window.miqDeleteTreeCookies = function(tree_prefix) {
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Require CamelCase (camelcase)
When it comes to naming variables, style guides generally fall into one of two camps: camelcase (variableName
) and underscores (variable_name
). This rule focuses on using the camelcase approach. If your style guide calls for camelCasing your variable names, then this rule is for you!
Rule Details
This rule looks for any underscores (_
) located within the source code. It ignores leading and trailing underscores and only checks those in the middle of a variable name. If ESLint decides that the variable is a constant (all uppercase), then no warning will be thrown. Otherwise, a warning will be thrown. This rule only flags definitions and assignments but not function calls. In case of ES6 import
statements, this rule only targets the name of the variable that will be imported into the local module scope.
Options
This rule has an object option:
-
"properties": "always"
(default) enforces camelcase style for property names -
"properties": "never"
does not check property names -
"ignoreDestructuring": false
(default) enforces camelcase style for destructured identifiers -
"ignoreDestructuring": true
does not check destructured identifiers -
allow
(string[]
) list of properties to accept. Accept regex.
properties: "always"
Examples of incorrect code for this rule with the default { "properties": "always" }
option:
/*eslint camelcase: "error"*/
import { no_camelcased } from "external-module"
var my_favorite_color = "#112C85";
function do_something() {
// ...
}
obj.do_something = function() {
// ...
};
function foo({ no_camelcased }) {
// ...
};
function foo({ isCamelcased: no_camelcased }) {
// ...
}
function foo({ no_camelcased = 'default value' }) {
// ...
};
var obj = {
my_pref: 1
};
var { category_id = 1 } = query;
var { foo: no_camelcased } = bar;
var { foo: bar_baz = 1 } = quz;
Examples of correct code for this rule with the default { "properties": "always" }
option:
/*eslint camelcase: "error"*/
import { no_camelcased as camelCased } from "external-module";
var myFavoriteColor = "#112C85";
var _myFavoriteColor = "#112C85";
var myFavoriteColor_ = "#112C85";
var MY_FAVORITE_COLOR = "#112C85";
var foo = bar.baz_boom;
var foo = { qux: bar.baz_boom };
obj.do_something();
do_something();
new do_something();
var { category_id: category } = query;
function foo({ isCamelCased }) {
// ...
};
function foo({ isCamelCased: isAlsoCamelCased }) {
// ...
}
function foo({ isCamelCased = 'default value' }) {
// ...
};
var { categoryId = 1 } = query;
var { foo: isCamelCased } = bar;
var { foo: isCamelCased = 1 } = quz;
properties: "never"
Examples of correct code for this rule with the { "properties": "never" }
option:
/*eslint camelcase: ["error", {properties: "never"}]*/
var obj = {
my_pref: 1
};
ignoreDestructuring: false
Examples of incorrect code for this rule with the default { "ignoreDestructuring": false }
option:
/*eslint camelcase: "error"*/
var { category_id } = query;
var { category_id = 1 } = query;
var { category_id: category_id } = query;
var { category_id: category_alias } = query;
var { category_id: categoryId, ...other_props } = query;
ignoreDestructuring: true
Examples of incorrect code for this rule with the { "ignoreDestructuring": true }
option:
/*eslint camelcase: ["error", {ignoreDestructuring: true}]*/
var { category_id: category_alias } = query;
var { category_id, ...other_props } = query;
Examples of correct code for this rule with the { "ignoreDestructuring": true }
option:
/*eslint camelcase: ["error", {ignoreDestructuring: true}]*/
var { category_id } = query;
var { category_id = 1 } = query;
var { category_id: category_id } = query;
allow
Examples of correct code for this rule with the allow
option:
/*eslint camelcase: ["error", {allow: ["UNSAFE_componentWillMount"]}]*/
function UNSAFE_componentWillMount() {
// ...
}
/*eslint camelcase: ["error", {allow: ["^UNSAFE_"]}]*/
function UNSAFE_componentWillMount() {
// ...
}
function UNSAFE_componentWillMount() {
// ...
}
When Not To Use It
If you have established coding standards using a different naming convention (separating words with underscores), turn this rule off. Source: http://eslint.org/docs/rules/
Missing semicolon. Open
}
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
A space is required before '}'. Open
miqJqueryRequest(url, {data: {all_checked: selectedKeys}});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Missing semicolon. Open
}
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var node = miqTreeFindNodeByKey(treename, key);
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- Exclude checks
require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected function expression. Open
node.nodes.slice().forEach(function(child) {
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Require using arrow functions for callbacks (prefer-arrow-callback)
Arrow functions can be an attractive alternative to function expressions for callbacks or function arguments.
For example, arrow functions are automatically bound to their surrounding scope/context. This provides an alternative to the pre-ES6 standard of explicitly binding function expressions to achieve similar behavior.
Additionally, arrow functions are:
less verbose, and easier to reason about.
bound lexically regardless of where or when they are invoked.
Rule Details
This rule locates function expressions used as callbacks or function arguments. An error will be produced for any that could be replaced by an arrow function without changing the result.
The following examples will be flagged:
/* eslint prefer-arrow-callback: "error" */
foo(function(a) { return a; }); // ERROR
// prefer: foo(a => a)
foo(function() { return this.a; }.bind(this)); // ERROR
// prefer: foo(() => this.a)
Instances where an arrow function would not produce identical results will be ignored.
The following examples will not be flagged:
/* eslint prefer-arrow-callback: "error" */
/* eslint-env es6 */
// arrow function callback
foo(a => a); // OK
// generator as callback
foo(function*() { yield; }); // OK
// function expression not used as callback or function argument
var foo = function foo(a) { return a; }; // OK
// unbound function expression callback
foo(function() { return this.a; }); // OK
// recursive named function callback
foo(function bar(n) { return n && n + bar(n - 1); }); // OK
Options
Access further control over this rule's behavior via an options object.
Default: { allowNamedFunctions: false, allowUnboundThis: true }
allowNamedFunctions
By default { "allowNamedFunctions": false }
, this boolean
option prohibits using named functions as callbacks or function arguments.
Changing this value to true
will reverse this option's behavior by allowing use of named functions without restriction.
{ "allowNamedFunctions": true }
will not flag the following example:
/* eslint prefer-arrow-callback: [ "error", { "allowNamedFunctions": true } ] */
foo(function bar() {});
allowUnboundThis
By default { "allowUnboundThis": true }
, this boolean
option allows function expressions containing this
to be used as callbacks, as long as the function in question has not been explicitly bound.
When set to false
this option prohibits the use of function expressions as callbacks or function arguments entirely, without exception.
{ "allowUnboundThis": false }
will flag the following examples:
/* eslint prefer-arrow-callback: [ "error", { "allowUnboundThis": false } ] */
/* eslint-env es6 */
foo(function() { this.a; });
foo(function() { (() => this); });
someArray.map(function(itm) { return this.doSomething(itm); }, someObject);
When Not To Use It
In environments that have not yet adopted ES6 language features (ES3/5).
In ES6+ environments that allow the use of function expressions when describing callbacks or function arguments.
Further Reading
Missing semicolon. Open
}
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- Exclude checks
require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var nid = ids[ids.length - 1].split('-'); // Get the last part of the node id
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- Exclude checks
require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
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Require Object Literal Shorthand Syntax (object-shorthand)
ECMAScript 6 provides a concise form for defining object literal methods and properties. This syntax can make defining complex object literals much cleaner.
Here are a few common examples using the ES5 syntax:
// properties
var foo = {
x: x,
y: y,
z: z,
};
// methods
var foo = {
a: function() {},
b: function() {}
};
Now here are ES6 equivalents:
/*eslint-env es6*/
// properties
var foo = {x, y, z};
// methods
var foo = {
a() {},
b() {}
};
Rule Details
This rule enforces the use of the shorthand syntax. This applies to all methods (including generators) defined in object literals and any properties defined where the key name matches name of the assigned variable.
Each of the following properties would warn:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
w: function() {},
x: function *() {},
[y]: function() {},
z: z
};
In that case the expected syntax would have been:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
w() {},
*x() {},
[y]() {},
z
};
This rule does not flag arrow functions inside of object literals. The following will not warn:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
x: (y) => y
};
See Also:
-
no-useless-rename
which disallows renaming import, export, and destructured assignments to the same name.
Options
The rule takes an option which specifies when it should be applied. It can be set to one of the following values:
-
"always"
(default) expects that the shorthand will be used whenever possible. -
"methods"
ensures the method shorthand is used (also applies to generators). -
"properties"
ensures the property shorthand is used (where the key and variable name match). -
"never"
ensures that no property or method shorthand is used in any object literal. -
"consistent"
ensures that either all shorthand or all long-form will be used in an object literal. -
"consistent-as-needed"
ensures that either all shorthand or all long-form will be used in an object literal, but ensures all shorthand whenever possible.
You can set the option in configuration like this:
{
"object-shorthand": ["error", "always"]
}
Additionally, the rule takes an optional object configuration:
-
"avoidQuotes": true
indicates that long-form syntax is preferred whenever the object key is a string literal (default:false
). Note that this option can only be enabled when the string option is set to"always"
,"methods"
, or"properties"
. -
"ignoreConstructors": true
can be used to prevent the rule from reporting errors for constructor functions. (By default, the rule treats constructors the same way as other functions.) Note that this option can only be enabled when the string option is set to"always"
or"methods"
. -
"avoidExplicitReturnArrows": true
indicates that methods are preferred over explicit-return arrow functions for function properties. (By default, the rule allows either of these.) Note that this option can only be enabled when the string option is set to"always"
or"methods"
.
avoidQuotes
{
"object-shorthand": ["error", "always", { "avoidQuotes": true }]
}
Example of incorrect code for this rule with the "always", { "avoidQuotes": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidQuotes": true }]*/
/*eslint-env es6*/
var foo = {
"bar-baz"() {}
};
Example of correct code for this rule with the "always", { "avoidQuotes": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidQuotes": true }]*/
/*eslint-env es6*/
var foo = {
"bar-baz": function() {},
"qux": qux
};
ignoreConstructors
{
"object-shorthand": ["error", "always", { "ignoreConstructors": true }]
}
Example of correct code for this rule with the "always", { "ignoreConstructors": true }
option:
/*eslint object-shorthand: ["error", "always", { "ignoreConstructors": true }]*/
/*eslint-env es6*/
var foo = {
ConstructorFunction: function() {}
};
avoidExplicitReturnArrows
{
"object-shorthand": ["error", "always", { "avoidExplicitReturnArrows": true }]
}
Example of incorrect code for this rule with the "always", { "avoidExplicitReturnArrows": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidExplicitReturnArrows": true }]*/
/*eslint-env es6*/
var foo = {
foo: (bar, baz) => {
return bar + baz;
},
qux: (foobar) => {
return foobar * 2;
}
};
Example of correct code for this rule with the "always", { "avoidExplicitReturnArrows": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidExplicitReturnArrows": true }]*/
/*eslint-env es6*/
var foo = {
foo(bar, baz) {
return bar + baz;
},
qux: foobar => foobar * 2
};
Example of incorrect code for this rule with the "consistent"
option:
/*eslint object-shorthand: [2, "consistent"]*/
/*eslint-env es6*/
var foo = {
a,
b: "foo",
};
Examples of correct code for this rule with the "consistent"
option:
/*eslint object-shorthand: [2, "consistent"]*/
/*eslint-env es6*/
var foo = {
a: a,
b: "foo"
};
var bar = {
a,
b,
};
Example of incorrect code with the "consistent-as-needed"
option, which is very similar to "consistent"
:
/*eslint object-shorthand: [2, "consistent-as-needed"]*/
/*eslint-env es6*/
var foo = {
a: a,
b: b,
};
When Not To Use It
Anyone not yet in an ES6 environment would not want to apply this rule. Others may find the terseness of the shorthand syntax harder to read and may not want to encourage it with this rule.
Further Reading
Object initializer - MDN Source: http://eslint.org/docs/rules/
Missing semicolon. Open
}
- Read upRead up
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- Exclude checks
require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Missing semicolon. Open
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
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Require using arrow functions for callbacks (prefer-arrow-callback)
Arrow functions can be an attractive alternative to function expressions for callbacks or function arguments.
For example, arrow functions are automatically bound to their surrounding scope/context. This provides an alternative to the pre-ES6 standard of explicitly binding function expressions to achieve similar behavior.
Additionally, arrow functions are:
less verbose, and easier to reason about.
bound lexically regardless of where or when they are invoked.
Rule Details
This rule locates function expressions used as callbacks or function arguments. An error will be produced for any that could be replaced by an arrow function without changing the result.
The following examples will be flagged:
/* eslint prefer-arrow-callback: "error" */
foo(function(a) { return a; }); // ERROR
// prefer: foo(a => a)
foo(function() { return this.a; }.bind(this)); // ERROR
// prefer: foo(() => this.a)
Instances where an arrow function would not produce identical results will be ignored.
The following examples will not be flagged:
/* eslint prefer-arrow-callback: "error" */
/* eslint-env es6 */
// arrow function callback
foo(a => a); // OK
// generator as callback
foo(function*() { yield; }); // OK
// function expression not used as callback or function argument
var foo = function foo(a) { return a; }; // OK
// unbound function expression callback
foo(function() { return this.a; }); // OK
// recursive named function callback
foo(function bar(n) { return n && n + bar(n - 1); }); // OK
Options
Access further control over this rule's behavior via an options object.
Default: { allowNamedFunctions: false, allowUnboundThis: true }
allowNamedFunctions
By default { "allowNamedFunctions": false }
, this boolean
option prohibits using named functions as callbacks or function arguments.
Changing this value to true
will reverse this option's behavior by allowing use of named functions without restriction.
{ "allowNamedFunctions": true }
will not flag the following example:
/* eslint prefer-arrow-callback: [ "error", { "allowNamedFunctions": true } ] */
foo(function bar() {});
allowUnboundThis
By default { "allowUnboundThis": true }
, this boolean
option allows function expressions containing this
to be used as callbacks, as long as the function in question has not been explicitly bound.
When set to false
this option prohibits the use of function expressions as callbacks or function arguments entirely, without exception.
{ "allowUnboundThis": false }
will flag the following examples:
/* eslint prefer-arrow-callback: [ "error", { "allowUnboundThis": false } ] */
/* eslint-env es6 */
foo(function() { this.a; });
foo(function() { (() => this); });
someArray.map(function(itm) { return this.doSomething(itm); }, someObject);
When Not To Use It
In environments that have not yet adopted ES6 language features (ES3/5).
In ES6+ environments that allow the use of function expressions when describing callbacks or function arguments.
Further Reading
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Require Object Literal Shorthand Syntax (object-shorthand)
ECMAScript 6 provides a concise form for defining object literal methods and properties. This syntax can make defining complex object literals much cleaner.
Here are a few common examples using the ES5 syntax:
// properties
var foo = {
x: x,
y: y,
z: z,
};
// methods
var foo = {
a: function() {},
b: function() {}
};
Now here are ES6 equivalents:
/*eslint-env es6*/
// properties
var foo = {x, y, z};
// methods
var foo = {
a() {},
b() {}
};
Rule Details
This rule enforces the use of the shorthand syntax. This applies to all methods (including generators) defined in object literals and any properties defined where the key name matches name of the assigned variable.
