ghost_result = void 0, balloon_result = void 0;

Close

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.

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 to true will allow you to use short circuit evaluations in your expressions (Default: false).
• allowTernary set to true will enable you to use ternary operators in your expressions similarly to short circuit evaluations (Default: false).
• allowTaggedTemplates set to true 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/

                ghost_result = void 0, balloon_result = void 0;

Close

Disallow Use of the Comma Operator (no-sequences)

The comma operator includes multiple expressions where only one is expected. It evaluates each operand from left to right and returns the value of the last operand. However, this frequently obscures side effects, and its use is often an accident. Here are some examples of sequences:

var a = (3, 5); // a = 5

a = b += 5, a + b;

while (a = next(), a && a.length);

(0, eval)("doSomething();");

Rule Details

This rule forbids the use of the comma operator, with the following exceptions:

• In the initialization or update portions of a for statement.
• If the expression sequence is explicitly wrapped in parentheses.

Examples of incorrect code for this rule:

/*eslint no-sequences: "error"*/

foo = doSomething(), val;

0, eval("doSomething();");

do {} while (doSomething(), !!test);

for (; doSomething(), !!test; );

if (doSomething(), !!test);

switch (val = foo(), val) {}

while (val = foo(), val < 42);

with (doSomething(), val) {}

Examples of correct code for this rule:

/*eslint no-sequences: "error"*/

foo = (doSomething(), val);

(0, eval)("doSomething();");

do {} while ((doSomething(), !!test));

for (i = 0, j = 10; i < j; i++, j--);

if ((doSomething(), !!test));

switch ((val = foo(), val)) {}

while ((val = foo(), val < 42));

// with ((doSomething(), val)) {}

When Not To Use It

Disable this rule if sequence expressions with the comma operator are acceptable. Source: http://eslint.org/docs/rules/

                ghost_result = void 0, balloon_result = void 0;

Close

Disallow use of the void operator. (no-void)

The void operator takes an operand and returns undefined: void expression will evaluate expression and return undefined. It can be used to ignore any side effects expression may produce:

The common case of using void operator is to get a "pure" undefined value as prior to ES5 the undefined variable was mutable:

// will always return undefined
(function(){
    return void 0;
})();

// will return 1 in ES3 and undefined in ES5+
(function(){
    undefined = 1;
    return undefined;
})();

// will throw TypeError in ES5+
(function(){
    'use strict';
    undefined = 1;
})();

Another common case is to minify code as void 0 is shorter than undefined:

foo = void 0;
foo = undefined;

When used with IIFE (immediately-invoked function expression), void can be used to force the function keyword to be treated as an expression instead of a declaration:

var foo = 1;
void function(){ foo = 1; }() // will assign foo a value of 1
+function(){ foo = 1; }() // same as above

function(){ foo = 1; }() // will throw SyntaxError

Some code styles prohibit void operator, marking it as non-obvious and hard to read.

Rule Details

This rule aims to eliminate use of void operator.

Examples of incorrect code for this rule:

/*eslint no-void: "error"*/

void foo

var foo = void bar();

When Not To Use It

If you intentionally use the void operator then you can disable this rule.

Further Reading

• Mozilla Developer Network
• Bad Parts: Appendix B - JavaScript: The Good Parts by Douglas Crockford

Related Rules

• [no-undef-init](no-undef-init.md)
• [no-undefined](no-undefined.md) Source: http://eslint.org/docs/rules/

    ,

Close

Comma style (comma-style)

The Comma Style rule enforces styles for comma-separated lists. There are two comma styles primarily used in JavaScript:

• The standard style, in which commas are placed at the end of the current line
• Comma First style, in which commas are placed at the start of the next line

One of the justifications for using Comma First style is that it can help track missing and trailing commas. These are problematic because missing commas in variable declarations can lead to the leakage of global variables and trailing commas can lead to errors in older versions of IE.

Rule Details

This rule enforce consistent comma style in array literals, object literals, and variable declarations.

