id, name, last_run_on, count, action, url, queue_url,

Close

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/

  id, report_id, name, last_run_on, userid, url,

Close

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/

  id, report_id, name, last_run_on, userid, url,

Close

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/

    $onClick: (e) => click(url, e),

Close

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/

  id, name, last_run_on, count, action, url, queue_url,

Close

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/

export function miqOptimizationTransform(row) {

Close

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 to undefined

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 return undefined implicitly only.
• "treatUndefinedAsUnspecified": true always either specify values or return undefined 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/

  switch (row.klass) {

Close

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/

  id, report_id, name, last_run_on, userid, url,

Close

Disallow Unused Variables (no-unused-vars)

Variables that are declared and not used anywhere in the code are most likely an error due to incomplete refactoring. Such variables take up space in the code and can lead to confusion by readers.

Rule Details

This rule is aimed at eliminating unused variables, functions, and function parameters.

A variable foo is considered to be used if any of the following are true:

• It is called (foo()) or constructed (new foo())
• It is read (var bar = foo)
• It is passed into a function as an argument (doSomething(foo))
• It is read inside of a function that is passed to another function (doSomething(function() { foo(); }))

A variable is not considered to be used if it is only ever declared (var foo = 5) or assigned to (foo = 7).

Examples of incorrect code for this rule:

/*eslint no-unused-vars: "error"*/
/*global some_unused_var*/

// It checks variables you have defined as global
some_unused_var = 42;

var x;

// Write-only variables are not considered as used.
var y = 10;
y = 5;

// A read for a modification of itself is not considered as used.
var z = 0;
z = z + 1;

// By default, unused arguments cause warnings.
(function(foo) {
    return 5;
})();

// Unused recursive functions also cause warnings.
function fact(n) {
    if (n < 2) return 1;
    return n * fact(n - 1);
}

// When a function definition destructures an array, unused entries from the array also cause warnings.
function getY([x, y]) {
    return y;
}

Examples of correct code for this rule:

/*eslint no-unused-vars: "error"*/

var x = 10;
alert(x);

// foo is considered used here
myFunc(function foo() {
    // ...
}.bind(this));

(function(foo) {
    return foo;
})();

var myFunc;
myFunc = setTimeout(function() {
    // myFunc is considered used
    myFunc();
}, 50);

// Only the second argument from the descructured array is used.
function getY([, y]) {
    return y;
}

exported

In environments outside of CommonJS or ECMAScript modules, you may use var to create a global variable that may be used by other scripts. You can use the /* exported variableName */ comment block to indicate that this variable is being exported and therefore should not be considered unused.

Note that /* exported */ has no effect for any of the following:

• when the environment is node or commonjs
• when parserOptions.sourceType is module
• when ecmaFeatures.globalReturn is true

The line comment // exported variableName will not work as exported is not line-specific.

Examples of correct code for /* exported variableName */ operation:

/* exported global_var */

var global_var = 42;

Options

This rule takes one argument which can be a string or an object. The string settings are the same as those of the vars property (explained below).

By default this rule is enabled with all option for variables and after-used for arguments.

{
    "rules": {
        "no-unused-vars": ["error", { "vars": "all", "args": "after-used", "ignoreRestSiblings": false }]
    }
}

vars

The vars option has two settings:

• all checks all variables for usage, including those in the global scope. This is the default setting.
• local checks only that locally-declared variables are used but will allow global variables to be unused.

vars: local

Examples of correct code for the { "vars": "local" } option:

/*eslint no-unused-vars: ["error", { "vars": "local" }]*/
/*global some_unused_var */

some_unused_var = 42;

varsIgnorePattern

The varsIgnorePattern option specifies exceptions not to check for usage: variables whose names match a regexp pattern. For example, variables whose names contain ignored or Ignored.

Examples of correct code for the { "varsIgnorePattern": "[iI]gnored" } option:

/*eslint no-unused-vars: ["error", { "varsIgnorePattern": "[iI]gnored" }]*/

var firstVarIgnored = 1;
var secondVar = 2;
console.log(secondVar);

args

The args option has three settings:

• after-used - unused positional arguments that occur before the last used argument will not be checked, but all named arguments and all positional arguments after the last used argument will be checked.
• all - all named arguments must be used.
• none - do not check arguments.

args: after-used

Examples of incorrect code for the default { "args": "after-used" } option:

/*eslint no-unused-vars: ["error", { "args": "after-used" }]*/

// 2 errors, for the parameters after the last used parameter (bar)
// "baz" is defined but never used
// "qux" is defined but never used
(function(foo, bar, baz, qux) {
    return bar;
})();

Examples of correct code for the default { "args": "after-used" } option:

/*eslint no-unused-vars: ["error", {"args": "after-used"}]*/

(function(foo, bar, baz, qux) {
    return qux;
})();

args: all

Examples of incorrect code for the { "args": "all" } option:

/*eslint no-unused-vars: ["error", { "args": "all" }]*/

// 2 errors
// "foo" is defined but never used
// "baz" is defined but never used
(function(foo, bar, baz) {
    return bar;
})();

args: none

Examples of correct code for the { "args": "none" } option:

/*eslint no-unused-vars: ["error", { "args": "none" }]*/

(function(foo, bar, baz) {
    return bar;
})();

ignoreRestSiblings

The ignoreRestSiblings option is a boolean (default: false). Using a Rest Property it is possible to "omit" properties from an object, but by default the sibling properties are marked as "unused". With this option enabled the rest property's siblings are ignored.