Each of the following properties would warn:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
w: function() {},
x: function *() {},
[y]: function() {},
z: z
};
In that case the expected syntax would have been:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
w() {},
*x() {},
[y]() {},
z
};
This rule does not flag arrow functions inside of object literals. The following will not warn:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
x: (y) => y
};
See Also:
-
no-useless-rename
which disallows renaming import, export, and destructured assignments to the same name.
Options
The rule takes an option which specifies when it should be applied. It can be set to one of the following values:
-
"always"
(default) expects that the shorthand will be used whenever possible. -
"methods"
ensures the method shorthand is used (also applies to generators). -
"properties"
ensures the property shorthand is used (where the key and variable name match). -
"never"
ensures that no property or method shorthand is used in any object literal. -
"consistent"
ensures that either all shorthand or all long-form will be used in an object literal. -
"consistent-as-needed"
ensures that either all shorthand or all long-form will be used in an object literal, but ensures all shorthand whenever possible.
You can set the option in configuration like this:
{
"object-shorthand": ["error", "always"]
}
Additionally, the rule takes an optional object configuration:
-
"avoidQuotes": true
indicates that long-form syntax is preferred whenever the object key is a string literal (default:false
). Note that this option can only be enabled when the string option is set to"always"
,"methods"
, or"properties"
. -
"ignoreConstructors": true
can be used to prevent the rule from reporting errors for constructor functions. (By default, the rule treats constructors the same way as other functions.) Note that this option can only be enabled when the string option is set to"always"
or"methods"
. -
"avoidExplicitReturnArrows": true
indicates that methods are preferred over explicit-return arrow functions for function properties. (By default, the rule allows either of these.) Note that this option can only be enabled when the string option is set to"always"
or"methods"
.
avoidQuotes
{
"object-shorthand": ["error", "always", { "avoidQuotes": true }]
}
Example of incorrect code for this rule with the "always", { "avoidQuotes": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidQuotes": true }]*/
/*eslint-env es6*/
var foo = {
"bar-baz"() {}
};
Example of correct code for this rule with the "always", { "avoidQuotes": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidQuotes": true }]*/
/*eslint-env es6*/
var foo = {
"bar-baz": function() {},
"qux": qux
};
ignoreConstructors
{
"object-shorthand": ["error", "always", { "ignoreConstructors": true }]
}
Example of correct code for this rule with the "always", { "ignoreConstructors": true }
option:
/*eslint object-shorthand: ["error", "always", { "ignoreConstructors": true }]*/
/*eslint-env es6*/
var foo = {
ConstructorFunction: function() {}
};
avoidExplicitReturnArrows
{
"object-shorthand": ["error", "always", { "avoidExplicitReturnArrows": true }]
}
Example of incorrect code for this rule with the "always", { "avoidExplicitReturnArrows": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidExplicitReturnArrows": true }]*/
/*eslint-env es6*/
var foo = {
foo: (bar, baz) => {
return bar + baz;
},
qux: (foobar) => {
return foobar * 2;
}
};
Example of correct code for this rule with the "always", { "avoidExplicitReturnArrows": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidExplicitReturnArrows": true }]*/
/*eslint-env es6*/
var foo = {
foo(bar, baz) {
return bar + baz;
},
qux: foobar => foobar * 2
};
Example of incorrect code for this rule with the "consistent"
option:
/*eslint object-shorthand: [2, "consistent"]*/
/*eslint-env es6*/
var foo = {
a,
b: "foo",
};
Examples of correct code for this rule with the "consistent"
option:
/*eslint object-shorthand: [2, "consistent"]*/
/*eslint-env es6*/
var foo = {
a: a,
b: "foo"
};
var bar = {
a,
b,
};
Example of incorrect code with the "consistent-as-needed"
option, which is very similar to "consistent"
:
/*eslint object-shorthand: [2, "consistent-as-needed"]*/
/*eslint-env es6*/
var foo = {
a: a,
b: b,
};
When Not To Use It
Anyone not yet in an ES6 environment would not want to apply this rule. Others may find the terseness of the shorthand syntax harder to read and may not want to encourage it with this rule.
Further Reading
Object initializer - MDN Source: http://eslint.org/docs/rules/
Identifier 'selected_id' is not in camel case. Open
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Require CamelCase (camelcase)
When it comes to naming variables, style guides generally fall into one of two camps: camelcase (variableName
) and underscores (variable_name
). This rule focuses on using the camelcase approach. If your style guide calls for camelCasing your variable names, then this rule is for you!
Rule Details
This rule looks for any underscores (_
) located within the source code. It ignores leading and trailing underscores and only checks those in the middle of a variable name. If ESLint decides that the variable is a constant (all uppercase), then no warning will be thrown. Otherwise, a warning will be thrown. This rule only flags definitions and assignments but not function calls. In case of ES6 import
statements, this rule only targets the name of the variable that will be imported into the local module scope.
Options
This rule has an object option:
-
"properties": "always"
(default) enforces camelcase style for property names -
"properties": "never"
does not check property names -
"ignoreDestructuring": false
(default) enforces camelcase style for destructured identifiers -
"ignoreDestructuring": true
does not check destructured identifiers -
allow
(string[]
) list of properties to accept. Accept regex.
properties: "always"
Examples of incorrect code for this rule with the default { "properties": "always" }
option:
/*eslint camelcase: "error"*/
import { no_camelcased } from "external-module"
var my_favorite_color = "#112C85";
function do_something() {
// ...
}
obj.do_something = function() {
// ...
};
function foo({ no_camelcased }) {
// ...
};
function foo({ isCamelcased: no_camelcased }) {
// ...
}
function foo({ no_camelcased = 'default value' }) {
// ...
};
var obj = {
my_pref: 1
};
var { category_id = 1 } = query;
var { foo: no_camelcased } = bar;
var { foo: bar_baz = 1 } = quz;
Examples of correct code for this rule with the default { "properties": "always" }
option:
/*eslint camelcase: "error"*/
import { no_camelcased as camelCased } from "external-module";
var myFavoriteColor = "#112C85";
var _myFavoriteColor = "#112C85";
var myFavoriteColor_ = "#112C85";
var MY_FAVORITE_COLOR = "#112C85";
var foo = bar.baz_boom;
var foo = { qux: bar.baz_boom };
obj.do_something();
do_something();
new do_something();
var { category_id: category } = query;
function foo({ isCamelCased }) {
// ...
};
function foo({ isCamelCased: isAlsoCamelCased }) {
// ...
}
function foo({ isCamelCased = 'default value' }) {
// ...
};
var { categoryId = 1 } = query;
var { foo: isCamelCased } = bar;
var { foo: isCamelCased = 1 } = quz;
properties: "never"
Examples of correct code for this rule with the { "properties": "never" }
option:
/*eslint camelcase: ["error", {properties: "never"}]*/
var obj = {
my_pref: 1
};
ignoreDestructuring: false
Examples of incorrect code for this rule with the default { "ignoreDestructuring": false }
option:
/*eslint camelcase: "error"*/
var { category_id } = query;
var { category_id = 1 } = query;
var { category_id: category_id } = query;
var { category_id: category_alias } = query;
var { category_id: categoryId, ...other_props } = query;
ignoreDestructuring: true
Examples of incorrect code for this rule with the { "ignoreDestructuring": true }
option:
/*eslint camelcase: ["error", {ignoreDestructuring: true}]*/
var { category_id: category_alias } = query;
var { category_id, ...other_props } = query;
Examples of correct code for this rule with the { "ignoreDestructuring": true }
option:
/*eslint camelcase: ["error", {ignoreDestructuring: true}]*/
var { category_id } = query;
var { category_id = 1 } = query;
var { category_id: category_id } = query;
allow
Examples of correct code for this rule with the allow
option:
/*eslint camelcase: ["error", {allow: ["UNSAFE_componentWillMount"]}]*/
function UNSAFE_componentWillMount() {
// ...
}
/*eslint camelcase: ["error", {allow: ["^UNSAFE_"]}]*/
function UNSAFE_componentWillMount() {
// ...
}
function UNSAFE_componentWillMount() {
// ...
}
When Not To Use It
If you have established coding standards using a different naming convention (separating words with underscores), turn this rule off. Source: http://eslint.org/docs/rules/
A space is required before '}'. Open
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
A space is required after '{'. Open
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
All 'var' declarations must be at the top of the function scope. Open
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Require Variable Declarations to be at the top of their scope (vars-on-top)
The vars-on-top
rule generates warnings when variable declarations are not used serially at the top of a function scope or the top of a program.
By default variable declarations are always moved (“hoisted”) invisibly to the top of their containing scope by the JavaScript interpreter.
This rule forces the programmer to represent that behavior by manually moving the variable declaration to the top of its containing scope.
Rule Details
This rule aims to keep all variable declarations in the leading series of statements. Allowing multiple declarations helps promote maintainability and is thus allowed.
Examples of incorrect code for this rule:
/*eslint vars-on-top: "error"*/
// Variable declarations in a block:
function doSomething() {
var first;
if (true) {
first = true;
}
var second;
}
// Variable declaration in for initializer:
function doSomething() {
for (var i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
// Variables after other statements:
f();
var a;
Examples of correct code for this rule:
/*eslint vars-on-top: "error"*/
function doSomething() {
var first;
var second; //multiple declarations are allowed at the top
if (true) {
first = true;
}
}
function doSomething() {
var i;
for (i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
var a;
f();
/*eslint vars-on-top: "error"*/
// Directives may precede variable declarations.
"use strict";
var a;
f();
// Comments can describe variables.
function doSomething() {
// this is the first var.
var first;
// this is the second var.
var second
}
Further Reading
All 'var' declarations must be at the top of the function scope. Open
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Require Variable Declarations to be at the top of their scope (vars-on-top)
The vars-on-top
rule generates warnings when variable declarations are not used serially at the top of a function scope or the top of a program.
By default variable declarations are always moved (“hoisted”) invisibly to the top of their containing scope by the JavaScript interpreter.
This rule forces the programmer to represent that behavior by manually moving the variable declaration to the top of its containing scope.
Rule Details
This rule aims to keep all variable declarations in the leading series of statements. Allowing multiple declarations helps promote maintainability and is thus allowed.
Examples of incorrect code for this rule:
/*eslint vars-on-top: "error"*/
// Variable declarations in a block:
function doSomething() {
var first;
if (true) {
first = true;
}
var second;
}
// Variable declaration in for initializer:
function doSomething() {
for (var i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
// Variables after other statements:
f();
var a;
Examples of correct code for this rule:
/*eslint vars-on-top: "error"*/
function doSomething() {
var first;
var second; //multiple declarations are allowed at the top
if (true) {
first = true;
}
}
function doSomething() {
var i;
for (i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
var a;
f();
/*eslint vars-on-top: "error"*/
// Directives may precede variable declarations.
"use strict";
var a;
f();
// Comments can describe variables.
function doSomething() {
// this is the first var.
var first;
// this is the second var.
var second
}
Further Reading
Unexpected string concatenation. Open
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Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
A space is required before '}'. Open
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var shortId = pieces[pieces.length - 1];
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
All 'var' declarations must be at the top of the function scope. Open
var url = '/report/menu_field_changed/?tree=' + encodeURIComponent(serialized);
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Require Variable Declarations to be at the top of their scope (vars-on-top)
The vars-on-top
rule generates warnings when variable declarations are not used serially at the top of a function scope or the top of a program.
By default variable declarations are always moved (“hoisted”) invisibly to the top of their containing scope by the JavaScript interpreter.
This rule forces the programmer to represent that behavior by manually moving the variable declaration to the top of its containing scope.
Rule Details
This rule aims to keep all variable declarations in the leading series of statements. Allowing multiple declarations helps promote maintainability and is thus allowed.
Examples of incorrect code for this rule:
/*eslint vars-on-top: "error"*/
// Variable declarations in a block:
function doSomething() {
var first;
if (true) {
first = true;
}
var second;
}
// Variable declaration in for initializer:
function doSomething() {
for (var i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
// Variables after other statements:
f();
var a;
Examples of correct code for this rule:
/*eslint vars-on-top: "error"*/
function doSomething() {
var first;
var second; //multiple declarations are allowed at the top
if (true) {
first = true;
}
}
function doSomething() {
var i;
for (i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
var a;
f();
/*eslint vars-on-top: "error"*/
// Directives may precede variable declarations.
"use strict";
var a;
f();
// Comments can describe variables.
function doSomething() {
// this is the first var.
var first;
// this is the second var.
var second
}
Further Reading
Unexpected string concatenation. Open
var url = '/report/menu_field_changed/?tree=' + encodeURIComponent(serialized);
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Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
Missing semicolon. Open
}
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
Unexpected parentheses around single function argument having a body with no curly braces. Open
.filter((entry) => (entry.state && entry.state.checked))
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Require parens in arrow function arguments (arrow-parens)
Arrow functions can omit parentheses when they have exactly one parameter. In all other cases the parameter(s) must be wrapped in parentheses. This rule enforces the consistent use of parentheses in arrow functions.
Rule Details
This rule enforces parentheses around arrow function parameters regardless of arity. For example:
/*eslint-env es6*/
// Bad
a => {}
// Good
(a) => {}
Following this style will help you find arrow functions (=>
) which may be mistakenly included in a condition
when a comparison such as >=
was the intent.
/*eslint-env es6*/
// Bad
if (a => 2) {
}
// Good
if (a >= 2) {
}
The rule can also be configured to discourage the use of parens when they are not required:
/*eslint-env es6*/
// Bad
(a) => {}
// Good
a => {}
Options
This rule has a string option and an object one.
String options are:
-
"always"
(default) requires parens around arguments in all cases. -
"as-needed"
allows omitting parens when there is only one argument.
Object properties for variants of the "as-needed"
option:
-
"requireForBlockBody": true
modifies the as-needed rule in order to require parens if the function body is in an instructions block (surrounded by braces).
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint arrow-parens: ["error", "always"]*/
/*eslint-env es6*/
a => {};
a => a;
a => {'\n'};
a.then(foo => {});
a.then(foo => a);
a(foo => { if (true) {} });
Examples of correct code for this rule with the default "always"
option:
/*eslint arrow-parens: ["error", "always"]*/
/*eslint-env es6*/
() => {};
(a) => {};
(a) => a;
(a) => {'\n'}
a.then((foo) => {});
a.then((foo) => { if (true) {} });
If Statements
One of benefits of this option is that it prevents the incorrect use of arrow functions in conditionals:
/*eslint-env es6*/
var a = 1;
var b = 2;
// ...
if (a => b) {
console.log('bigger');
} else {
console.log('smaller');
}
// outputs 'bigger', not smaller as expected
The contents of the if
statement is an arrow function, not a comparison.
If the arrow function is intentional, it should be wrapped in parens to remove ambiguity.
/*eslint-env es6*/
var a = 1;
var b = 0;
// ...
if ((a) => b) {
console.log('truthy value returned');
} else {
console.log('falsey value returned');
}
// outputs 'truthy value returned'
The following is another example of this behavior:
/*eslint-env es6*/
var a = 1, b = 2, c = 3, d = 4;
var f = a => b ? c: d;
// f = ?
f
is an arrow function which takes a
as an argument and returns the result of b ? c: d
.