This rule does not apply in either of the following cases:

• comma preceded and followed by linebreak (lone comma)
• single-line array literals, object literals, and variable declarations

Options

This rule has a string option:

• "last" (default) requires a comma after and on the same line as an array element, object property, or variable declaration
• "first" requires a comma before and on the same line as an array element, object property, or variable declaration

This rule also accepts an additional exceptions object:

• "exceptions" has properties whose names correspond to node types in the abstract syntax tree (AST) of JavaScript code:

  • "ArrayExpression": true ignores comma style in array literals
  • "ArrayPattern": true ignores comma style in array patterns of destructuring
  • "ArrowFunctionExpression": true ignores comma style in the parameters of arrow function expressions
  • "CallExpression": true ignores comma style in the arguments of function calls
  • "FunctionDeclaration": true ignores comma style in the parameters of function declarations
  • "FunctionExpression": true ignores comma style in the parameters of function expressions
  • "ImportDeclaration": true ignores comma style in the specifiers of import declarations
  • "ObjectExpression": true ignores comma style in object literals
  • "ObjectPattern": true ignores comma style in object patterns of destructuring
  • "VariableDeclaration": true ignores comma style in variable declarations

A way to determine the node types as defined by ESTree is to use the online demo.

last

Examples of incorrect code for this rule with the default "last" option:

/*eslint comma-style: ["error", "last"]*/

var foo = 1
,
bar = 2;

var foo = 1
  , bar = 2;

var foo = ["apples"
           , "oranges"];

function bar() {
    return {
        "a": 1
        ,"b:": 2
    };
}

Examples of correct code for this rule with the default "last" option:

/*eslint comma-style: ["error", "last"]*/

var foo = 1, bar = 2;

var foo = 1,
    bar = 2;

var foo = ["apples",
           "oranges"];

function bar() {
    return {
        "a": 1,
        "b:": 2
    };
}

first

Examples of incorrect code for this rule with the "first" option:

/*eslint comma-style: ["error", "first"]*/

var foo = 1,
    bar = 2;

var foo = ["apples",
           "oranges"];

function bar() {
    return {
        "a": 1,
        "b:": 2
    };
}

Examples of correct code for this rule with the "first" option:

/*eslint comma-style: ["error", "first"]*/

var foo = 1, bar = 2;

var foo = 1
    ,bar = 2;

var foo = ["apples"
          ,"oranges"];

function bar() {
    return {
        "a": 1
        ,"b:": 2
    };
}

exceptions

An example use case is to enforce comma style only in var statements.

Examples of incorrect code for this rule with sample "first", { "exceptions": { … } } options:

/*eslint comma-style: ["error", "first", { "exceptions": { "ArrayExpression": true, "ObjectExpression": true } }]*/

var o = {},
    a = [];

Examples of correct code for this rule with sample "first", { "exceptions": { … } } options:

/*eslint comma-style: ["error", "first", { "exceptions": { "ArrayExpression": true, "ObjectExpression": true } }]*/

var o = {fst:1,
         snd: [1,
               2]}
  , a = [];

When Not To Use It

This rule can safely be turned off if your project does not care about enforcing a consistent comma style.

Further Reading

For more information on the Comma First style:

• A better coding convention for lists and object literals in JavaScript by isaacs
• npm coding style guideline

Related Rules

• [operator-linebreak](operator-linebreak.md) Source: http://eslint.org/docs/rules/

     * デフォルトのゴーストのビュークラス

Close

enforce consistent linebreak style (linebreak-style)

When developing with a lot of people all having different editors, VCS applications and operating systems it may occur that different line endings are written by either of the mentioned (might especially happen when using the windows and mac versions of SourceTree together).

The linebreaks (new lines) used in windows operating system are usually carriage returns (CR) followed by a line feed (LF) making it a carriage return line feed (CRLF) whereas Linux and Unix use a simple line feed (LF). The corresponding control sequences are "\n" (for LF) and "\r\n" for (CRLF).

Many versioning systems (like git and subversion) can automatically ensure the correct ending. However to cover all contingencies, you can activate this rule.

Rule Details

This rule enforces consistent line endings independent of operating system, VCS, or editor used across your codebase.