Examples of correct code for the { "ignoreRestSiblings": true } option:

/*eslint no-unused-vars: ["error", { "ignoreRestSiblings": true }]*/
// 'type' is ignored because it has a rest property sibling.
var { type, ...coords } = data;

argsIgnorePattern

The argsIgnorePattern option specifies exceptions not to check for usage: arguments whose names match a regexp pattern. For example, variables whose names begin with an underscore.

Examples of correct code for the { "argsIgnorePattern": "^_" } option:

/*eslint no-unused-vars: ["error", { "argsIgnorePattern": "^_" }]*/

function foo(x, _y) {
    return x + 1;
}
foo();

caughtErrors

The caughtErrors option is used for catch block arguments validation.

It has two settings:

• none - do not check error objects. This is the default setting.
• all - all named arguments must be used.

caughtErrors: none

Not specifying this rule is equivalent of assigning it to none.

Examples of correct code for the { "caughtErrors": "none" } option:

/*eslint no-unused-vars: ["error", { "caughtErrors": "none" }]*/

try {
    //...
} catch (err) {
    console.error("errors");
}

caughtErrors: all

Examples of incorrect code for the { "caughtErrors": "all" } option:

/*eslint no-unused-vars: ["error", { "caughtErrors": "all" }]*/

// 1 error
// "err" is defined but never used
try {
    //...
} catch (err) {
    console.error("errors");
}

caughtErrorsIgnorePattern

The caughtErrorsIgnorePattern option specifies exceptions not to check for usage: catch arguments whose names match a regexp pattern. For example, variables whose names begin with a string 'ignore'.

Examples of correct code for the { "caughtErrorsIgnorePattern": "^ignore" } option:

/*eslint no-unused-vars: ["error", { "caughtErrorsIgnorePattern": "^ignore" }]*/

try {
    //...
} catch (ignoreErr) {
    console.error("errors");
}

When Not To Use It

If you don't want to be notified about unused variables or function arguments, you can safely turn this rule off. Source: http://eslint.org/docs/rules/

  id, name, last_run_on, count, action, url, queue_url,

Close

Disallow Unused Variables (no-unused-vars)

Variables that are declared and not used anywhere in the code are most likely an error due to incomplete refactoring. Such variables take up space in the code and can lead to confusion by readers.

Rule Details

This rule is aimed at eliminating unused variables, functions, and function parameters.

A variable foo is considered to be used if any of the following are true:

• It is called (foo()) or constructed (new foo())
• It is read (var bar = foo)
• It is passed into a function as an argument (doSomething(foo))
• It is read inside of a function that is passed to another function (doSomething(function() { foo(); }))

A variable is not considered to be used if it is only ever declared (var foo = 5) or assigned to (foo = 7).

Examples of incorrect code for this rule:

/*eslint no-unused-vars: "error"*/
/*global some_unused_var*/

// It checks variables you have defined as global
some_unused_var = 42;

var x;

// Write-only variables are not considered as used.
var y = 10;
y = 5;

// A read for a modification of itself is not considered as used.
var z = 0;
z = z + 1;

// By default, unused arguments cause warnings.
(function(foo) {
    return 5;
})();

// Unused recursive functions also cause warnings.
function fact(n) {
    if (n < 2) return 1;
    return n * fact(n - 1);
}

// When a function definition destructures an array, unused entries from the array also cause warnings.
function getY([x, y]) {
    return y;
}

Examples of correct code for this rule:

/*eslint no-unused-vars: "error"*/

var x = 10;
alert(x);

// foo is considered used here
myFunc(function foo() {
    // ...
}.bind(this));

(function(foo) {
    return foo;
})();

var myFunc;
myFunc = setTimeout(function() {
    // myFunc is considered used
    myFunc();
}, 50);

// Only the second argument from the descructured array is used.
function getY([, y]) {
    return y;
}

exported

In environments outside of CommonJS or ECMAScript modules, you may use var to create a global variable that may be used by other scripts. You can use the /* exported variableName */ comment block to indicate that this variable is being exported and therefore should not be considered unused.