This should be rewritten like so:
/*eslint-env es6*/
var a = 1, b = 2, c = 3, d = 4;
var f = (a) => b ? c: d;
as-needed
Examples of incorrect code for this rule with the "as-needed"
option:
/*eslint arrow-parens: ["error", "as-needed"]*/
/*eslint-env es6*/
(a) => {};
(a) => a;
(a) => {'\n'};
a.then((foo) => {});
a.then((foo) => a);
a((foo) => { if (true) {} });
Examples of correct code for this rule with the "as-needed"
option:
/*eslint arrow-parens: ["error", "as-needed"]*/
/*eslint-env es6*/
() => {};
a => {};
a => a;
a => {'\n'};
a.then(foo => {});
a.then(foo => { if (true) {} });
(a, b, c) => a;
(a = 10) => a;
([a, b]) => a;
({a, b}) => a;
requireForBlockBody
Examples of incorrect code for the { "requireForBlockBody": true }
option:
/*eslint arrow-parens: [2, "as-needed", { "requireForBlockBody": true }]*/
/*eslint-env es6*/
(a) => a;
a => {};
a => {'\n'};
a.map((x) => x * x);
a.map(x => {
return x * x;
});
a.then(foo => {});
Examples of correct code for the { "requireForBlockBody": true }
option:
/*eslint arrow-parens: [2, "as-needed", { "requireForBlockBody": true }]*/
/*eslint-env es6*/
(a) => {};
(a) => {'\n'};
a => ({});
() => {};
a => a;
a.then((foo) => {});
a.then((foo) => { if (true) {} });
a((foo) => { if (true) {} });
(a, b, c) => a;
(a = 10) => a;
([a, b]) => a;
({a, b}) => a;
Further Reading
- The
"as-needed", { "requireForBlockBody": true }
rule is directly inspired by the Airbnb JS Style Guide. Source: http://eslint.org/docs/rules/
A space is required before '}'. Open
miqJqueryRequest(url, {data: {all_checked: selectedKeys}});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Missing semicolon. Open
}
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
Missing semicolon. Open
}
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
All 'var' declarations must be at the top of the function scope. Open
var node = miqTreeFindNodeByKey(tree, key);
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Require Variable Declarations to be at the top of their scope (vars-on-top)
The vars-on-top
rule generates warnings when variable declarations are not used serially at the top of a function scope or the top of a program.
By default variable declarations are always moved (“hoisted”) invisibly to the top of their containing scope by the JavaScript interpreter.
This rule forces the programmer to represent that behavior by manually moving the variable declaration to the top of its containing scope.
Rule Details
This rule aims to keep all variable declarations in the leading series of statements. Allowing multiple declarations helps promote maintainability and is thus allowed.
Examples of incorrect code for this rule:
/*eslint vars-on-top: "error"*/
// Variable declarations in a block:
function doSomething() {
var first;
if (true) {
first = true;
}
var second;
}
// Variable declaration in for initializer:
function doSomething() {
for (var i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
// Variables after other statements:
f();
var a;
Examples of correct code for this rule:
/*eslint vars-on-top: "error"*/
function doSomething() {
var first;
var second; //multiple declarations are allowed at the top
if (true) {
first = true;
}
}
function doSomething() {
var i;
for (i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
var a;
f();
/*eslint vars-on-top: "error"*/
// Directives may precede variable declarations.
"use strict";
var a;
f();
// Comments can describe variables.
function doSomething() {
// this is the first var.
var first;
// this is the second var.
var second
}
Further Reading
Missing semicolon. Open
}
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
miqJqueryRequest('/' + ManageIQ.controller + '/tree_select/?id=' + encodeURIComponent(id) + '&tree=' + tree, {beforeSend: true});
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Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
Expected property shorthand. Open
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Require Object Literal Shorthand Syntax (object-shorthand)
ECMAScript 6 provides a concise form for defining object literal methods and properties. This syntax can make defining complex object literals much cleaner.
Here are a few common examples using the ES5 syntax:
// properties
var foo = {
x: x,
y: y,
z: z,
};
// methods
var foo = {
a: function() {},
b: function() {}
};
Now here are ES6 equivalents:
/*eslint-env es6*/
// properties
var foo = {x, y, z};
// methods
var foo = {
a() {},
b() {}
};
Rule Details
This rule enforces the use of the shorthand syntax. This applies to all methods (including generators) defined in object literals and any properties defined where the key name matches name of the assigned variable.
Each of the following properties would warn:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
w: function() {},
x: function *() {},
[y]: function() {},
z: z
};
In that case the expected syntax would have been:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
w() {},
*x() {},
[y]() {},
z
};
This rule does not flag arrow functions inside of object literals. The following will not warn:
/*eslint object-shorthand: "error"*/
/*eslint-env es6*/
var foo = {
x: (y) => y
};
See Also:
-
no-useless-rename
which disallows renaming import, export, and destructured assignments to the same name.
Options
The rule takes an option which specifies when it should be applied. It can be set to one of the following values:
-
"always"
(default) expects that the shorthand will be used whenever possible. -
"methods"
ensures the method shorthand is used (also applies to generators). -
"properties"
ensures the property shorthand is used (where the key and variable name match). -
"never"
ensures that no property or method shorthand is used in any object literal. -
"consistent"
ensures that either all shorthand or all long-form will be used in an object literal. -
"consistent-as-needed"
ensures that either all shorthand or all long-form will be used in an object literal, but ensures all shorthand whenever possible.
You can set the option in configuration like this:
{
"object-shorthand": ["error", "always"]
}
Additionally, the rule takes an optional object configuration:
-
"avoidQuotes": true
indicates that long-form syntax is preferred whenever the object key is a string literal (default:false
). Note that this option can only be enabled when the string option is set to"always"
,"methods"
, or"properties"
. -
"ignoreConstructors": true
can be used to prevent the rule from reporting errors for constructor functions. (By default, the rule treats constructors the same way as other functions.) Note that this option can only be enabled when the string option is set to"always"
or"methods"
. -
"avoidExplicitReturnArrows": true
indicates that methods are preferred over explicit-return arrow functions for function properties. (By default, the rule allows either of these.) Note that this option can only be enabled when the string option is set to"always"
or"methods"
.
avoidQuotes
{
"object-shorthand": ["error", "always", { "avoidQuotes": true }]
}
Example of incorrect code for this rule with the "always", { "avoidQuotes": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidQuotes": true }]*/
/*eslint-env es6*/
var foo = {
"bar-baz"() {}
};
Example of correct code for this rule with the "always", { "avoidQuotes": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidQuotes": true }]*/
/*eslint-env es6*/
var foo = {
"bar-baz": function() {},
"qux": qux
};
ignoreConstructors
{
"object-shorthand": ["error", "always", { "ignoreConstructors": true }]
}
Example of correct code for this rule with the "always", { "ignoreConstructors": true }
option:
/*eslint object-shorthand: ["error", "always", { "ignoreConstructors": true }]*/
/*eslint-env es6*/
var foo = {
ConstructorFunction: function() {}
};
avoidExplicitReturnArrows
{
"object-shorthand": ["error", "always", { "avoidExplicitReturnArrows": true }]
}
Example of incorrect code for this rule with the "always", { "avoidExplicitReturnArrows": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidExplicitReturnArrows": true }]*/
/*eslint-env es6*/
var foo = {
foo: (bar, baz) => {
return bar + baz;
},
qux: (foobar) => {
return foobar * 2;
}
};
Example of correct code for this rule with the "always", { "avoidExplicitReturnArrows": true }
option:
/*eslint object-shorthand: ["error", "always", { "avoidExplicitReturnArrows": true }]*/
/*eslint-env es6*/
var foo = {
foo(bar, baz) {
return bar + baz;
},
qux: foobar => foobar * 2
};
Example of incorrect code for this rule with the "consistent"
option:
/*eslint object-shorthand: [2, "consistent"]*/
/*eslint-env es6*/
var foo = {
a,
b: "foo",
};
Examples of correct code for this rule with the "consistent"
option:
/*eslint object-shorthand: [2, "consistent"]*/
/*eslint-env es6*/
var foo = {
a: a,
b: "foo"
};
var bar = {
a,
b,
};
Example of incorrect code with the "consistent-as-needed"
option, which is very similar to "consistent"
:
/*eslint object-shorthand: [2, "consistent-as-needed"]*/
/*eslint-env es6*/
var foo = {
a: a,
b: b,
};
When Not To Use It
Anyone not yet in an ES6 environment would not want to apply this rule. Others may find the terseness of the shorthand syntax harder to read and may not want to encourage it with this rule.
Further Reading
Object initializer - MDN Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
All 'var' declarations must be at the top of the function scope. Open
var node = miqTreeFindNodeByKey(tree, key);
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Require Variable Declarations to be at the top of their scope (vars-on-top)
The vars-on-top
rule generates warnings when variable declarations are not used serially at the top of a function scope or the top of a program.
By default variable declarations are always moved (“hoisted”) invisibly to the top of their containing scope by the JavaScript interpreter.
This rule forces the programmer to represent that behavior by manually moving the variable declaration to the top of its containing scope.
Rule Details
This rule aims to keep all variable declarations in the leading series of statements. Allowing multiple declarations helps promote maintainability and is thus allowed.
Examples of incorrect code for this rule:
/*eslint vars-on-top: "error"*/
// Variable declarations in a block:
function doSomething() {
var first;
if (true) {
first = true;
}
var second;
}
// Variable declaration in for initializer:
function doSomething() {
for (var i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
// Variables after other statements:
f();
var a;
Examples of correct code for this rule:
/*eslint vars-on-top: "error"*/
function doSomething() {
var first;
var second; //multiple declarations are allowed at the top
if (true) {
first = true;
}
}
function doSomething() {
var i;
for (i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
var a;
f();
/*eslint vars-on-top: "error"*/
// Directives may precede variable declarations.
"use strict";
var a;
f();
// Comments can describe variables.
function doSomething() {
// this is the first var.
var first;
// this is the second var.
var second
}
Further Reading
All 'var' declarations must be at the top of the function scope. Open
var node = miqTreeFindNodeByKey(treename, key);
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Require Variable Declarations to be at the top of their scope (vars-on-top)
The vars-on-top
rule generates warnings when variable declarations are not used serially at the top of a function scope or the top of a program.
By default variable declarations are always moved (“hoisted”) invisibly to the top of their containing scope by the JavaScript interpreter.
This rule forces the programmer to represent that behavior by manually moving the variable declaration to the top of its containing scope.
Rule Details
This rule aims to keep all variable declarations in the leading series of statements. Allowing multiple declarations helps promote maintainability and is thus allowed.
Examples of incorrect code for this rule:
/*eslint vars-on-top: "error"*/
// Variable declarations in a block:
function doSomething() {
var first;
if (true) {
first = true;
}
var second;
}
// Variable declaration in for initializer:
function doSomething() {
for (var i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
// Variables after other statements:
f();
var a;
Examples of correct code for this rule:
/*eslint vars-on-top: "error"*/
function doSomething() {
var first;
var second; //multiple declarations are allowed at the top
if (true) {
first = true;
}
}
function doSomething() {
var i;
for (i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
var a;
f();
/*eslint vars-on-top: "error"*/
// Directives may precede variable declarations.
"use strict";
var a;
f();
// Comments can describe variables.
function doSomething() {
// this is the first var.
var first;
// this is the second var.
var second
}
Further Reading
All 'var' declarations must be at the top of the function scope. Open
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Require Variable Declarations to be at the top of their scope (vars-on-top)
The vars-on-top
rule generates warnings when variable declarations are not used serially at the top of a function scope or the top of a program.
By default variable declarations are always moved (“hoisted”) invisibly to the top of their containing scope by the JavaScript interpreter.
This rule forces the programmer to represent that behavior by manually moving the variable declaration to the top of its containing scope.
Rule Details
This rule aims to keep all variable declarations in the leading series of statements. Allowing multiple declarations helps promote maintainability and is thus allowed.
Examples of incorrect code for this rule:
/*eslint vars-on-top: "error"*/
// Variable declarations in a block:
function doSomething() {
var first;
if (true) {
first = true;
}
var second;
}
// Variable declaration in for initializer:
function doSomething() {
for (var i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
// Variables after other statements:
f();
var a;
Examples of correct code for this rule:
/*eslint vars-on-top: "error"*/
function doSomething() {
var first;
var second; //multiple declarations are allowed at the top
if (true) {
first = true;
}
}
function doSomething() {
var i;
for (i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
var a;
f();
/*eslint vars-on-top: "error"*/
// Directives may precede variable declarations.
"use strict";
var a;
f();
// Comments can describe variables.
function doSomething() {
// this is the first var.
var first;
// this is the second var.
var second
}
Further Reading
Unexpected var, use let or const instead. Open
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
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Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
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Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
A space is required before '}'. Open
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Missing semicolon. Open
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
All 'var' declarations must be at the top of the function scope. Open
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Require Variable Declarations to be at the top of their scope (vars-on-top)
The vars-on-top
rule generates warnings when variable declarations are not used serially at the top of a function scope or the top of a program.
By default variable declarations are always moved (“hoisted”) invisibly to the top of their containing scope by the JavaScript interpreter.
This rule forces the programmer to represent that behavior by manually moving the variable declaration to the top of its containing scope.
Rule Details
This rule aims to keep all variable declarations in the leading series of statements. Allowing multiple declarations helps promote maintainability and is thus allowed.
Examples of incorrect code for this rule:
/*eslint vars-on-top: "error"*/
// Variable declarations in a block:
function doSomething() {
var first;
if (true) {
first = true;
}
var second;
}
// Variable declaration in for initializer:
function doSomething() {
for (var i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
// Variables after other statements:
f();
var a;
Examples of correct code for this rule:
/*eslint vars-on-top: "error"*/
function doSomething() {
var first;
var second; //multiple declarations are allowed at the top
if (true) {
first = true;
}
}
function doSomething() {
var i;
for (i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
var a;
f();
/*eslint vars-on-top: "error"*/
// Directives may precede variable declarations.
"use strict";
var a;
f();
// Comments can describe variables.
function doSomething() {
// this is the first var.
var first;
// this is the second var.
var second
}
Further Reading
A space is required after '{'. Open
miqJqueryRequest(url, {beforeSend: true});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
A space is required after '{'. Open
ManageIQ.redux.store.dispatch({namespace: tree, type: '@@tree/scrollToNode', key: key});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
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Require CamelCase (camelcase)
When it comes to naming variables, style guides generally fall into one of two camps: camelcase (variableName
) and underscores (variable_name
). This rule focuses on using the camelcase approach. If your style guide calls for camelCasing your variable names, then this rule is for you!
Rule Details
This rule looks for any underscores (_
) located within the source code. It ignores leading and trailing underscores and only checks those in the middle of a variable name. If ESLint decides that the variable is a constant (all uppercase), then no warning will be thrown. Otherwise, a warning will be thrown. This rule only flags definitions and assignments but not function calls. In case of ES6 import
statements, this rule only targets the name of the variable that will be imported into the local module scope.
Options
This rule has an object option:
-
"properties": "always"
(default) enforces camelcase style for property names -
"properties": "never"
does not check property names -
"ignoreDestructuring": false
(default) enforces camelcase style for destructured identifiers -
"ignoreDestructuring": true
does not check destructured identifiers -
allow
(string[]
) list of properties to accept. Accept regex.
properties: "always"
Examples of incorrect code for this rule with the default { "properties": "always" }
option:
/*eslint camelcase: "error"*/
import { no_camelcased } from "external-module"
var my_favorite_color = "#112C85";
function do_something() {
// ...
