Showing 51 of 51 total issues
Unexpected mix of '||' and '&&'. Open
assert(t.isIdentifier(key) || t.isLiteral(key) && typeof key.value === 'string', 'key must be a string or identifier');
- Read upRead up
- Exclude checks
Disallow mixes of different operators (no-mixed-operators)
Enclosing complex expressions by parentheses clarifies the developer's intention, which makes the code more readable. This rule warns when different operators are used consecutively without parentheses in an expression.
var foo = a && b || c || d; /*BAD: Unexpected mix of '&&' and '||'.*/
var foo = (a && b) || c || d; /*GOOD*/
var foo = a && (b || c || d); /*GOOD*/
Rule Details
This rule checks BinaryExpression
and LogicalExpression
.
This rule may conflict with [no-extra-parens](no-extra-parens.md) rule.
If you use both this and [no-extra-parens](no-extra-parens.md) rule together, you need to use the nestedBinaryExpressions
option of [no-extra-parens](no-extra-parens.md) rule.
Examples of incorrect code for this rule:
/*eslint no-mixed-operators: "error"*/
var foo = a && b < 0 || c > 0 || d + 1 === 0;
var foo = a + b * c;
Examples of correct code for this rule:
/*eslint no-mixed-operators: "error"*/
var foo = a || b || c;
var foo = a && b && c;
var foo = (a && b < 0) || c > 0 || d + 1 === 0;
var foo = a && (b < 0 || c > 0 || d + 1 === 0);
var foo = a + (b * c);
var foo = (a + b) * c;
Options
{
"no-mixed-operators": [
"error",
{
"groups": [
["+", "-", "*", "/", "%", "**"],
["&", "|", "^", "~", "<<", ">>", ">>>"],
["==", "!=", "===", "!==", ">", ">=", "<", "<="],
["&&", "||"],
["in", "instanceof"]
],
"allowSamePrecedence": true
}
]
}
This rule has 2 options.
-
groups
(string[][]
) - specifies groups to compare operators. When this rule compares two operators, if both operators are included in a same group, this rule checks it. Otherwise, this rule ignores it. This value is a list of groups. The group is a list of binary operators. Default is the groups for each kind of operators. -
allowSamePrecedence
(boolean
) - specifies to allow mix of 2 operators if those have the same precedence. Default istrue
.
groups
The following operators can be used in groups
option:
- Arithmetic Operators:
"+"
,"-"
,"*"
,"/"
,"%"
,"**"
- Bitwise Operators:
"&"
,"|"
,"^"
,"~"
,"<<"
,">>"
,">>>"
- Comparison Operators:
"=="
,"!="
,"==="
,"!=="
,">"
,">="
,"<"
,"<="
- Logical Operators:
"&&"
,"||"
- Relational Operators:
"in"
,"instanceof"
Now, considers about {"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]}
configure.
This configure has 2 groups: bitwise operators and logical operators.
This rule checks only if both operators are included in a same group.
So, in this case, this rule comes to check between bitwise operators and between logical operators.
This rule ignores other operators.
Examples of incorrect code for this rule with {"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]}
option:
/*eslint no-mixed-operators: ["error", {"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]}]*/
var foo = a && b < 0 || c > 0 || d + 1 === 0;
var foo = a & b | c;
Examples of correct code for this rule with {"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]}
option:
/*eslint no-mixed-operators: ["error", {"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]}]*/
var foo = a || b > 0 || c + 1 === 0;
var foo = a && b > 0 && c + 1 === 0;
var foo = (a && b < 0) || c > 0 || d + 1 === 0;
var foo = a && (b < 0 || c > 0 || d + 1 === 0);
var foo = (a & b) | c;
var foo = a & (b | c);
var foo = a + b * c;
var foo = a + (b * c);
var foo = (a + b) * c;
allowSamePrecedence
Examples of correct code for this rule with {"allowSamePrecedence": true}
option:
/*eslint no-mixed-operators: ["error", {"allowSamePrecedence": true}]*/
// + and - have the same precedence.
var foo = a + b - c;
Examples of incorrect code for this rule with {"allowSamePrecedence": false}
option:
/*eslint no-mixed-operators: ["error", {"allowSamePrecedence": false}]*/
// + and - have the same precedence.
var foo = a + b - c;
When Not To Use It
If you don't want to be notified about mixed operators, then it's safe to disable this rule.
Related Rules
- [no-extra-parens](no-extra-parens.md) Source: http://eslint.org/docs/rules/
Expected to return a value at the end of function 'transformIntoStyleSheetObject'. Open
export default function transformIntoStyleSheetObject(expr, context, transformOptions) {
- Read upRead up
- Exclude checks
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/
Unexpected mix of '||' and '&&'. Open
assert(t.isIdentifier(key) || t.isLiteral(key) && typeof key.value === 'string', 'key must be a string or identifier');
- Read upRead up
- Exclude checks
Disallow mixes of different operators (no-mixed-operators)
Enclosing complex expressions by parentheses clarifies the developer's intention, which makes the code more readable. This rule warns when different operators are used consecutively without parentheses in an expression.
var foo = a && b || c || d; /*BAD: Unexpected mix of '&&' and '||'.*/
var foo = (a && b) || c || d; /*GOOD*/
var foo = a && (b || c || d); /*GOOD*/
Rule Details
This rule checks BinaryExpression
and LogicalExpression
.