Options

This rule has a string option:

• "unix" (default) enforces the usage of Unix line endings: \n for LF.
• "windows" enforces the usage of Windows line endings: \r\n for CRLF.

unix

Examples of incorrect code for this rule with the default "unix" option:

/*eslint linebreak-style: ["error", "unix"]*/

var a = 'a'; // \r\n

Examples of correct code for this rule with the default "unix" option:

/*eslint linebreak-style: ["error", "unix"]*/

var a = 'a', // \n
    b = 'b'; // \n
// \n
function foo(params) { // \n
    // do stuff \n
}// \n

windows

Examples of incorrect code for this rule with the "windows" option:

/*eslint linebreak-style: ["error", "windows"]*/

var a = 'a'; // \n

Examples of correct code for this rule with the "windows" option:

/*eslint linebreak-style: ["error", "windows"]*/

var a = 'a', // \r\n
    b = 'b'; // \r\n
// \r\n
function foo(params) { // \r\n
    // do stuff \r\n
} // \r\n

Using this rule with version control systems

Version control systems sometimes have special behavior for linebreaks. To make it easy for developers to contribute to your codebase from different platforms, you may want to configure your VCS to handle linebreaks appropriately.

For example, the default behavior of git on Windows systems is to convert LF linebreaks to CRLF when checking out files, but to store the linebreaks as LF when committing a change. This will cause the linebreak-style rule to report errors if configured with the "unix" setting, because the files that ESLint sees will have CRLF linebreaks. If you use git, you may want to add a line to your .gitattributes file to prevent git from converting linebreaks in .js files:

*.js text eol=lf

When Not To Use It

If you aren't concerned about having different line endings within your code, then you can safely turn this rule off.

Compatibility

• JSCS: validateLineBreaks Source: http://eslint.org/docs/rules/

    /**

Close

enforce consistent linebreak style (linebreak-style)

When developing with a lot of people all having different editors, VCS applications and operating systems it may occur that different line endings are written by either of the mentioned (might especially happen when using the windows and mac versions of SourceTree together).

The linebreaks (new lines) used in windows operating system are usually carriage returns (CR) followed by a line feed (LF) making it a carriage return line feed (CRLF) whereas Linux and Unix use a simple line feed (LF). The corresponding control sequences are "\n" (for LF) and "\r\n" for (CRLF).

Many versioning systems (like git and subversion) can automatically ensure the correct ending. However to cover all contingencies, you can activate this rule.

Rule Details

This rule enforces consistent line endings independent of operating system, VCS, or editor used across your codebase.

Options

This rule has a string option:

• "unix" (default) enforces the usage of Unix line endings: \n for LF.
• "windows" enforces the usage of Windows line endings: \r\n for CRLF.

unix

Examples of incorrect code for this rule with the default "unix" option:

/*eslint linebreak-style: ["error", "unix"]*/

var a = 'a'; // \r\n

Examples of correct code for this rule with the default "unix" option:

/*eslint linebreak-style: ["error", "unix"]*/

var a = 'a', // \n
    b = 'b'; // \n
// \n
function foo(params) { // \n
    // do stuff \n
}// \n

windows

Examples of incorrect code for this rule with the "windows" option:

/*eslint linebreak-style: ["error", "windows"]*/

var a = 'a'; // \n

Examples of correct code for this rule with the "windows" option:

/*eslint linebreak-style: ["error", "windows"]*/

var a = 'a', // \r\n
    b = 'b'; // \r\n
// \r\n
function foo(params) { // \r\n
    // do stuff \r\n
} // \r\n

Using this rule with version control systems

Version control systems sometimes have special behavior for linebreaks. To make it easy for developers to contribute to your codebase from different platforms, you may want to configure your VCS to handle linebreaks appropriately.

For example, the default behavior of git on Windows systems is to convert LF linebreaks to CRLF when checking out files, but to store the linebreaks as LF when committing a change. This will cause the linebreak-style rule to report errors if configured with the "unix" setting, because the files that ESLint sees will have CRLF linebreaks. If you use git, you may want to add a line to your .gitattributes file to prevent git from converting linebreaks in .js files:

*.js text eol=lf

When Not To Use It

If you aren't concerned about having different line endings within your code, then you can safely turn this rule off.

Compatibility

• JSCS: validateLineBreaks Source: http://eslint.org/docs/rules/

     * @type {cuttlebone}

Close

enforce consistent linebreak style (linebreak-style)

When developing with a lot of people all having different editors, VCS applications and operating systems it may occur that different line endings are written by either of the mentioned (might especially happen when using the windows and mac versions of SourceTree together).

The linebreaks (new lines) used in windows operating system are usually carriage returns (CR) followed by a line feed (LF) making it a carriage return line feed (CRLF) whereas Linux and Unix use a simple line feed (LF). The corresponding control sequences are "\n" (for LF) and "\r\n" for (CRLF).