}
obj.do_something = function() {
// ...
};
function foo({ no_camelcased }) {
// ...
};
function foo({ isCamelcased: no_camelcased }) {
// ...
}
function foo({ no_camelcased = 'default value' }) {
// ...
};
var obj = {
my_pref: 1
};
var { category_id = 1 } = query;
var { foo: no_camelcased } = bar;
var { foo: bar_baz = 1 } = quz;
Examples of correct code for this rule with the default { "properties": "always" }
option:
/*eslint camelcase: "error"*/
import { no_camelcased as camelCased } from "external-module";
var myFavoriteColor = "#112C85";
var _myFavoriteColor = "#112C85";
var myFavoriteColor_ = "#112C85";
var MY_FAVORITE_COLOR = "#112C85";
var foo = bar.baz_boom;
var foo = { qux: bar.baz_boom };
obj.do_something();
do_something();
new do_something();
var { category_id: category } = query;
function foo({ isCamelCased }) {
// ...
};
function foo({ isCamelCased: isAlsoCamelCased }) {
// ...
}
function foo({ isCamelCased = 'default value' }) {
// ...
};
var { categoryId = 1 } = query;
var { foo: isCamelCased } = bar;
var { foo: isCamelCased = 1 } = quz;
properties: "never"
Examples of correct code for this rule with the { "properties": "never" }
option:
/*eslint camelcase: ["error", {properties: "never"}]*/
var obj = {
my_pref: 1
};
ignoreDestructuring: false
Examples of incorrect code for this rule with the default { "ignoreDestructuring": false }
option:
/*eslint camelcase: "error"*/
var { category_id } = query;
var { category_id = 1 } = query;
var { category_id: category_id } = query;
var { category_id: category_alias } = query;
var { category_id: categoryId, ...other_props } = query;
ignoreDestructuring: true
Examples of incorrect code for this rule with the { "ignoreDestructuring": true }
option:
/*eslint camelcase: ["error", {ignoreDestructuring: true}]*/
var { category_id: category_alias } = query;
var { category_id, ...other_props } = query;
Examples of correct code for this rule with the { "ignoreDestructuring": true }
option:
/*eslint camelcase: ["error", {ignoreDestructuring: true}]*/
var { category_id } = query;
var { category_id = 1 } = query;
var { category_id: category_id } = query;
allow
Examples of correct code for this rule with the allow
option:
/*eslint camelcase: ["error", {allow: ["UNSAFE_componentWillMount"]}]*/
function UNSAFE_componentWillMount() {
// ...
}
/*eslint camelcase: ["error", {allow: ["^UNSAFE_"]}]*/
function UNSAFE_componentWillMount() {
// ...
}
function UNSAFE_componentWillMount() {
// ...
}
When Not To Use It
If you have established coding standards using a different naming convention (separating words with underscores), turn this rule off. Source: http://eslint.org/docs/rules/
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Missing semicolon. Open
}
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
All 'var' declarations must be at the top of the function scope. Open
var text = $(elem).text().trim();
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Require Variable Declarations to be at the top of their scope (vars-on-top)
The vars-on-top
rule generates warnings when variable declarations are not used serially at the top of a function scope or the top of a program.
By default variable declarations are always moved (“hoisted”) invisibly to the top of their containing scope by the JavaScript interpreter.
This rule forces the programmer to represent that behavior by manually moving the variable declaration to the top of its containing scope.
Rule Details
This rule aims to keep all variable declarations in the leading series of statements. Allowing multiple declarations helps promote maintainability and is thus allowed.
Examples of incorrect code for this rule:
/*eslint vars-on-top: "error"*/
// Variable declarations in a block:
function doSomething() {
var first;
if (true) {
first = true;
}
var second;
}
// Variable declaration in for initializer:
function doSomething() {
for (var i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
// Variables after other statements:
f();
var a;
Examples of correct code for this rule:
/*eslint vars-on-top: "error"*/
function doSomething() {
var first;
var second; //multiple declarations are allowed at the top
if (true) {
first = true;
}
}
function doSomething() {
var i;
for (i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
var a;
f();
/*eslint vars-on-top: "error"*/
// Directives may precede variable declarations.
"use strict";
var a;
f();
// Comments can describe variables.
function doSomething() {
// this is the first var.
var first;
// this is the second var.
var second
}
Further Reading
Unexpected string concatenation. Open
elem.attr('id', 'folder' + count);
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Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
A space is required before '}'. Open
miqJqueryRequest(url, {beforeSend: true, complete: true, no_encoding: true});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var to_remove = [];
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
sessionStorage.removeItem('tree_state_' + tree);
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Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
Missing semicolon. Open
}
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- Exclude checks
require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
A space is required after '{'. Open
ManageIQ.redux.store.dispatch({namespace: tree, type: '@@tree/selectNodeSilent', key: key});
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var node = miqTreeFindNodeByKey(treename, selected_node);
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
A space is required before '}'. Open
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Identifier 'selected_node' is not in camel case. Open
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Require CamelCase (camelcase)
When it comes to naming variables, style guides generally fall into one of two camps: camelcase (variableName
) and underscores (variable_name
). This rule focuses on using the camelcase approach. If your style guide calls for camelCasing your variable names, then this rule is for you!
Rule Details
This rule looks for any underscores (_
) located within the source code. It ignores leading and trailing underscores and only checks those in the middle of a variable name. If ESLint decides that the variable is a constant (all uppercase), then no warning will be thrown. Otherwise, a warning will be thrown. This rule only flags definitions and assignments but not function calls. In case of ES6 import
statements, this rule only targets the name of the variable that will be imported into the local module scope.
Options
This rule has an object option:
-
"properties": "always"
(default) enforces camelcase style for property names -
"properties": "never"
does not check property names -
"ignoreDestructuring": false
(default) enforces camelcase style for destructured identifiers -
"ignoreDestructuring": true
does not check destructured identifiers -
allow
(string[]
) list of properties to accept. Accept regex.
properties: "always"
Examples of incorrect code for this rule with the default { "properties": "always" }
option:
/*eslint camelcase: "error"*/
import { no_camelcased } from "external-module"
var my_favorite_color = "#112C85";
function do_something() {
// ...
}
obj.do_something = function() {
// ...
};
function foo({ no_camelcased }) {
// ...
};
function foo({ isCamelcased: no_camelcased }) {
// ...
}
function foo({ no_camelcased = 'default value' }) {
// ...
};
var obj = {
my_pref: 1
};
var { category_id = 1 } = query;
var { foo: no_camelcased } = bar;
var { foo: bar_baz = 1 } = quz;
Examples of correct code for this rule with the default { "properties": "always" }
option:
/*eslint camelcase: "error"*/
import { no_camelcased as camelCased } from "external-module";
var myFavoriteColor = "#112C85";
var _myFavoriteColor = "#112C85";
var myFavoriteColor_ = "#112C85";
var MY_FAVORITE_COLOR = "#112C85";
var foo = bar.baz_boom;
var foo = { qux: bar.baz_boom };
obj.do_something();
do_something();
new do_something();
var { category_id: category } = query;
function foo({ isCamelCased }) {
// ...
};
function foo({ isCamelCased: isAlsoCamelCased }) {
// ...
}
function foo({ isCamelCased = 'default value' }) {
// ...
};
var { categoryId = 1 } = query;
var { foo: isCamelCased } = bar;
var { foo: isCamelCased = 1 } = quz;
properties: "never"
Examples of correct code for this rule with the { "properties": "never" }
option:
/*eslint camelcase: ["error", {properties: "never"}]*/
var obj = {
my_pref: 1
};
ignoreDestructuring: false
Examples of incorrect code for this rule with the default { "ignoreDestructuring": false }
option:
/*eslint camelcase: "error"*/
var { category_id } = query;
var { category_id = 1 } = query;
var { category_id: category_id } = query;
var { category_id: category_alias } = query;
var { category_id: categoryId, ...other_props } = query;
ignoreDestructuring: true
Examples of incorrect code for this rule with the { "ignoreDestructuring": true }
option:
/*eslint camelcase: ["error", {ignoreDestructuring: true}]*/
var { category_id: category_alias } = query;
var { category_id, ...other_props } = query;
Examples of correct code for this rule with the { "ignoreDestructuring": true }
option:
/*eslint camelcase: ["error", {ignoreDestructuring: true}]*/
var { category_id } = query;
var { category_id = 1 } = query;
var { category_id: category_id } = query;
allow
Examples of correct code for this rule with the allow
option:
/*eslint camelcase: ["error", {allow: ["UNSAFE_componentWillMount"]}]*/
function UNSAFE_componentWillMount() {
// ...
}
/*eslint camelcase: ["error", {allow: ["^UNSAFE_"]}]*/
function UNSAFE_componentWillMount() {
// ...
}
function UNSAFE_componentWillMount() {
// ...
}
When Not To Use It
If you have established coding standards using a different naming convention (separating words with underscores), turn this rule off. Source: http://eslint.org/docs/rules/
Missing semicolon. Open
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
A space is required before '}'. Open
miqTreeObject(treename).revealNode(node, {silent: true});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var nodePos = node.$el.offset().top - parentPanelBody.offset().top;
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var selectedKeys = [];
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var ids = id.split('|')[0].split('_'); // Break apart the node ids
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected parentheses around single function argument having a body with no curly braces. Open
window.miqGetSelectedKeys = (tree) => Object.values(tree)
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Require parens in arrow function arguments (arrow-parens)
Arrow functions can omit parentheses when they have exactly one parameter. In all other cases the parameter(s) must be wrapped in parentheses. This rule enforces the consistent use of parentheses in arrow functions.
Rule Details
This rule enforces parentheses around arrow function parameters regardless of arity. For example:
/*eslint-env es6*/
// Bad
a => {}
// Good
(a) => {}
Following this style will help you find arrow functions (=>
) which may be mistakenly included in a condition
when a comparison such as >=
was the intent.
/*eslint-env es6*/
// Bad
if (a => 2) {
}
// Good
if (a >= 2) {
}
The rule can also be configured to discourage the use of parens when they are not required:
/*eslint-env es6*/
// Bad
(a) => {}
// Good
a => {}
Options
This rule has a string option and an object one.
String options are:
-
"always"
(default) requires parens around arguments in all cases. -
"as-needed"
allows omitting parens when there is only one argument.
Object properties for variants of the "as-needed"
option:
-
"requireForBlockBody": true
modifies the as-needed rule in order to require parens if the function body is in an instructions block (surrounded by braces).
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint arrow-parens: ["error", "always"]*/
/*eslint-env es6*/
a => {};
a => a;
a => {'\n'};
a.then(foo => {});
a.then(foo => a);
a(foo => { if (true) {} });
Examples of correct code for this rule with the default "always"
option:
/*eslint arrow-parens: ["error", "always"]*/
/*eslint-env es6*/
() => {};
(a) => {};
(a) => a;
(a) => {'\n'}
a.then((foo) => {});
a.then((foo) => { if (true) {} });
If Statements
One of benefits of this option is that it prevents the incorrect use of arrow functions in conditionals:
/*eslint-env es6*/
var a = 1;
var b = 2;
// ...
if (a => b) {
console.log('bigger');
} else {
console.log('smaller');
}
// outputs 'bigger', not smaller as expected
The contents of the if
statement is an arrow function, not a comparison.
If the arrow function is intentional, it should be wrapped in parens to remove ambiguity.
/*eslint-env es6*/
var a = 1;
var b = 0;
// ...
if ((a) => b) {
console.log('truthy value returned');
} else {
console.log('falsey value returned');
}
// outputs 'truthy value returned'
The following is another example of this behavior:
/*eslint-env es6*/
var a = 1, b = 2, c = 3, d = 4;
var f = a => b ? c: d;
// f = ?
f
is an arrow function which takes a
as an argument and returns the result of b ? c: d
.
This should be rewritten like so:
/*eslint-env es6*/
var a = 1, b = 2, c = 3, d = 4;
var f = (a) => b ? c: d;
as-needed
Examples of incorrect code for this rule with the "as-needed"
option:
/*eslint arrow-parens: ["error", "as-needed"]*/
/*eslint-env es6*/
(a) => {};
(a) => a;
(a) => {'\n'};
a.then((foo) => {});
a.then((foo) => a);
a((foo) => { if (true) {} });
Examples of correct code for this rule with the "as-needed"
option:
/*eslint arrow-parens: ["error", "as-needed"]*/
/*eslint-env es6*/
() => {};
a => {};
a => a;
a => {'\n'};
a.then(foo => {});
a.then(foo => { if (true) {} });
(a, b, c) => a;
(a = 10) => a;
([a, b]) => a;
({a, b}) => a;
requireForBlockBody
Examples of incorrect code for the { "requireForBlockBody": true }
option:
/*eslint arrow-parens: [2, "as-needed", { "requireForBlockBody": true }]*/
/*eslint-env es6*/
(a) => a;
a => {};
a => {'\n'};
a.map((x) => x * x);
a.map(x => {
return x * x;
});
a.then(foo => {});
Examples of correct code for the { "requireForBlockBody": true }
option:
/*eslint arrow-parens: [2, "as-needed", { "requireForBlockBody": true }]*/
/*eslint-env es6*/
(a) => {};
(a) => {'\n'};
a => ({});
() => {};
a => a;
a.then((foo) => {});
a.then((foo) => { if (true) {} });
a((foo) => { if (true) {} });
(a, b, c) => a;
(a = 10) => a;
([a, b]) => a;
({a, b}) => a;
Further Reading
- The
"as-needed", { "requireForBlockBody": true }
rule is directly inspired by the Airbnb JS Style Guide. Source: http://eslint.org/docs/rules/
A space is required before '}'. Open
miqJqueryRequest('/' + ManageIQ.controller + '/tree_select/?id=' + encodeURIComponent(id) + '&tree=' + tree, {beforeSend: true});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var selectedKeys = miqGetSelectedKeys(tree);
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Missing semicolon. Open
}
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
A space is required after '{'. Open
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var node = miqTreeFindNodeByKey(treename, key);
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
for (var property in tree) {
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- Exclude checks
require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var items = grid.find('.panel-heading').toArray().map(function(elem) {
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
A space is required after '{'. Open
miqJqueryRequest('/' + ManageIQ.controller + '/snap_pressed/' + encodeURIComponent(shortId), {beforeSend: true, complete: true});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
All 'var' declarations must be at the top of the function scope. Open
for (var i = 0; i < to_remove.length; i++) {
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Require Variable Declarations to be at the top of their scope (vars-on-top)
The vars-on-top
rule generates warnings when variable declarations are not used serially at the top of a function scope or the top of a program.
By default variable declarations are always moved (“hoisted”) invisibly to the top of their containing scope by the JavaScript interpreter.
This rule forces the programmer to represent that behavior by manually moving the variable declaration to the top of its containing scope.
Rule Details
This rule aims to keep all variable declarations in the leading series of statements. Allowing multiple declarations helps promote maintainability and is thus allowed.