Note that /* exported */ has no effect for any of the following:

• when the environment is node or commonjs
• when parserOptions.sourceType is module
• when ecmaFeatures.globalReturn is true

The line comment // exported variableName will not work as exported is not line-specific.

Examples of correct code for /* exported variableName */ operation:

/* exported global_var */

var global_var = 42;

Options

This rule takes one argument which can be a string or an object. The string settings are the same as those of the vars property (explained below).

By default this rule is enabled with all option for variables and after-used for arguments.

{
    "rules": {
        "no-unused-vars": ["error", { "vars": "all", "args": "after-used", "ignoreRestSiblings": false }]
    }
}

vars

The vars option has two settings:

• all checks all variables for usage, including those in the global scope. This is the default setting.
• local checks only that locally-declared variables are used but will allow global variables to be unused.

vars: local

Examples of correct code for the { "vars": "local" } option:

/*eslint no-unused-vars: ["error", { "vars": "local" }]*/
/*global some_unused_var */

some_unused_var = 42;

varsIgnorePattern

The varsIgnorePattern option specifies exceptions not to check for usage: variables whose names match a regexp pattern. For example, variables whose names contain ignored or Ignored.

Examples of correct code for the { "varsIgnorePattern": "[iI]gnored" } option:

/*eslint no-unused-vars: ["error", { "varsIgnorePattern": "[iI]gnored" }]*/

var firstVarIgnored = 1;
var secondVar = 2;
console.log(secondVar);

args

The args option has three settings:

• after-used - unused positional arguments that occur before the last used argument will not be checked, but all named arguments and all positional arguments after the last used argument will be checked.
• all - all named arguments must be used.
• none - do not check arguments.

args: after-used

Examples of incorrect code for the default { "args": "after-used" } option:

/*eslint no-unused-vars: ["error", { "args": "after-used" }]*/

// 2 errors, for the parameters after the last used parameter (bar)
// "baz" is defined but never used
// "qux" is defined but never used
(function(foo, bar, baz, qux) {
    return bar;
})();

Examples of correct code for the default { "args": "after-used" } option:

/*eslint no-unused-vars: ["error", {"args": "after-used"}]*/

(function(foo, bar, baz, qux) {
    return qux;
})();

args: all

Examples of incorrect code for the { "args": "all" } option:

/*eslint no-unused-vars: ["error", { "args": "all" }]*/

// 2 errors
// "foo" is defined but never used
// "baz" is defined but never used
(function(foo, bar, baz) {
    return bar;
})();

args: none

Examples of correct code for the { "args": "none" } option:

/*eslint no-unused-vars: ["error", { "args": "none" }]*/

(function(foo, bar, baz) {
    return bar;
})();

ignoreRestSiblings

The ignoreRestSiblings option is a boolean (default: false). Using a Rest Property it is possible to "omit" properties from an object, but by default the sibling properties are marked as "unused". With this option enabled the rest property's siblings are ignored.

Examples of correct code for the { "ignoreRestSiblings": true } option:

/*eslint no-unused-vars: ["error", { "ignoreRestSiblings": true }]*/
// 'type' is ignored because it has a rest property sibling.
var { type, ...coords } = data;

argsIgnorePattern

The argsIgnorePattern option specifies exceptions not to check for usage: arguments whose names match a regexp pattern. For example, variables whose names begin with an underscore.

Examples of correct code for the { "argsIgnorePattern": "^_" } option:

/*eslint no-unused-vars: ["error", { "argsIgnorePattern": "^_" }]*/

function foo(x, _y) {
    return x + 1;
}
foo();

caughtErrors

The caughtErrors option is used for catch block arguments validation.

It has two settings:

• none - do not check error objects. This is the default setting.
• all - all named arguments must be used.

caughtErrors: none

Not specifying this rule is equivalent of assigning it to none.

Examples of correct code for the { "caughtErrors": "none" } option:

/*eslint no-unused-vars: ["error", { "caughtErrors": "none" }]*/

try {
    //...
} catch (err) {
    console.error("errors");
}

caughtErrors: all

Examples of incorrect code for the { "caughtErrors": "all" } option:

/*eslint no-unused-vars: ["error", { "caughtErrors": "all" }]*/

// 1 error
// "err" is defined but never used
try {
    //...
} catch (err) {
    console.error("errors");
}

caughtErrorsIgnorePattern

The caughtErrorsIgnorePattern option specifies exceptions not to check for usage: catch arguments whose names match a regexp pattern. For example, variables whose names begin with a string 'ignore'.

Examples of correct code for the { "caughtErrorsIgnorePattern": "^ignore" } option:

/*eslint no-unused-vars: ["error", { "caughtErrorsIgnorePattern": "^ignore" }]*/

try {
    //...
} catch (ignoreErr) {
    console.error("errors");
}

When Not To Use It

If you don't want to be notified about unused variables or function arguments, you can safely turn this rule off. Source: http://eslint.org/docs/rules/