Many versioning systems (like git and subversion) can automatically ensure the correct ending. However to cover all contingencies, you can activate this rule.

Rule Details

This rule enforces consistent line endings independent of operating system, VCS, or editor used across your codebase.

Options

This rule has a string option:

• "unix" (default) enforces the usage of Unix line endings: \n for LF.
• "windows" enforces the usage of Windows line endings: \r\n for CRLF.

unix

Examples of incorrect code for this rule with the default "unix" option:

/*eslint linebreak-style: ["error", "unix"]*/

var a = 'a'; // \r\n

Examples of correct code for this rule with the default "unix" option:

/*eslint linebreak-style: ["error", "unix"]*/

var a = 'a', // \n
    b = 'b'; // \n
// \n
function foo(params) { // \n
    // do stuff \n
}// \n

windows

Examples of incorrect code for this rule with the "windows" option:

/*eslint linebreak-style: ["error", "windows"]*/

var a = 'a'; // \n

Examples of correct code for this rule with the "windows" option:

/*eslint linebreak-style: ["error", "windows"]*/

var a = 'a', // \r\n
    b = 'b'; // \r\n
// \r\n
function foo(params) { // \r\n
    // do stuff \r\n
} // \r\n

Using this rule with version control systems

Version control systems sometimes have special behavior for linebreaks. To make it easy for developers to contribute to your codebase from different platforms, you may want to configure your VCS to handle linebreaks appropriately.

For example, the default behavior of git on Windows systems is to convert LF linebreaks to CRLF when checking out files, but to store the linebreaks as LF when committing a change. This will cause the linebreak-style rule to report errors if configured with the "unix" setting, because the files that ESLint sees will have CRLF linebreaks. If you use git, you may want to add a line to your .gitattributes file to prevent git from converting linebreaks in .js files:

*.js text eol=lf

When Not To Use It

If you aren't concerned about having different line endings within your code, then you can safely turn this rule off.

Compatibility

• JSCS: validateLineBreaks Source: http://eslint.org/docs/rules/

            switch (_context10.prev = _context10.next) {

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/

              case 3:

Close

Disallow Magic Numbers (no-magic-numbers)

'Magic numbers' are numbers that occur multiple time in code without an explicit meaning. They should preferably be replaced by named constants.

var now = Date.now(),
    inOneHour = now + (60 * 60 * 1000);

Rule Details

The no-magic-numbers rule aims to make code more readable and refactoring easier by ensuring that special numbers are declared as constants to make their meaning explicit.

Examples of incorrect code for this rule:

/*eslint no-magic-numbers: "error"*/

var dutyFreePrice = 100,
    finalPrice = dutyFreePrice + (dutyFreePrice * 0.25);

/*eslint no-magic-numbers: "error"*/

var data = ['foo', 'bar', 'baz'];

var dataLast = data[2];

/*eslint no-magic-numbers: "error"*/

var SECONDS;

SECONDS = 60;

Examples of correct code for this rule:

/*eslint no-magic-numbers: "error"*/

var TAX = 0.25;

var dutyFreePrice = 100,
    finalPrice = dutyFreePrice + (dutyFreePrice * TAX);

Options

ignore

An array of numbers to ignore. It's set to [] by default. If provided, it must be an Array.

Examples of correct code for the sample { "ignore": [1] } option:

/*eslint no-magic-numbers: ["error", { "ignore": [1] }]*/

var data = ['foo', 'bar', 'baz'];
var dataLast = data.length && data[data.length - 1];

ignoreArrayIndexes

A boolean to specify if numbers used as array indexes are considered okay. false by default.

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

/*eslint no-magic-numbers: ["error", { "ignoreArrayIndexes": true }]*/

var data = ['foo', 'bar', 'baz'];
var dataLast = data[2];

enforceConst

A boolean to specify if we should check for the const keyword in variable declaration of numbers. false by default.

Examples of incorrect code for the { "enforceConst": true } option:

/*eslint no-magic-numbers: ["error", { "enforceConst": true }]*/

var TAX = 0.25;

var dutyFreePrice = 100,
    finalPrice = dutyFreePrice + (dutyFreePrice * TAX);

detectObjects

A boolean to specify if we should detect numbers when setting object properties for example. false by default.