Examples of incorrect code for this rule:
/*eslint vars-on-top: "error"*/
// Variable declarations in a block:
function doSomething() {
var first;
if (true) {
first = true;
}
var second;
}
// Variable declaration in for initializer:
function doSomething() {
for (var i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
// Variables after other statements:
f();
var a;
Examples of correct code for this rule:
/*eslint vars-on-top: "error"*/
function doSomething() {
var first;
var second; //multiple declarations are allowed at the top
if (true) {
first = true;
}
}
function doSomething() {
var i;
for (i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
var a;
f();
/*eslint vars-on-top: "error"*/
// Directives may precede variable declarations.
"use strict";
var a;
f();
// Comments can describe variables.
function doSomething() {
// this is the first var.
var first;
// this is the second var.
var second
}
Further Reading
Unexpected var, use let or const instead. Open
var currId = '';
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- Exclude checks
require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Missing semicolon. Open
}
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
All 'var' declarations must be at the top of the function scope. Open
var count = grid.find('.panel-heading').length;
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Require Variable Declarations to be at the top of their scope (vars-on-top)
The vars-on-top
rule generates warnings when variable declarations are not used serially at the top of a function scope or the top of a program.
By default variable declarations are always moved (“hoisted”) invisibly to the top of their containing scope by the JavaScript interpreter.
This rule forces the programmer to represent that behavior by manually moving the variable declaration to the top of its containing scope.
Rule Details
This rule aims to keep all variable declarations in the leading series of statements. Allowing multiple declarations helps promote maintainability and is thus allowed.
Examples of incorrect code for this rule:
/*eslint vars-on-top: "error"*/
// Variable declarations in a block:
function doSomething() {
var first;
if (true) {
first = true;
}
var second;
}
// Variable declaration in for initializer:
function doSomething() {
for (var i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
// Variables after other statements:
f();
var a;
Examples of correct code for this rule:
/*eslint vars-on-top: "error"*/
function doSomething() {
var first;
var second; //multiple declarations are allowed at the top
if (true) {
first = true;
}
}
function doSomething() {
var i;
for (i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
var a;
f();
/*eslint vars-on-top: "error"*/
// Directives may precede variable declarations.
"use strict";
var a;
f();
// Comments can describe variables.
function doSomething() {
// this is the first var.
var first;
// this is the second var.
var second
}
Further Reading
All 'var' declarations must be at the top of the function scope. Open
var items = grid.find('.panel-heading').toArray().map(function(elem) {
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Require Variable Declarations to be at the top of their scope (vars-on-top)
The vars-on-top
rule generates warnings when variable declarations are not used serially at the top of a function scope or the top of a program.
By default variable declarations are always moved (“hoisted”) invisibly to the top of their containing scope by the JavaScript interpreter.
This rule forces the programmer to represent that behavior by manually moving the variable declaration to the top of its containing scope.
Rule Details
This rule aims to keep all variable declarations in the leading series of statements. Allowing multiple declarations helps promote maintainability and is thus allowed.
Examples of incorrect code for this rule:
/*eslint vars-on-top: "error"*/
// Variable declarations in a block:
function doSomething() {
var first;
if (true) {
first = true;
}
var second;
}
// Variable declaration in for initializer:
function doSomething() {
for (var i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
// Variables after other statements:
f();
var a;
Examples of correct code for this rule:
/*eslint vars-on-top: "error"*/
function doSomething() {
var first;
var second; //multiple declarations are allowed at the top
if (true) {
first = true;
}
}
function doSomething() {
var i;
for (i=0; i<10; i++) {}
}
/*eslint vars-on-top: "error"*/
var a;
f();
/*eslint vars-on-top: "error"*/
// Directives may precede variable declarations.
"use strict";
var a;
f();
// Comments can describe variables.
function doSomething() {
// this is the first var.
var first;
// this is the second var.
var second
}
Further Reading
Unexpected var, use let or const instead. Open
var serialized = JSON.stringify(items);
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- Exclude checks
require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var url = '/report/menu_field_changed/?tree=' + encodeURIComponent(serialized);
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- Exclude checks
require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var obj;
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var tree = miqTreeObject(tree);
- Read upRead up
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- Exclude checks
require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var parentPanelBody = node.$el.parents('div.panel-body');
- Read upRead up
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- Exclude checks
require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
A space is required after '{'. Open
ManageIQ.redux.store.dispatch({namespace: treename, type: '@@tree/expandAll', value: expand_mode});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
A space is required before '}'. Open
ManageIQ.redux.store.dispatch({namespace: treeName, type: '@@tree/checkAll', value: cb.checked});
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var pieces = id.split(/-/);
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require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
miqJqueryRequest('/' + ManageIQ.controller + '/ae_tree_select_toggle?button=domain');
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Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
Unexpected var, use let or const instead. Open
var selected_id = selected.children()[0].id.split('|-|');
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- Exclude checks
require let
or const
instead of var
(no-var)
ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let
and const
keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes
such as:
var count = people.length;
var enoughFood = count > sandwiches.length;
if (enoughFood) {
var count = sandwiches.length; // accidentally overriding the count variable
console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}
// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");
Rule Details
This rule is aimed at discouraging the use of var
and encouraging the use of const
or let
instead.
Examples
Examples of incorrect code for this rule:
/*eslint no-var: "error"*/
var x = "y";
var CONFIG = {};
Examples of correct code for this rule:
/*eslint no-var: "error"*/
/*eslint-env es6*/
let x = "y";
const CONFIG = {};
When Not To Use It
In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their
codebase may not want to apply this rule if the cost of migrating from var
to let
is too costly.
Source: http://eslint.org/docs/rules/
Missing semicolon. Open
}
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
A space is required after '{'. Open
miqTreeObject(treename).revealNode(node, {silent: true});
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enforce consistent spacing inside braces (object-curly-spacing)
While formatting preferences are very personal, a number of style guides require or disallow spaces between curly braces in the following situations:
// simple object literals
var obj = { foo: "bar" };
// nested object literals
var obj = { foo: { zoo: "bar" } };
// destructuring assignment (EcmaScript 6)
var { x, y } = y;
// import/export declarations (EcmaScript 6)
import { foo } from "bar";
export { foo };
Rule Details
This rule enforces consistent spacing inside braces of object literals, destructuring assignments, and import/export specifiers.
Options
This rule has two options, a string option and an object option.
String option:
-
"never"
(default) disallows spacing inside of braces -
"always"
requires spacing inside of braces (except{}
)
Object option:
-
"arraysInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set tonever
) -
"arraysInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an array element (applies when the first option is set toalways
) -
"objectsInObjects": true
requires spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set tonever
) -
"objectsInObjects": false
disallows spacing inside of braces of objects beginning and/or ending with an object element (applies when the first option is set toalways
)
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = { 'foo': 'bar' };
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux'}, bar};
var {x } = y;
import { foo } from 'bar';
Examples of correct code for this rule with the default "never"
option:
/*eslint object-curly-spacing: ["error", "never"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': {'bar': 'baz'}, 'qux': 'quxx'};
var obj = {
'foo': 'bar'
};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var obj = {};
var {x} = y;
import {foo} from 'bar';
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {'foo': 'bar'};
var obj = {'foo': 'bar' };
var obj = { baz: {'foo': 'qux'}, bar};
var obj = {baz: { 'foo': 'qux' }, bar};
var obj = {'foo': 'bar'
};
var obj = {
'foo':'bar'};
var {x} = y;
import {foo } from 'bar';
Examples of correct code for this rule with the "always"
option:
/*eslint object-curly-spacing: ["error", "always"]*/
var obj = {};
var obj = { 'foo': 'bar' };
var obj = { 'foo': { 'bar': 'baz' }, 'qux': 'quxx' };
var obj = {
'foo': 'bar'
};
var { x } = y;
import { foo } from 'bar';
arraysInObjects
Examples of additional correct code for this rule with the "never", { "arraysInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "arraysInObjects": true }]*/
var obj = {"foo": [ 1, 2 ] };
var obj = {"foo": [ "baz", "bar" ] };
Examples of additional correct code for this rule with the "always", { "arraysInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "arraysInObjects": false }]*/
var obj = { "foo": [ 1, 2 ]};
var obj = { "foo": [ "baz", "bar" ]};
objectsInObjects
Examples of additional correct code for this rule with the "never", { "objectsInObjects": true }
options:
/*eslint object-curly-spacing: ["error", "never", { "objectsInObjects": true }]*/
var obj = {"foo": {"baz": 1, "bar": 2} };
Examples of additional correct code for this rule with the "always", { "objectsInObjects": false }
options:
/*eslint object-curly-spacing: ["error", "always", { "objectsInObjects": false }]*/
var obj = { "foo": { "baz": 1, "bar": 2 }};
When Not To Use It
You can turn this rule off if you are not concerned with the consistency of spacing between curly braces.
Related Rules
- [array-bracket-spacing](array-bracket-spacing.md)
- [comma-spacing](comma-spacing.md)
- [computed-property-spacing](computed-property-spacing.md)
- [space-in-parens](space-in-parens.md) Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
var url = ManageIQ.tree.checkUrl + '?id=' + encodeURIComponent(key) + '&check=' + checked;
- Read upRead up
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- Exclude checks
Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
currId += '_' + item;
- Read upRead up
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- Exclude checks
Suggest using template literals instead of string concatenation. (prefer-template)
In ES2015 (ES6), we can use template literals instead of string concatenation.
var str = "Hello, " + name + "!";
/*eslint-env es6*/
var str = `Hello, ${name}!`;
Rule Details
This rule is aimed to flag usage of +
operators with strings.
Examples
Examples of incorrect code for this rule:
/*eslint prefer-template: "error"*/
var str = "Hello, " + name + "!";
var str = "Time: " + (12 * 60 * 60 * 1000);
Examples of correct code for this rule:
/*eslint prefer-template: "error"*/
/*eslint-env es6*/
var str = "Hello World!";
var str = `Hello, ${name}!`;
var str = `Time: ${12 * 60 * 60 * 1000}`;
// This is reported by `no-useless-concat`.
var str = "Hello, " + "World!";
When Not To Use It
This rule should not be used in ES3/5 environments.
In ES2015 (ES6) or later, if you don't want to be notified about string concatenation, you can safely disable this rule.
Related Rules
- [no-useless-concat](no-useless-concat.md)
- [quotes](quotes.md) Source: http://eslint.org/docs/rules/
Missing semicolon. Open
}
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require or disallow semicolons instead of ASI (semi)
JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:
var name = "ESLint"
var website = "eslint.org";
On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.
In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.
However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:
return
{
name: "ESLint"
};
This may look like a return
statement that returns an object literal, however, the JavaScript engine will interpret this code as:
return;
{
name: "ESLint";
}
Effectively, a semicolon is inserted after the return
statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.
On the other side of the argument are those who say that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:
var globalCounter = { }
(function () {
var n = 0
globalCounter.increment = function () {
return ++n
}
})()
In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.
Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n
character always ends a statement (just like a semicolon) unless one of the following is true:
- The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with
.
or,
.) - The line is
--
or++
(in which case it will decrement/increment the next token.) - It is a
for()
,while()
,do
,if()
, orelse
, and there is no{
- The next line starts with
[
,(
,+
,*
,/
,-
,,
,.
, or some other binary operator that can only be found between two tokens in a single expression.
Rule Details
This rule enforces consistent use of semicolons.
Options
This rule has two options, a string option and an object option.
String option:
-
"always"
(default) requires semicolons at the end of statements -
"never"
disallows semicolons as the end of statements (except to disambiguate statements beginning with[
,(
,/
,+
, or-
)
Object option (when "always"
):
-
"omitLastInOneLineBlock": true
ignores the last semicolon in a block in which its braces (and therefore the content of the block) are in the same line
Object option (when "never"
):
-
"beforeStatementContinuationChars": "any"
(default) ignores semicolons (or lacking semicolon) at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "always"
requires semicolons at the end of statements if the next line starts with[
,(
,/
,+
, or-
. -
"beforeStatementContinuationChars": "never"
disallows semicolons as the end of statements if it doesn't make ASI hazard even if the next line starts with[
,(
,/
,+
, or-
.
always
Examples of incorrect code for this rule with the default "always"
option:
/*eslint semi: ["error", "always"]*/
var name = "ESLint"
object.method = function() {
// ...
}
Examples of correct code for this rule with the default "always"
option:
/*eslint semi: "error"*/
var name = "ESLint";
object.method = function() {
// ...
};
never
Examples of incorrect code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint";
object.method = function() {
// ...
};
Examples of correct code for this rule with the "never"
option:
/*eslint semi: ["error", "never"]*/
var name = "ESLint"
object.method = function() {
// ...
}
var name = "ESLint"
;(function() {
// ...
})()
import a from "a"
(function() {
// ...
})()
import b from "b"
;(function() {
// ...
})()
omitLastInOneLineBlock
Examples of additional correct code for this rule with the "always", { "omitLastInOneLineBlock": true }
options:
/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */
if (foo) { bar() }
if (foo) { bar(); baz() }
beforeStatementContinuationChars
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "always" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "always"}] */
import a from "a"
(function() {
// ...
})()
Examples of additional incorrect code for this rule with the "never", { "beforeStatementContinuationChars": "never" }
options:
/*eslint semi: ["error", "never", { "beforeStatementContinuationChars": "never"}] */
import a from "a"
;(function() {
// ...
})()
When Not To Use It
If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.
Further Reading
Related Rules
- [no-extra-semi](no-extra-semi.md)
- [no-unexpected-multiline](no-unexpected-multiline.md)
- [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/
Unexpected function expression. Open
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Require using arrow functions for callbacks (prefer-arrow-callback)
Arrow functions can be an attractive alternative to function expressions for callbacks or function arguments.
For example, arrow functions are automatically bound to their surrounding scope/context. This provides an alternative to the pre-ES6 standard of explicitly binding function expressions to achieve similar behavior.
Additionally, arrow functions are:
less verbose, and easier to reason about.
bound lexically regardless of where or when they are invoked.
Rule Details
This rule locates function expressions used as callbacks or function arguments. An error will be produced for any that could be replaced by an arrow function without changing the result.
The following examples will be flagged:
/* eslint prefer-arrow-callback: "error" */
foo(function(a) { return a; }); // ERROR
// prefer: foo(a => a)
foo(function() { return this.a; }.bind(this)); // ERROR
// prefer: foo(() => this.a)
Instances where an arrow function would not produce identical results will be ignored.
The following examples will not be flagged:
/* eslint prefer-arrow-callback: "error" */
/* eslint-env es6 */
// arrow function callback
foo(a => a); // OK
// generator as callback
foo(function*() { yield; }); // OK
// function expression not used as callback or function argument
var foo = function foo(a) { return a; }; // OK
// unbound function expression callback
foo(function() { return this.a; }); // OK
// recursive named function callback
foo(function bar(n) { return n && n + bar(n - 1); }); // OK
Options
Access further control over this rule's behavior via an options object.
Default: { allowNamedFunctions: false, allowUnboundThis: true }
allowNamedFunctions
By default { "allowNamedFunctions": false }
, this boolean
option prohibits using named functions as callbacks or function arguments.
Changing this value to true
will reverse this option's behavior by allowing use of named functions without restriction.
{ "allowNamedFunctions": true }
will not flag the following example:
/* eslint prefer-arrow-callback: [ "error", { "allowNamedFunctions": true } ] */
foo(function bar() {});
allowUnboundThis
By default { "allowUnboundThis": true }
, this boolean
option allows function expressions containing this
to be used as callbacks, as long as the function in question has not been explicitly bound.