This rule may conflict with [no-extra-parens](no-extra-parens.md) rule.
If you use both this and [no-extra-parens](no-extra-parens.md) rule together, you need to use the nestedBinaryExpressions
option of [no-extra-parens](no-extra-parens.md) rule.
Examples of incorrect code for this rule:
/*eslint no-mixed-operators: "error"*/
var foo = a && b < 0 || c > 0 || d + 1 === 0;
var foo = a + b * c;
Examples of correct code for this rule:
/*eslint no-mixed-operators: "error"*/
var foo = a || b || c;
var foo = a && b && c;
var foo = (a && b < 0) || c > 0 || d + 1 === 0;
var foo = a && (b < 0 || c > 0 || d + 1 === 0);
var foo = a + (b * c);
var foo = (a + b) * c;
Options
{
"no-mixed-operators": [
"error",
{
"groups": [
["+", "-", "*", "/", "%", "**"],
["&", "|", "^", "~", "<<", ">>", ">>>"],
["==", "!=", "===", "!==", ">", ">=", "<", "<="],
["&&", "||"],
["in", "instanceof"]
],
"allowSamePrecedence": true
}
]
}
This rule has 2 options.
-
groups
(string[][]
) - specifies groups to compare operators. When this rule compares two operators, if both operators are included in a same group, this rule checks it. Otherwise, this rule ignores it. This value is a list of groups. The group is a list of binary operators. Default is the groups for each kind of operators. -
allowSamePrecedence
(boolean
) - specifies to allow mix of 2 operators if those have the same precedence. Default istrue
.
groups
The following operators can be used in groups
option:
- Arithmetic Operators:
"+"
,"-"
,"*"
,"/"
,"%"
,"**"
- Bitwise Operators:
"&"
,"|"
,"^"
,"~"
,"<<"
,">>"
,">>>"
- Comparison Operators:
"=="
,"!="
,"==="
,"!=="
,">"
,">="
,"<"
,"<="
- Logical Operators:
"&&"
,"||"
- Relational Operators:
"in"
,"instanceof"
Now, considers about {"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]}
configure.
This configure has 2 groups: bitwise operators and logical operators.
This rule checks only if both operators are included in a same group.
So, in this case, this rule comes to check between bitwise operators and between logical operators.
This rule ignores other operators.
Examples of incorrect code for this rule with {"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]}
option:
/*eslint no-mixed-operators: ["error", {"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]}]*/
var foo = a && b < 0 || c > 0 || d + 1 === 0;
var foo = a & b | c;
Examples of correct code for this rule with {"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]}
option:
/*eslint no-mixed-operators: ["error", {"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]}]*/
var foo = a || b > 0 || c + 1 === 0;
var foo = a && b > 0 && c + 1 === 0;
var foo = (a && b < 0) || c > 0 || d + 1 === 0;
var foo = a && (b < 0 || c > 0 || d + 1 === 0);
var foo = (a & b) | c;
var foo = a & (b | c);
var foo = a + b * c;
var foo = a + (b * c);
var foo = (a + b) * c;
allowSamePrecedence
Examples of correct code for this rule with {"allowSamePrecedence": true}
option:
/*eslint no-mixed-operators: ["error", {"allowSamePrecedence": true}]*/
// + and - have the same precedence.
var foo = a + b - c;
Examples of incorrect code for this rule with {"allowSamePrecedence": false}
option:
/*eslint no-mixed-operators: ["error", {"allowSamePrecedence": false}]*/
// + and - have the same precedence.
var foo = a + b - c;
When Not To Use It
If you don't want to be notified about mixed operators, then it's safe to disable this rule.
Related Rules
- [no-extra-parens](no-extra-parens.md) Source: http://eslint.org/docs/rules/
Unnecessary escape character: [. Open
const isStandaloneSelector = /^[:\[]/;
- Read upRead up
- Exclude checks
Disallow unnecessary escape usage (no-useless-escape)
Escaping non-special characters in strings, template literals, and regular expressions doesn't have any effect, as demonstrated in the following example:
let foo = "hol\a"; // > foo = "hola"
let bar = `${foo}\!`; // > bar = "hola!"
let baz = /\:/ // same functionality with /:/
Rule Details
This rule flags escapes that can be safely removed without changing behavior.