Examples of incorrect code for the { "detectObjects": true } option:

/*eslint no-magic-numbers: ["error", { "detectObjects": true }]*/

var magic = {
  tax: 0.25
};

var dutyFreePrice = 100,
    finalPrice = dutyFreePrice + (dutyFreePrice * magic.tax);

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

/*eslint no-magic-numbers: ["error", { "detectObjects": true }]*/

var TAX = 0.25;

var magic = {
  tax: TAX
};

var dutyFreePrice = 100,
    finalPrice = dutyFreePrice + (dutyFreePrice * magic.tax);

Source: http://eslint.org/docs/rules/

                  _context11.next = 10;

Close

Disallow Reassignment of Function Parameters (no-param-reassign)

Assignment to variables declared as function parameters can be misleading and lead to confusing behavior, as modifying function parameters will also mutate the arguments object. Often, assignment to function parameters is unintended and indicative of a mistake or programmer error.

This rule can be also configured to fail when function parameters are modified. Side effects on parameters can cause counter-intuitive execution flow and make errors difficult to track down.

Rule Details

This rule aims to prevent unintended behavior caused by modification or reassignment of function parameters.

Examples of incorrect code for this rule:

/*eslint no-param-reassign: "error"*/

function foo(bar) {
    bar = 13;
}

function foo(bar) {
    bar++;
}

Examples of correct code for this rule:

/*eslint no-param-reassign: "error"*/

function foo(bar) {
    var baz = bar;
}

Options

This rule takes one option, an object, with a boolean property "props" and an array "ignorePropertyModificationsFor". "props" is false by default. If "props" is set to true, this rule warns against the modification of parameter properties unless they're included in "ignorePropertyModificationsFor", which is an empty array by default.

props

Examples of correct code for the default { "props": false } option:

/*eslint no-param-reassign: ["error", { "props": false }]*/

function foo(bar) {
    bar.prop = "value";
}

function foo(bar) {
    delete bar.aaa;
}

function foo(bar) {
    bar.aaa++;
}

Examples of incorrect code for the { "props": true } option:

/*eslint no-param-reassign: ["error", { "props": true }]*/

function foo(bar) {
    bar.prop = "value";
}

function foo(bar) {
    delete bar.aaa;
}

function foo(bar) {
    bar.aaa++;
}

Examples of correct code for the { "props": true } option with "ignorePropertyModificationsFor" set:

/*eslint no-param-reassign: ["error", { "props": true, "ignorePropertyModificationsFor": ["bar"] }]*/

function foo(bar) {
    bar.prop = "value";
}

function foo(bar) {
    delete bar.aaa;
}

function foo(bar) {
    bar.aaa++;
}

When Not To Use It

If you want to allow assignment to function parameters, then you can safely disable this rule.

Further Reading

• JavaScript: Don’t Reassign Your Function Arguments Source: http://eslint.org/docs/rules/

              case 16:

Close

Disallow Magic Numbers (no-magic-numbers)

'Magic numbers' are numbers that occur multiple time in code without an explicit meaning. They should preferably be replaced by named constants.

var now = Date.now(),
    inOneHour = now + (60 * 60 * 1000);

Rule Details

The no-magic-numbers rule aims to make code more readable and refactoring easier by ensuring that special numbers are declared as constants to make their meaning explicit.

Examples of incorrect code for this rule:

/*eslint no-magic-numbers: "error"*/

var dutyFreePrice = 100,
    finalPrice = dutyFreePrice + (dutyFreePrice * 0.25);

/*eslint no-magic-numbers: "error"*/

var data = ['foo', 'bar', 'baz'];

var dataLast = data[2];

/*eslint no-magic-numbers: "error"*/

var SECONDS;

SECONDS = 60;

Examples of correct code for this rule:

/*eslint no-magic-numbers: "error"*/

var TAX = 0.25;

var dutyFreePrice = 100,
    finalPrice = dutyFreePrice + (dutyFreePrice * TAX);

Options

ignore

An array of numbers to ignore. It's set to [] by default. If provided, it must be an Array.

Examples of correct code for the sample { "ignore": [1] } option:

/*eslint no-magic-numbers: ["error", { "ignore": [1] }]*/

var data = ['foo', 'bar', 'baz'];
var dataLast = data.length && data[data.length - 1];

ignoreArrayIndexes

A boolean to specify if numbers used as array indexes are considered okay. false by default.