When set to false
this option prohibits the use of function expressions as callbacks or function arguments entirely, without exception.
{ "allowUnboundThis": false }
will flag the following examples:
/* eslint prefer-arrow-callback: [ "error", { "allowUnboundThis": false } ] */
/* eslint-env es6 */
foo(function() { this.a; });
foo(function() { (() => this); });
someArray.map(function(itm) { return this.doSomething(itm); }, someObject);
When Not To Use It
In environments that have not yet adopted ES6 language features (ES3/5).
In ES6+ environments that allow the use of function expressions when describing callbacks or function arguments.
Further Reading
Unsafe usage of ReturnStatement. Open
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disallow control flow statements in finally
blocks (no-unsafe-finally)
JavaScript suspends the control flow statements of try
and catch
blocks until the execution of finally
block finishes. So, when return
, throw
, break
, or continue
is used in finally
, control flow statements inside try
and catch
are overwritten, which is considered as unexpected behavior. Such as:
// We expect this function to return 1;
(() => {
try {
return 1; // 1 is returned but suspended until finally block ends
} catch(err) {
return 2;
} finally {
return 3; // 3 is returned before 1, which we did not expect
}
})();
// > 3
// We expect this function to throw an error, then return
(() => {
try {
throw new Error("Try"); // error is thrown but suspended until finally block ends
} finally {
return 3; // 3 is returned before the error is thrown, which we did not expect
}
})();
// > 3
// We expect this function to throw Try(...) error from the catch block
(() => {
try {
throw new Error("Try")
} catch(err) {
throw err; // The error thrown from try block is caught and rethrown
} finally {
throw new Error("Finally"); // Finally(...) is thrown, which we did not expect
}
})();
// > Uncaught Error: Finally(...)
// We expect this function to return 0 from try block.
(() => {
label: try {
return 0; // 0 is returned but suspended until finally block ends
} finally {
break label; // It breaks out the try-finally block, before 0 is returned.
}
return 1;
})();
// > 1
Rule Details
This rule disallows return
, throw
, break
, and continue
statements inside finally
blocks. It allows indirect usages, such as in function
or class
definitions.
Examples of incorrect code for this rule:
/*eslint no-unsafe-finally: "error"*/
let foo = function() {
try {
return 1;
} catch(err) {
return 2;
} finally {
return 3;
}
};
/*eslint no-unsafe-finally: "error"*/
let foo = function() {
try {
return 1;
} catch(err) {
return 2;
} finally {
throw new Error;
}
};
Examples of correct code for this rule:
/*eslint no-unsafe-finally: "error"*/
let foo = function() {
try {
return 1;
} catch(err) {
return 2;
} finally {
console.log("hola!");
}
};
/*eslint no-unsafe-finally: "error"*/
let foo = function() {
try {
return 1;
} catch(err) {
return 2;
} finally {
let a = function() {
return "hola!";
}
}
};
/*eslint no-unsafe-finally: "error"*/
let foo = function(a) {
try {
return 1;
} catch(err) {
return 2;
} finally {
switch(a) {
case 1: {
console.log("hola!")
break;
}
}
}
};
When Not To Use It
If you want to allow control flow operations in finally
blocks, you can turn this rule off.
Source: http://eslint.org/docs/rules/
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
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Disallow Unused Expressions (no-unused-expressions)
An unused expression which has no effect on the state of the program indicates a logic error.
For example, n + 1;
is not a syntax error, but it might be a typing mistake where a programmer meant an assignment statement n += 1;
instead. Sometimes, such unused expressions may be eliminated by some build tools in production environment, which possibly breaks application logic.
Rule Details
This rule aims to eliminate unused expressions which have no effect on the state of the program.
This rule does not apply to function calls or constructor calls with the new
operator, because they could have side effects on the state of the program.
var i = 0;
function increment() { i += 1; }
increment(); // return value is unused, but i changed as a side effect
var nThings = 0;
function Thing() { nThings += 1; }
new Thing(); // constructed object is unused, but nThings changed as a side effect
This rule does not apply to directives (which are in the form of literal string expressions such as "use strict";
at the beginning of a script, module, or function).
Sequence expressions (those using a comma, such as a = 1, b = 2
) are always considered unused unless their return value is assigned or used in a condition evaluation, or a function call is made with the sequence expression value.
Options
This rule, in its default state, does not require any arguments. If you would like to enable one or more of the following you may pass an object with the options set as follows:
-
allowShortCircuit
set totrue
will allow you to use short circuit evaluations in your expressions (Default:false
). -
allowTernary
set totrue
will enable you to use ternary operators in your expressions similarly to short circuit evaluations (Default:false
). -
allowTaggedTemplates
set totrue
will enable you to use tagged template literals in your expressions (Default:false
).
These options allow unused expressions only if all of the code paths either directly change the state (for example, assignment statement) or could have side effects (for example, function call).
Examples of incorrect code for the default { "allowShortCircuit": false, "allowTernary": false }
options:
/*eslint no-unused-expressions: "error"*/
0
if(0) 0
{0}
f(0), {}
a && b()
a, b()
c = a, b;
a() && function namedFunctionInExpressionContext () {f();}
(function anIncompleteIIFE () {});
injectGlobal`body{ color: red; }`
Note that one or more string expression statements (with or without semi-colons) will only be considered as unused if they are not in the beginning of a script, module, or function (alone and uninterrupted by other statements). Otherwise, they will be treated as part of a "directive prologue", a section potentially usable by JavaScript engines. This includes "strict mode" directives.
"use strict";
"use asm"
"use stricter";
"use babel"
"any other strings like this in the prologue";
Examples of correct code for the default { "allowShortCircuit": false, "allowTernary": false }
options:
/*eslint no-unused-expressions: "error"*/
{} // In this context, this is a block statement, not an object literal
{myLabel: someVar} // In this context, this is a block statement with a label and expression, not an object literal
function namedFunctionDeclaration () {}
(function aGenuineIIFE () {}());
f()
a = 0
new C
delete a.b
void a
allowShortCircuit
Examples of incorrect code for the { "allowShortCircuit": true }
option:
/*eslint no-unused-expressions: ["error", { "allowShortCircuit": true }]*/
a || b
Examples of correct code for the { "allowShortCircuit": true }
option:
/*eslint no-unused-expressions: ["error", { "allowShortCircuit": true }]*/
a && b()
a() || (b = c)
allowTernary
Examples of incorrect code for the { "allowTernary": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTernary": true }]*/
a ? b : 0
a ? b : c()
Examples of correct code for the { "allowTernary": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTernary": true }]*/
a ? b() : c()
a ? (b = c) : d()
allowShortCircuit and allowTernary
Examples of correct code for the { "allowShortCircuit": true, "allowTernary": true }
options:
/*eslint no-unused-expressions: ["error", { "allowShortCircuit": true, "allowTernary": true }]*/
a ? b() || (c = d) : e()
allowTaggedTemplates
Examples of incorrect code for the { "allowTaggedTemplates": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTaggedTemplates": true }]*/
`some untagged template string`;
Examples of correct code for the { "allowTaggedTemplates": true }
option:
/*eslint no-unused-expressions: ["error", { "allowTaggedTemplates": true }]*/
tag`some tagged template string`;
Source: http://eslint.org/docs/rules/
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
Unary operator '++' used. Open
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disallow the unary operators ++
and --
(no-plusplus)
Because the unary ++
and --
operators are subject to automatic semicolon insertion, differences in whitespace can change semantics of source code.
var i = 10;
var j = 20;
i ++
j
// i = 11, j = 20
var i = 10;
var j = 20;
i
++
j
// i = 10, j = 21
Rule Details
This rule disallows the unary operators ++
and --
.
Examples of incorrect code for this rule:
/*eslint no-plusplus: "error"*/
var foo = 0;
foo++;
var bar = 42;
bar--;
for (i = 0; i < l; i++) {
return;
}
Examples of correct code for this rule:
/*eslint no-plusplus: "error"*/
var foo = 0;
foo += 1;
var bar = 42;
bar -= 1;
for (i = 0; i < l; i += 1) {
return;
}
Options
This rule has an object option.
-
"allowForLoopAfterthoughts": true
allows unary operators++
and--
in the afterthought (final expression) of afor
loop.
allowForLoopAfterthoughts
Examples of correct code for this rule with the { "allowForLoopAfterthoughts": true }
option:
/*eslint no-plusplus: ["error", { "allowForLoopAfterthoughts": true }]*/
for (i = 0; i < l; i++) {
return;
}
for (i = 0; i < l; i--) {
return;
}
Source: http://eslint.org/docs/rules/
'miqTreeObject' is not defined. Open
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'tree' is already defined. Open
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disallow variable redeclaration (no-redeclare)
In JavaScript, it's possible to redeclare the same variable name using var
. This can lead to confusion as to where the variable is actually declared and initialized.
Rule Details
This rule is aimed at eliminating variables that have multiple declarations in the same scope.
Examples of incorrect code for this rule:
/*eslint no-redeclare: "error"*/
var a = 3;
var a = 10;
Examples of correct code for this rule:
/*eslint no-redeclare: "error"*/
var a = 3;
// ...
a = 10;
Options
This rule takes one optional argument, an object with a boolean property "builtinGlobals"
. It defaults to false
.
If set to true
, this rule also checks redeclaration of built-in globals, such as Object
, Array
, Number
...
builtinGlobals
The "builtinGlobals"
option will check for redeclaration of built-in globals in global scope.
Examples of incorrect code for the { "builtinGlobals": true }
option:
/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
var Object = 0;
Examples of incorrect code for the { "builtinGlobals": true }
option and the browser
environment:
/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/
var top = 0;
The browser
environment has many built-in global variables (for example, top
). Some of built-in global variables cannot be redeclared.
Note that when using the node
or commonjs
environments (or ecmaFeatures.globalReturn
, if using the default parser), the top scope of a program is not actually the global scope, but rather a "module" scope. When this is the case, declaring a variable named after a builtin global is not a redeclaration, but rather a shadowing of the global variable. In that case, the [no-shadow
](no-shadow.md) rule with the "builtinGlobals"
option should be used.
Related Rules
- [no-shadow](no-shadow.md) Source: http://eslint.org/docs/rules/
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
Expected '!==' and instead saw '!='. Open
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Require === and !== (eqeqeq)
It is considered good practice to use the type-safe equality operators ===
and !==
instead of their regular counterparts ==
and !=
.
The reason for this is that ==
and !=
do type coercion which follows the rather obscure Abstract Equality Comparison Algorithm.
For instance, the following statements are all considered true
:
[] == false
[] == ![]
3 == "03"
If one of those occurs in an innocent-looking statement such as a == b
the actual problem is very difficult to spot.
Rule Details
This rule is aimed at eliminating the type-unsafe equality operators.
Examples of incorrect code for this rule:
/*eslint eqeqeq: "error"*/
if (x == 42) { }
if ("" == text) { }
if (obj.getStuff() != undefined) { }
The --fix
option on the command line automatically fixes some problems reported by this rule. A problem is only fixed if one of the operands is a typeof
expression, or if both operands are literals with the same type.
Options
always
The "always"
option (default) enforces the use of ===
and !==
in every situation (except when you opt-in to more specific handling of null
[see below]).
Examples of incorrect code for the "always"
option:
/*eslint eqeqeq: ["error", "always"]*/
a == b
foo == true
bananas != 1
value == undefined
typeof foo == 'undefined'
'hello' != 'world'
0 == 0
true == true
foo == null
Examples of correct code for the "always"
option:
/*eslint eqeqeq: ["error", "always"]*/
a === b
foo === true
bananas !== 1
value === undefined
typeof foo === 'undefined'
'hello' !== 'world'
0 === 0
true === true
foo === null
This rule optionally takes a second argument, which should be an object with the following supported properties:
-
"null"
: Customize how this rule treatsnull
literals. Possible values:-
always
(default) - Always use === or !==. -
never
- Never use === or !== withnull
. -
ignore
- Do not apply this rule tonull
.
-
smart
The "smart"
option enforces the use of ===
and !==
except for these cases:
- Comparing two literal values
- Evaluating the value of
typeof
- Comparing against
null
Examples of incorrect code for the "smart"
option:
/*eslint eqeqeq: ["error", "smart"]*/
// comparing two variables requires ===
a == b
// only one side is a literal
foo == true
bananas != 1
// comparing to undefined requires ===
value == undefined
Examples of correct code for the "smart"
option:
/*eslint eqeqeq: ["error", "smart"]*/
typeof foo == 'undefined'
'hello' != 'world'
0 == 0
true == true
foo == null
allow-null
Deprecated: Instead of using this option use "always" and pass a "null" option property with value "ignore". This will tell ESLint to always enforce strict equality except when comparing with the null
literal.
["error", "always", {"null": "ignore"}]
When Not To Use It
If you don't want to enforce a style for using equality operators, then it's safe to disable this rule. Source: http://eslint.org/docs/rules/
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqTreeObject' is not defined. Open
miqTreeObject(tree).options.onNodeSelected(0, miqTreeFindNodeByKey(tree, key));
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'i' used outside of binding context. Open
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Treat var as Block Scoped (block-scoped-var)
The block-scoped-var
rule generates warnings when variables are used outside of the block in which they were defined. This emulates C-style block scope.
Rule Details
This rule aims to reduce the usage of variables outside of their binding context and emulate traditional block scope from other languages. This is to help newcomers to the language avoid difficult bugs with variable hoisting.
Examples of incorrect code for this rule:
/*eslint block-scoped-var: "error"*/
function doIf() {
if (true) {
var build = true;
}
console.log(build);
}
function doIfElse() {
if (true) {
var build = true;
} else {
var build = false;
}
}
function doTryCatch() {
try {
var build = 1;
} catch (e) {
var f = build;
}
}
Examples of correct code for this rule:
/*eslint block-scoped-var: "error"*/
function doIf() {
var build;
if (true) {
build = true;
}
console.log(build);
}
function doIfElse() {
var build;
if (true) {
build = true;
} else {
build = false;
}
}
function doTryCatch() {
var build;
var f;
try {
build = 1;
} catch (e) {
f = build;
}
}
Further Reading
'miqTreeScrollToNode' is not defined. Open
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
Expected a default case. Open
switch (action) {
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Require Default Case in Switch Statements (default-case)
Some code conventions require that all switch
statements have a default
case, even if the default case is empty, such as:
switch (foo) {
case 1:
doSomething();
break;
case 2:
doSomething();
break;
default:
// do nothing
}
The thinking is that it's better to always explicitly state what the default behavior should be so that it's clear whether or not the developer forgot to include the default behavior by mistake.
Other code conventions allow you to skip the default
case so long as there is a comment indicating the omission is intentional, such as:
switch (foo) {
case 1:
doSomething();
break;
case 2:
doSomething();
break;
// no default
}
Once again, the intent here is to show that the developer intended for there to be no default behavior.
Rule Details
This rule aims to require default
case in switch
statements. You may optionally include a // no default
after the last case
if there is no default
case. The comment may be in any desired case, such as // No Default
.