Examples of incorrect code for this rule:
/*eslint no-useless-escape: "error"*/
"\'";
'\"';
"\#";
"\e";
`\"`;
`\"${foo}\"`;
`\#{foo}`;
/\!/;
/\@/;
Examples of correct code for this rule:
/*eslint no-useless-escape: "error"*/
"\"";
'\'';
"\x12";
"\u00a9";
"\371";
"xs\u2111";
`\``;
`\${${foo}\}`;
`$\{${foo}\}`;
/\\/g;
/\t/g;
/\w\$\*\^\./;
When Not To Use It
If you don't want to be notified about unnecessary escapes, you can safely disable this rule. Source: http://eslint.org/docs/rules/
Unnecessary escape character: .. Open
const isValidStyleName = /^([_a-zA-Z]+[ _a-zA-Z0-9-]*[_a-zA-Z0-9-]*)|(\$[_a-zA-Z0-9-\s,\.]+)$/;
- Read upRead up
- Exclude checks
Disallow unnecessary escape usage (no-useless-escape)
Escaping non-special characters in strings, template literals, and regular expressions doesn't have any effect, as demonstrated in the following example:
let foo = "hol\a"; // > foo = "hola"
let bar = `${foo}\!`; // > bar = "hola!"
let baz = /\:/ // same functionality with /:/
Rule Details
This rule flags escapes that can be safely removed without changing behavior.
Examples of incorrect code for this rule:
/*eslint no-useless-escape: "error"*/
"\'";
'\"';
"\#";
"\e";
`\"`;
`\"${foo}\"`;
`\#{foo}`;
/\!/;
/\@/;
Examples of correct code for this rule:
/*eslint no-useless-escape: "error"*/
"\"";
'\'';
"\x12";
"\u00a9";
"\371";
"xs\u2111";
`\``;
`\${${foo}\}`;
`$\{${foo}\}`;
/\\/g;
/\t/g;
/\w\$\*\^\./;
When Not To Use It
If you don't want to be notified about unnecessary escapes, you can safely disable this rule. Source: http://eslint.org/docs/rules/
Unexpected string concatenation. Open
return '_' + keys.length.toString(36).split('').reverse().join('');
- Read upRead up
- 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
value = '' + value + 'px';
- Read upRead up
- 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
result += options.prefixes.map(p => p.replace(invalidChars, '_')).join('-') + '-';
- Read upRead up
- 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
css.push(indent(level) + selector + ' {');
- Read upRead up
- 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 require(). Open
contextFileCache[file] = require(file);
- Read upRead up
- Exclude checks
Enforce require() on the top-level module scope (global-require)
In Node.js, module dependencies are included using the require()
function, such as:
var fs = require("fs");
While require()
may be called anywhere in code, some style guides prescribe that it should be called only in the top level of a module to make it easier to identify dependencies. For instance, it's arguably harder to identify dependencies when they are deeply nested inside of functions and other statements:
function foo() {
if (condition) {
var fs = require("fs");
}
}
Since require()
does a synchronous load, it can cause performance problems when used in other locations.
Further, ES6 modules mandate that import
and export
statements can only occur in the top level of the module's body.
Rule Details
This rule requires all calls to require()
to be at the top level of the module, similar to ES6 import
and export
statements, which also can occur only at the top level.
Examples of incorrect code for this rule:
/*eslint global-require: "error"*/
/*eslint-env es6*/
// calling require() inside of a function is not allowed
function readFile(filename, callback) {
var fs = require('fs');
fs.readFile(filename, callback)
}
// conditional requires like this are also not allowed
if (DEBUG) { require('debug'); }
// a require() in a switch statement is also flagged
switch(x) { case '1': require('1'); break; }
// you may not require() inside an arrow function body
var getModule = (name) => require(name);
// you may not require() inside of a function body as well
function getModule(name) { return require(name); }
// you may not require() inside of a try/catch block
try {
require(unsafeModule);
} catch(e) {
console.log(e);
}
Examples of correct code for this rule:
/*eslint global-require: "error"*/
// all these variations of require() are ok
require('x');
var y = require('y');
var z;
z = require('z').initialize();
// requiring a module and using it in a function is ok
var fs = require('fs');
function readFile(filename, callback) {
fs.readFile(filename, callback)
}
// you can use a ternary to determine which module to require
var logger = DEBUG ? require('dev-logger') : require('logger');
// if you want you can require() at the end of your module
function doSomethingA() {}
function doSomethingB() {}
var x = require("x"),
z = require("z");
When Not To Use It
If you have a module that must be initialized with information that comes from the file-system or if a module is only used in very rare situations and will cause significant overhead to load it may make sense to disable the rule. If you need to require()
an optional dependency inside of a try
/catch
, you can disable this rule for just that dependency using the // eslint-disable-line global-require
comment.
Source: http://eslint.org/docs/rules/
Do not access Object.prototype method 'hasOwnProperty' from target object. Open
} else if (t.isIdentifier(expr) && context.hasOwnProperty(expr.name)) {
- Read upRead up
- Exclude checks
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 Object.prototype
methods directly from an object.
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 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/