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

/*eslint no-magic-numbers: ["error", { "ignoreArrayIndexes": true }]*/

var data = ['foo', 'bar', 'baz'];
var dataLast = data[2];

enforceConst

A boolean to specify if we should check for the const keyword in variable declaration of numbers. false by default.

Examples of incorrect code for the { "enforceConst": true } option:

/*eslint no-magic-numbers: ["error", { "enforceConst": true }]*/

var TAX = 0.25;

var dutyFreePrice = 100,
    finalPrice = dutyFreePrice + (dutyFreePrice * TAX);

detectObjects

A boolean to specify if we should detect numbers when setting object properties for example. false by default.

Examples of incorrect code for the { "detectObjects": true } option:

/*eslint no-magic-numbers: ["error", { "detectObjects": true }]*/

var magic = {
  tax: 0.25
};

var dutyFreePrice = 100,
    finalPrice = dutyFreePrice + (dutyFreePrice * magic.tax);

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

/*eslint no-magic-numbers: ["error", { "detectObjects": true }]*/

var TAX = 0.25;

var magic = {
  tax: TAX
};

var dutyFreePrice = 100,
    finalPrice = dutyFreePrice + (dutyFreePrice * magic.tax);

Source: http://eslint.org/docs/rules/

                this.emit('install_nar_loaded', target, nar);

Close

Disallow this keywords outside of classes or class-like objects. (no-invalid-this)

Under the strict mode, this keywords outside of classes or class-like objects might be undefined and raise a TypeError.

Rule Details

This rule aims to flag usage of this keywords outside of classes or class-like objects.

Basically this rule checks whether or not a function which are containing this keywords is a constructor or a method.

This rule judges from following conditions whether or not the function is a constructor:

• The name of the function starts with uppercase.
• The function is assigned to a variable which starts with an uppercase letter.
• The function is a constructor of ES2015 Classes.

This rule judges from following conditions whether or not the function is a method:

• The function is on an object literal.
• The function is assigned to a property.
• The function is a method/getter/setter of ES2015 Classes. (excepts static methods)

And this rule allows this keywords in functions below:

• The call/apply/bind method of the function is called directly.
• The function is a callback of array methods (such as .forEach()) if thisArg is given.
• The function has @this tag in its JSDoc comment.

Otherwise are considered problems.

This rule applies only in strict mode. With "parserOptions": { "sourceType": "module" } in the ESLint configuration, your code is in strict mode even without a "use strict" directive.

Examples of incorrect code for this rule in strict mode:

/*eslint no-invalid-this: "error"*/
/*eslint-env es6*/

"use strict";

this.a = 0;
baz(() => this);

(function() {
    this.a = 0;
    baz(() => this);
})();

function foo() {
    this.a = 0;
    baz(() => this);
}

var foo = function() {
    this.a = 0;
    baz(() => this);
};

foo(function() {
    this.a = 0;
    baz(() => this);
});

obj.foo = () => {
    // `this` of arrow functions is the outer scope's.
    this.a = 0;
};

var obj = {
    aaa: function() {
        return function foo() {
            // There is in a method `aaa`, but `foo` is not a method.
            this.a = 0;
            baz(() => this);
        };
    }
};

foo.forEach(function() {
    this.a = 0;
    baz(() => this);
});

Examples of correct code for this rule in strict mode:

/*eslint no-invalid-this: "error"*/
/*eslint-env es6*/

"use strict";

function Foo() {
    // OK, this is in a legacy style constructor.
    this.a = 0;
    baz(() => this);
}

class Foo {
    constructor() {
        // OK, this is in a constructor.
        this.a = 0;
        baz(() => this);
    }
}

var obj = {
    foo: function foo() {
        // OK, this is in a method (this function is on object literal).
        this.a = 0;
    }
};

var obj = {
    foo() {
        // OK, this is in a method (this function is on object literal).
        this.a = 0;
    }
};

var obj = {
    get foo() {
        // OK, this is in a method (this function is on object literal).
        return this.a;
    }
};

var obj = Object.create(null, {
    foo: {value: function foo() {
        // OK, this is in a method (this function is on object literal).
        this.a = 0;
    }}
});