Examples of incorrect code for this rule:
/*eslint default-case: "error"*/
switch (a) {
case 1:
/* code */
break;
}
Examples of correct code for this rule:
/*eslint default-case: "error"*/
switch (a) {
case 1:
/* code */
break;
default:
/* code */
break;
}
switch (a) {
case 1:
/* code */
break;
// no default
}
switch (a) {
case 1:
/* code */
break;
// No Default
}
Options
This rule accepts a single options argument:
- Set the
commentPattern
option to a regular expression string to change the default/^no default$/i
comment test pattern
commentPattern
Examples of correct code for the { "commentPattern": "^skip\\sdefault" }
option:
/*eslint default-case: ["error", { "commentPattern": "^skip\\sdefault" }]*/
switch(a) {
case 1:
/* code */
break;
// skip default
}
switch(a) {
case 1:
/* code */
break;
// skip default case
}
When Not To Use It
If you don't want to enforce a default
case for switch
statements, you can safely disable this rule.
Related Rules
- [no-fallthrough](no-fallthrough.md) Source: http://eslint.org/docs/rules/
'i' used outside of binding context. Open
to_remove.push(sessionStorage.key(i));
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- Create a ticketCreate a ticket
- Exclude checks
Treat var as Block Scoped (block-scoped-var)
The block-scoped-var
rule generates warnings when variables are used outside of the block in which they were defined. This emulates C-style block scope.
Rule Details
This rule aims to reduce the usage of variables outside of their binding context and emulate traditional block scope from other languages. This is to help newcomers to the language avoid difficult bugs with variable hoisting.
Examples of incorrect code for this rule:
/*eslint block-scoped-var: "error"*/
function doIf() {
if (true) {
var build = true;
}
console.log(build);
}
function doIfElse() {
if (true) {
var build = true;
} else {
var build = false;
}
}
function doTryCatch() {
try {
var build = 1;
} catch (e) {
var f = build;
}
}
Examples of correct code for this rule:
/*eslint block-scoped-var: "error"*/
function doIf() {
var build;
if (true) {
build = true;
}
console.log(build);
}
function doIfElse() {
var build;
if (true) {
build = true;
} else {
build = false;
}
}
function doTryCatch() {
var build;
var f;
try {
build = 1;
} catch (e) {
f = build;
}
}
Further Reading
'miqTreeFindNodeByKey' is not defined. Open
var node = miqTreeFindNodeByKey(tree, key);
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqTreeFindNodeByKey' is not defined. Open
var node = miqTreeFindNodeByKey(tree, key);
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqTreeFindNodeByKey' is not defined. Open
miqTreeObject(tree).options.onNodeSelected(0, miqTreeFindNodeByKey(tree, key));
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'isReduxTree' is not defined. Open
if (isReduxTree(treename)) {
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
Unary operator '++' used. Open
for (var i = 0; i < sessionStorage.length; i++) {
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
disallow the unary operators ++
and --
(no-plusplus)
Because the unary ++
and --
operators are subject to automatic semicolon insertion, differences in whitespace can change semantics of source code.
var i = 10;
var j = 20;
i ++
j
// i = 11, j = 20
var i = 10;
var j = 20;
i
++
j
// i = 10, j = 21
Rule Details
This rule disallows the unary operators ++
and --
.
Examples of incorrect code for this rule:
/*eslint no-plusplus: "error"*/
var foo = 0;
foo++;
var bar = 42;
bar--;
for (i = 0; i < l; i++) {
return;
}
Examples of correct code for this rule:
/*eslint no-plusplus: "error"*/
var foo = 0;
foo += 1;
var bar = 42;
bar -= 1;
for (i = 0; i < l; i += 1) {
return;
}
Options
This rule has an object option.
-
"allowForLoopAfterthoughts": true
allows unary operators++
and--
in the afterthought (final expression) of afor
loop.
allowForLoopAfterthoughts
Examples of correct code for this rule with the { "allowForLoopAfterthoughts": true }
option:
/*eslint no-plusplus: ["error", { "allowForLoopAfterthoughts": true }]*/
for (i = 0; i < l; i++) {
return;
}
for (i = 0; i < l; i--) {
return;
}
Source: http://eslint.org/docs/rules/
'i' used outside of binding context. Open
if (sessionStorage.key(i).match('^tree_state_')) {
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Treat var as Block Scoped (block-scoped-var)
The block-scoped-var
rule generates warnings when variables are used outside of the block in which they were defined. This emulates C-style block scope.
Rule Details
This rule aims to reduce the usage of variables outside of their binding context and emulate traditional block scope from other languages. This is to help newcomers to the language avoid difficult bugs with variable hoisting.
Examples of incorrect code for this rule:
/*eslint block-scoped-var: "error"*/
function doIf() {
if (true) {
var build = true;
}
console.log(build);
}
function doIfElse() {
if (true) {
var build = true;
} else {
var build = false;
}
}
function doTryCatch() {
try {
var build = 1;
} catch (e) {
var f = build;
}
}
Examples of correct code for this rule:
/*eslint block-scoped-var: "error"*/
function doIf() {
var build;
if (true) {
build = true;
}
console.log(build);
}
function doIfElse() {
var build;
if (true) {
build = true;
} else {
build = false;
}
}
function doTryCatch() {
var build;
var f;
try {
build = 1;
} catch (e) {
f = build;
}
}
Further Reading
'miqTreeObject' is not defined. Open
miqTreeObject(treename).removeNode(child);
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqTreeFindNodeByKey' is not defined. Open
var node = miqTreeFindNodeByKey(tree, id);
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqTreeObject' is not defined. Open
var tree = miqTreeObject(tree);
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqTreeFindNodeByKey' is not defined. Open
var node = miqTreeFindNodeByKey(treename, key);
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'i' used outside of binding context. Open
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Treat var as Block Scoped (block-scoped-var)
The block-scoped-var
rule generates warnings when variables are used outside of the block in which they were defined. This emulates C-style block scope.
Rule Details
This rule aims to reduce the usage of variables outside of their binding context and emulate traditional block scope from other languages. This is to help newcomers to the language avoid difficult bugs with variable hoisting.
Examples of incorrect code for this rule:
/*eslint block-scoped-var: "error"*/
function doIf() {
if (true) {
var build = true;
}
console.log(build);
}
function doIfElse() {
if (true) {
var build = true;
} else {
var build = false;
}
}
function doTryCatch() {
try {
var build = 1;
} catch (e) {
var f = build;
}
}
Examples of correct code for this rule:
/*eslint block-scoped-var: "error"*/
function doIf() {
var build;
if (true) {
build = true;
}
console.log(build);
}
function doIfElse() {
var build;
if (true) {
build = true;
} else {
build = false;
}
}
function doTryCatch() {
var build;
var f;
try {
build = 1;
} catch (e) {
f = build;
}
}
Further Reading
Function expected no return value. Open
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require return
statements to either always or never specify values (consistent-return)
Unlike statically-typed languages which enforce that a function returns a specified type of value, JavaScript allows different code paths in a function to return different types of values.
A confusing aspect of JavaScript is that a function returns undefined
if any of the following are true:
- it does not execute a
return
statement before it exits - it executes
return
which does not specify a value explicitly - it executes
return undefined
- it executes
return void
followed by an expression (for example, a function call) - it executes
return
followed by any other expression which evaluates toundefined
If any code paths in a function return a value explicitly but some code path do not return a value explicitly, it might be a typing mistake, especially in a large function. In the following example:
- a code path through the function returns a Boolean value
true
- another code path does not return a value explicitly, therefore returns
undefined
implicitly
function doSomething(condition) {
if (condition) {
return true;
} else {
return;
}
}
Rule Details
This rule requires return
statements to either always or never specify values. This rule ignores function definitions where the name begins with an uppercase letter, because constructors (when invoked with the new
operator) return the instantiated object implicitly if they do not return another object explicitly.
Examples of incorrect code for this rule:
/*eslint consistent-return: "error"*/
function doSomething(condition) {
if (condition) {
return true;
} else {
return;
}
}
function doSomething(condition) {
if (condition) {
return true;
}
}
Examples of correct code for this rule:
/*eslint consistent-return: "error"*/
function doSomething(condition) {
if (condition) {
return true;
} else {
return false;
}
}
function Foo() {
if (!(this instanceof Foo)) {
return new Foo();
}
this.a = 0;
}
Options
This rule has an object option:
-
"treatUndefinedAsUnspecified": false
(default) always either specify values or returnundefined
implicitly only. -
"treatUndefinedAsUnspecified": true
always either specify values or returnundefined
explicitly or implicitly.
treatUndefinedAsUnspecified
Examples of incorrect code for this rule with the default { "treatUndefinedAsUnspecified": false }
option:
/*eslint consistent-return: ["error", { "treatUndefinedAsUnspecified": false }]*/
function foo(callback) {
if (callback) {
return void callback();
}
// no return statement
}
function bar(condition) {
if (condition) {
return undefined;
}
// no return statement
}
Examples of incorrect code for this rule with the { "treatUndefinedAsUnspecified": true }
option:
/*eslint consistent-return: ["error", { "treatUndefinedAsUnspecified": true }]*/
function foo(callback) {
if (callback) {
return void callback();
}
return true;
}
function bar(condition) {
if (condition) {
return undefined;
}
return true;
}
Examples of correct code for this rule with the { "treatUndefinedAsUnspecified": true }
option:
/*eslint consistent-return: ["error", { "treatUndefinedAsUnspecified": true }]*/
function foo(callback) {
if (callback) {
return void callback();
}
// no return statement
}
function bar(condition) {
if (condition) {
return undefined;
}
// no return statement
}
When Not To Use It
If you want to allow functions to have different return
behavior depending on code branching, then it is safe to disable this rule.
Source: http://eslint.org/docs/rules/
'miqTreeObject' is not defined. Open
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqTreeScrollToNode' is not defined. Open
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqTreeClearState' is not defined. Open
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'isReduxTree' is not defined. Open
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqMenuChangeRow' is not defined. Open
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
for..in loops iterate over the entire prototype chain, which is virtually never what you want. Use Object.{keys,values,entries}, and iterate over the resulting array. Open
for (var property in tree) {
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disallow specified syntax (no-restricted-syntax)
JavaScript has a lot of language features, and not everyone likes all of them. As a result, some projects choose to disallow the use of certain language features altogether. For instance, you might decide to disallow the use of try-catch
or class
, or you might decide to disallow the use of the in
operator.
Rather than creating separate rules for every language feature you want to turn off, this rule allows you to configure the syntax elements you want to restrict use of. These elements are represented by their ESTree node types. For example, a function declaration is represented by FunctionDeclaration
and the with
statement is represented by WithStatement
. You may find the full list of AST node names you can use on GitHub and use the online parser to see what type of nodes your code consists of.
You can also specify [AST selectors](../developer-guide/selectors) to restrict, allowing much more precise control over syntax patterns.
Rule Details
This rule disallows specified (that is, user-defined) syntax.
Options
This rule takes a list of strings, where each string is an AST selector:
{
"rules": {
"no-restricted-syntax": ["error", "FunctionExpression", "WithStatement", "BinaryExpression[operator='in']"]
}
}
Alternatively, the rule also accepts objects, where the selector and an optional custom message are specified:
{
"rules": {
"no-restricted-syntax": [
"error",
{
"selector": "FunctionExpression",
"message": "Function expressions are not allowed."
},
{
"selector": "CallExpression[callee.name='setTimeout'][arguments.length!=2]",
"message": "setTimeout must always be invoked with two arguments."
}
]
}
}
If a custom message is specified with the message
property, ESLint will use that message when reporting occurrences of the syntax specified in the selector
property.
The string and object formats can be freely mixed in the configuration as needed.
Examples of incorrect code for this rule with the "FunctionExpression", "WithStatement", BinaryExpression[operator='in']
options:
/* eslint no-restricted-syntax: ["error", "FunctionExpression", "WithStatement", "BinaryExpression[operator='in']"] */
with (me) {
dontMess();
}
var doSomething = function () {};
foo in bar;
Examples of correct code for this rule with the "FunctionExpression", "WithStatement", BinaryExpression[operator='in']
options:
/* eslint no-restricted-syntax: ["error", "FunctionExpression", "WithStatement", "BinaryExpression[operator='in']"] */
me.dontMess();
function doSomething() {};
foo instanceof bar;
When Not To Use It
If you don't want to restrict your code from using any JavaScript features or syntax, you should not use this rule.
Related Rules
- [no-alert](no-alert.md)
- [no-console](no-console.md)
- [no-debugger](no-debugger.md)
- [no-restricted-properties](no-restricted-properties.md) Source: http://eslint.org/docs/rules/
'i' used outside of binding context. Open
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Treat var as Block Scoped (block-scoped-var)
The block-scoped-var
rule generates warnings when variables are used outside of the block in which they were defined. This emulates C-style block scope.
Rule Details
This rule aims to reduce the usage of variables outside of their binding context and emulate traditional block scope from other languages. This is to help newcomers to the language avoid difficult bugs with variable hoisting.
Examples of incorrect code for this rule:
/*eslint block-scoped-var: "error"*/
function doIf() {
if (true) {
var build = true;
}
console.log(build);
}
function doIfElse() {
if (true) {
var build = true;
} else {
var build = false;
}
}
function doTryCatch() {
try {
var build = 1;
} catch (e) {
var f = build;
}
}
Examples of correct code for this rule:
/*eslint block-scoped-var: "error"*/
function doIf() {
var build;
if (true) {
build = true;
}
console.log(build);
}
function doIfElse() {
var build;
if (true) {
build = true;
} else {
build = false;
}
}
function doTryCatch() {
var build;
var f;
try {
build = 1;
} catch (e) {
f = build;
}
}
Further Reading
'i' used outside of binding context. Open
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Treat var as Block Scoped (block-scoped-var)
The block-scoped-var
rule generates warnings when variables are used outside of the block in which they were defined. This emulates C-style block scope.
Rule Details
This rule aims to reduce the usage of variables outside of their binding context and emulate traditional block scope from other languages. This is to help newcomers to the language avoid difficult bugs with variable hoisting.
Examples of incorrect code for this rule:
/*eslint block-scoped-var: "error"*/
function doIf() {
if (true) {
var build = true;
}
console.log(build);
}
function doIfElse() {
if (true) {
var build = true;
} else {
var build = false;
}
}
function doTryCatch() {
try {
var build = 1;
} catch (e) {
var f = build;
}
}
Examples of correct code for this rule:
/*eslint block-scoped-var: "error"*/
function doIf() {
var build;
if (true) {
build = true;
}
console.log(build);
}
function doIfElse() {
var build;
if (true) {
build = true;
} else {
build = false;
}
}
function doTryCatch() {
var build;
var f;
try {
build = 1;
} catch (e) {
f = build;
}
}
Further Reading
'i' used outside of binding context. Open
sessionStorage.removeItem(to_remove[i]);
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- Exclude checks
Treat var as Block Scoped (block-scoped-var)
The block-scoped-var
rule generates warnings when variables are used outside of the block in which they were defined. This emulates C-style block scope.
Rule Details
This rule aims to reduce the usage of variables outside of their binding context and emulate traditional block scope from other languages. This is to help newcomers to the language avoid difficult bugs with variable hoisting.
Examples of incorrect code for this rule:
/*eslint block-scoped-var: "error"*/
function doIf() {
if (true) {
var build = true;
}
console.log(build);
}
function doIfElse() {
if (true) {
var build = true;
} else {
var build = false;
}
}
function doTryCatch() {
try {
var build = 1;
} catch (e) {
var f = build;
}
}
Examples of correct code for this rule:
/*eslint block-scoped-var: "error"*/
function doIf() {
var build;
if (true) {
build = true;
}
console.log(build);
}
function doIfElse() {
var build;
if (true) {
build = true;
} else {
build = false;
}
}
function doTryCatch() {
var build;
var f;
try {
build = 1;
} catch (e) {
f = build;
}
}
Further Reading
'miqTreeObject' is not defined. Open
miqTreeObject(treename).expandNode(node);
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqTreeActivateNodeSilently' is not defined. Open
miqTreeActivateNodeSilently(treename, selected_node);
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqTreeClearState' is not defined. Open
miqTreeClearState(treename);
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqTreeObject' is not defined. Open
miqTreeObject(treename).addNode(children, node);
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqGetSelectedKeys' is not defined. Open
var selectedKeys = miqGetSelectedKeys(tree);
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'isReduxTree' is not defined. Open
if (isReduxTree(treename)) {
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqMenuChangeRow' is not defined. Open
miqMenuChangeRow('activate', elem);
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqTreeToggleExpand' is not defined. Open
miqTreeToggleExpand(treeName, false);
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqTreeFindNodeByKey' is not defined. Open
var node = miqTreeFindNodeByKey(treename, key);
- Read upRead up
- Create a ticketCreate a ticket
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqTreeObject' is not defined. Open
miqTreeObject(treename).revealNode(node, {silent: true});
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqTreeExpandNode' is not defined. Open
miqTreeExpandNode(treeId, currId);
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'i' is already defined. Open
for (var i = 0; i < to_remove.length; i++) {
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disallow variable redeclaration (no-redeclare)
In JavaScript, it's possible to redeclare the same variable name using var
. This can lead to confusion as to where the variable is actually declared and initialized.
Rule Details
This rule is aimed at eliminating variables that have multiple declarations in the same scope.
Examples of incorrect code for this rule:
/*eslint no-redeclare: "error"*/
var a = 3;
var a = 10;
Examples of correct code for this rule:
/*eslint no-redeclare: "error"*/
var a = 3;
// ...
a = 10;
Options
This rule takes one optional argument, an object with a boolean property "builtinGlobals"
. It defaults to false
.
If set to true
, this rule also checks redeclaration of built-in globals, such as Object
, Array
, Number
...
builtinGlobals
The "builtinGlobals"
option will check for redeclaration of built-in globals in global scope.
Examples of incorrect code for the { "builtinGlobals": true }
option:
/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
var Object = 0;
Examples of incorrect code for the { "builtinGlobals": true }
option and the browser
environment:
/*eslint no-redeclare: ["error", { "builtinGlobals": true }]*/
/*eslint-env browser*/
var top = 0;
The browser
environment has many built-in global variables (for example, top
). Some of built-in global variables cannot be redeclared.
Note that when using the node
or commonjs
environments (or ecmaFeatures.globalReturn
, if using the default parser), the top scope of a program is not actually the global scope, but rather a "module" scope. When this is the case, declaring a variable named after a builtin global is not a redeclaration, but rather a shadowing of the global variable. In that case, the [no-shadow
](no-shadow.md) rule with the "builtinGlobals"
option should be used.
Related Rules
- [no-shadow](no-shadow.md) Source: http://eslint.org/docs/rules/
'isReduxTree' is not defined. Open
if (isReduxTree(tree)) {
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqTreeObject' is not defined. Open
expand_mode ? miqTreeObject(treename).expandAll() : miqTreeObject(treename).collapseAll();
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- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'miqMenuChangeRow' is not defined. Open
return miqMenuChangeRow('activate', this);
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Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment, or specified in the globals
key in the configuration file. A common use case for these is if you intentionally use globals that are defined elsewhere (e.g. in a script sourced from HTML).
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in [Specifying Environments](../user-guide/configuring.md#specifying-environments). A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
Node.js
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'i' used outside of binding context. Open
for (var i = 0; i < sessionStorage.length; i++) {
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Treat var as Block Scoped (block-scoped-var)
The block-scoped-var
rule generates warnings when variables are used outside of the block in which they were defined. This emulates C-style block scope.
Rule Details
This rule aims to reduce the usage of variables outside of their binding context and emulate traditional block scope from other languages. This is to help newcomers to the language avoid difficult bugs with variable hoisting.
Examples of incorrect code for this rule:
/*eslint block-scoped-var: "error"*/
function doIf() {
if (true) {
var build = true;
}
console.log(build);
}
function doIfElse() {
if (true) {
var build = true;
} else {
var build = false;
}
}
function doTryCatch() {
try {
var build = 1;
} catch (e) {
var f = build;
}
}
Examples of correct code for this rule:
/*eslint block-scoped-var: "error"*/
function doIf() {
var build;
if (true) {
build = true;
}
console.log(build);
}
function doIfElse() {
var build;
if (true) {
build = true;
} else {
build = false;
}
}
function doTryCatch() {
var build;
var f;
try {
build = 1;
} catch (e) {
f = build;
}
}
Further Reading
'i' used outside of binding context. Open
for (var i = 0; i < to_remove.length; i++) {
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Treat var as Block Scoped (block-scoped-var)
The block-scoped-var
rule generates warnings when variables are used outside of the block in which they were defined. This emulates C-style block scope.
Rule Details
This rule aims to reduce the usage of variables outside of their binding context and emulate traditional block scope from other languages. This is to help newcomers to the language avoid difficult bugs with variable hoisting.
Examples of incorrect code for this rule:
/*eslint block-scoped-var: "error"*/
function doIf() {
if (true) {
var build = true;
}
console.log(build);
}
function doIfElse() {
if (true) {
var build = true;
} else {
var build = false;
}
}
function doTryCatch() {
try {
var build = 1;
} catch (e) {
var f = build;
}
}
Examples of correct code for this rule:
/*eslint block-scoped-var: "error"*/
function doIf() {
var build;
if (true) {
build = true;
}
console.log(build);
}
function doIfElse() {
var build;
if (true) {
build = true;
} else {
build = false;
}
}
function doTryCatch() {
var build;
var f;
try {
build = 1;
} catch (e) {
f = build;
}
}
Further Reading
Do not access Object.prototype method 'hasOwnProperty' from target object. Open
return store.hasOwnProperty(treeName);
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Disallow use of Object.prototypes builtins directly (no-prototype-builtins)
In ECMAScript 5.1, Object.create
was added, which enables the creation of objects with a specified [[Prototype]]
. Object.create(null)
is a common pattern used to create objects that will be used as a Map. This can lead to errors when it is assumed that objects will have properties from Object.prototype
. This rule prevents calling some Object.prototype
methods directly from an object.
Additionally, objects can have properties that shadow the builtins on Object.prototype
, potentially causing unintended behavior or denial-of-service security vulnerabilities. For example, it would be unsafe for a webserver to parse JSON input from a client and call hasOwnProperty
directly on the resulting object, because a malicious client could send a JSON value like {"hasOwnProperty": 1}
and cause the server to crash.
To avoid subtle bugs like this, it's better to always call these methods from Object.prototype
. For example, foo.hasOwnProperty("bar")
should be replaced with Object.prototype.hasOwnProperty.call(foo, "bar")
.
Rule Details
This rule disallows calling some Object.prototype
methods directly on object instances.
Examples of incorrect code for this rule:
/*eslint no-prototype-builtins: "error"*/
var hasBarProperty = foo.hasOwnProperty("bar");
var isPrototypeOfBar = foo.isPrototypeOf(bar);
var barIsEnumerable = foo.propertyIsEnumerable("bar");
Examples of correct code for this rule:
/*eslint no-prototype-builtins: "error"*/
var hasBarProperty = Object.prototype.hasOwnProperty.call(foo, "bar");
var isPrototypeOfBar = Object.prototype.isPrototypeOf.call(foo, bar);
var barIsEnumerable = {}.propertyIsEnumerable.call(foo, "bar");
When Not To Use It
You may want to turn this rule off if your code only touches objects with hardcoded keys, and you will never use an object that shadows an Object.prototype
method or which does not inherit from Object.prototype
.
Source: http://eslint.org/docs/rules/
Do not access Object.prototype method 'hasOwnProperty' from target object. Open
if (tree.hasOwnProperty(property) && property !== '') {
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Disallow use of Object.prototypes builtins directly (no-prototype-builtins)
In ECMAScript 5.1, Object.create
was added, which enables the creation of objects with a specified [[Prototype]]
. Object.create(null)
is a common pattern used to create objects that will be used as a Map. This can lead to errors when it is assumed that objects will have properties from Object.prototype
. This rule prevents calling some Object.prototype
methods directly from an object.
Additionally, objects can have properties that shadow the builtins on Object.prototype
, potentially causing unintended behavior or denial-of-service security vulnerabilities. For example, it would be unsafe for a webserver to parse JSON input from a client and call hasOwnProperty
directly on the resulting object, because a malicious client could send a JSON value like {"hasOwnProperty": 1}
and cause the server to crash.
To avoid subtle bugs like this, it's better to always call these methods from Object.prototype
. For example, foo.hasOwnProperty("bar")
should be replaced with Object.prototype.hasOwnProperty.call(foo, "bar")
.
Rule Details
This rule disallows calling some Object.prototype
methods directly on object instances.
Examples of incorrect code for this rule:
/*eslint no-prototype-builtins: "error"*/
var hasBarProperty = foo.hasOwnProperty("bar");
var isPrototypeOfBar = foo.isPrototypeOf(bar);
var barIsEnumerable = foo.propertyIsEnumerable("bar");
Examples of correct code for this rule:
/*eslint no-prototype-builtins: "error"*/
var hasBarProperty = Object.prototype.hasOwnProperty.call(foo, "bar");
var isPrototypeOfBar = Object.prototype.isPrototypeOf.call(foo, bar);
var barIsEnumerable = {}.propertyIsEnumerable.call(foo, "bar");
When Not To Use It
You may want to turn this rule off if your code only touches objects with hardcoded keys, and you will never use an object that shadows an Object.prototype
method or which does not inherit from Object.prototype
.
Source: http://eslint.org/docs/rules/
Similar blocks of code found in 2 locations. Consider refactoring. Open
if (isReduxTree(tree)) {
ManageIQ.redux.store.dispatch({namespace: tree, type: '@@tree/selectNode', key: key});
ManageIQ.redux.store.dispatch({namespace: tree, type: '@@tree/expandNode', key: key});
ManageIQ.redux.store.dispatch({namespace: tree, type: '@@tree/scrollToNode', key: key});
} else {
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Duplicated Code
Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:
Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.
When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).
Tuning
This issue has a mass of 109.
We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.
The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.
If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.
See codeclimate-duplication
's documentation for more information about tuning the mass threshold in your .codeclimate.yml
.
Refactorings
- Extract Method
- Extract Class
- Form Template Method
- Introduce Null Object
- Pull Up Method
- Pull Up Field
- Substitute Algorithm
Further Reading
- Don't Repeat Yourself on the C2 Wiki
- Duplicated Code on SourceMaking
- Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76
Similar blocks of code found in 2 locations. Consider refactoring. Open
if (isReduxTree(tree)) {
ManageIQ.redux.store.dispatch({namespace: tree, type: '@@tree/selectNodeSilent', key: key});
ManageIQ.redux.store.dispatch({namespace: tree, type: '@@tree/expandNode', key: key});
ManageIQ.redux.store.dispatch({namespace: tree, type: '@@tree/scrollToNode', key: key});
} else {
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Duplicated Code
Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:
Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.
When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).
Tuning
This issue has a mass of 109.
We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.
The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.
If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.
See codeclimate-duplication
's documentation for more information about tuning the mass threshold in your .codeclimate.yml
.
Refactorings
- Extract Method
- Extract Class
- Form Template Method
- Introduce Null Object
- Pull Up Method
- Pull Up Field
- Substitute Algorithm
Further Reading
- Don't Repeat Yourself on the C2 Wiki
- Duplicated Code on SourceMaking
- Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76
Similar blocks of code found in 2 locations. Consider refactoring. Open
} else {
$('#squash_button i').attr('class', 'fa fa-plus-square-o fa-lg');
$('#squash_button').prop('title', __('Expand All'));
miqTreeToggleExpand(treeName, false);
ManageIQ.tree.expandAll = true;
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Duplicated Code
Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:
Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.
When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).
Tuning
This issue has a mass of 62.
We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.
The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.
If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.
See codeclimate-duplication
's documentation for more information about tuning the mass threshold in your .codeclimate.yml
.
Refactorings
- Extract Method
- Extract Class
- Form Template Method
- Introduce Null Object
- Pull Up Method
- Pull Up Field
- Substitute Algorithm
Further Reading
- Don't Repeat Yourself on the C2 Wiki
- Duplicated Code on SourceMaking
- Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76
Similar blocks of code found in 2 locations. Consider refactoring. Open
if (ManageIQ.tree.expandAll) {
$('#squash_button i').attr('class', 'fa fa-minus-square-o fa-lg');
$('#squash_button').prop('title', __('Collapse All'));
miqTreeToggleExpand(treeName, true);
ManageIQ.tree.expandAll = false;
- Read upRead up
- Create a ticketCreate a ticket
Duplicated Code
Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:
Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.
When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).
Tuning
This issue has a mass of 62.
We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.
The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.
If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.
See codeclimate-duplication
's documentation for more information about tuning the mass threshold in your .codeclimate.yml
.
Refactorings
- Extract Method
- Extract Class
- Form Template Method
- Introduce Null Object
- Pull Up Method
- Pull Up Field
- Substitute Algorithm
Further Reading
- Don't Repeat Yourself on the C2 Wiki
- Duplicated Code on SourceMaking
- Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76
Similar blocks of code found in 2 locations. Consider refactoring. Open
window.miqOnClickAutomate = function(id) {
miqJqueryRequest('/' + ManageIQ.controller + '/ae_tree_select/?id=' + encodeURIComponent(id) + '&tree=automate_tree');
}
- Read upRead up
- Create a ticketCreate a ticket
Duplicated Code
Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:
Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.
When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).
Tuning
This issue has a mass of 47.
We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.
The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.
If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.
See codeclimate-duplication
's documentation for more information about tuning the mass threshold in your .codeclimate.yml
.
Refactorings
- Extract Method
- Extract Class
- Form Template Method
- Introduce Null Object
- Pull Up Method
- Pull Up Field
- Substitute Algorithm
Further Reading
- Don't Repeat Yourself on the C2 Wiki
- Duplicated Code on SourceMaking
- Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76
Similar blocks of code found in 2 locations. Consider refactoring. Open
window.miqOnClickAutomateCatalog = function(id) {
miqJqueryRequest('/' + ManageIQ.controller + '/ae_tree_select/?id=' + encodeURIComponent(id) + '&tree=automate_catalog_tree');
}
- Read upRead up
- Create a ticketCreate a ticket
Duplicated Code
Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:
Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.
When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).
Tuning
This issue has a mass of 47.
We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.
The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.
If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.
See codeclimate-duplication
's documentation for more information about tuning the mass threshold in your .codeclimate.yml
.
Refactorings
- Extract Method
- Extract Class
- Form Template Method
- Introduce Null Object
- Pull Up Method
- Pull Up Field
- Substitute Algorithm
Further Reading
- Don't Repeat Yourself on the C2 Wiki
- Duplicated Code on SourceMaking
- Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76