Object.defineProperty(obj, "foo", {
    value: function foo() {
        // OK, this is in a method (this function is on object literal).
        this.a = 0;
    }
});

Object.defineProperties(obj, {
    foo: {value: function foo() {
        // OK, this is in a method (this function is on object literal).
        this.a = 0;
    }}
});

function Foo() {
    this.foo = function foo() {
        // OK, this is in a method (this function assigns to a property).
        this.a = 0;
        baz(() => this);
    };
}

obj.foo = function foo() {
    // OK, this is in a method (this function assigns to a property).
    this.a = 0;
};

Foo.prototype.foo = function foo() {
    // OK, this is in a method (this function assigns to a property).
    this.a = 0;
};

class Foo {
    foo() {
        // OK, this is in a method.
        this.a = 0;
        baz(() => this);
    }

    static foo() {
        // OK, this is in a method (static methods also have valid this).
        this.a = 0;
        baz(() => this);
    }
}

var foo = (function foo() {
    // OK, the `bind` method of this function is called directly.
    this.a = 0;
}).bind(obj);

foo.forEach(function() {
    // OK, `thisArg` of `.forEach()` is given.
    this.a = 0;
    baz(() => this);
}, thisArg);

/** @this Foo */
function foo() {
    // OK, this function has a `@this` tag in its JSDoc comment.
    this.a = 0;
}

When Not To Use It

If you don't want to be notified about usage of this keyword outside of classes or class-like objects, you can safely disable this rule. Source: http://eslint.org/docs/rules/

                dirpath = void 0, sakuraname = void 0;

Close

Disallow Use of the Comma Operator (no-sequences)

The comma operator includes multiple expressions where only one is expected. It evaluates each operand from left to right and returns the value of the last operand. However, this frequently obscures side effects, and its use is often an accident. Here are some examples of sequences:

var a = (3, 5); // a = 5

a = b += 5, a + b;

while (a = next(), a && a.length);

(0, eval)("doSomething();");

Rule Details

This rule forbids the use of the comma operator, with the following exceptions:

• In the initialization or update portions of a for statement.
• If the expression sequence is explicitly wrapped in parentheses.

Examples of incorrect code for this rule:

/*eslint no-sequences: "error"*/

foo = doSomething(), val;

0, eval("doSomething();");

do {} while (doSomething(), !!test);

for (; doSomething(), !!test; );

if (doSomething(), !!test);

switch (val = foo(), val) {}

while (val = foo(), val < 42);

with (doSomething(), val) {}

Examples of correct code for this rule:

/*eslint no-sequences: "error"*/

foo = (doSomething(), val);

(0, eval)("doSomething();");

do {} while ((doSomething(), !!test));

for (i = 0, j = 10; i < j; i++, j--);

if ((doSomething(), !!test));

switch ((val = foo(), val)) {}

while ((val = foo(), val < 42));

// with ((doSomething(), val)) {}

When Not To Use It

Disable this rule if sequence expressions with the comma operator are acceptable. Source: http://eslint.org/docs/rules/

                  dirpath = typeof from === 'string' || from instanceof String ? from : this.namedId(from);

Close

Disallow this keywords outside of classes or class-like objects. (no-invalid-this)

Under the strict mode, this keywords outside of classes or class-like objects might be undefined and raise a TypeError.

Rule Details

This rule aims to flag usage of this keywords outside of classes or class-like objects.

Basically this rule checks whether or not a function which are containing this keywords is a constructor or a method.

This rule judges from following conditions whether or not the function is a constructor:

• The name of the function starts with uppercase.
• The function is assigned to a variable which starts with an uppercase letter.
• The function is a constructor of ES2015 Classes.

This rule judges from following conditions whether or not the function is a method:

• The function is on an object literal.
• The function is assigned to a property.
• The function is a method/getter/setter of ES2015 Classes. (excepts static methods)

And this rule allows this keywords in functions below:

• The call/apply/bind method of the function is called directly.
• The function is a callback of array methods (such as .forEach()) if thisArg is given.
• The function has @this tag in its JSDoc comment.

Otherwise are considered problems.

This rule applies only in strict mode. With "parserOptions": { "sourceType": "module" } in the ESLint configuration, your code is in strict mode even without a "use strict" directive.

Examples of incorrect code for this rule in strict mode:

/*eslint no-invalid-this: "error"*/
/*eslint-env es6*/

"use strict";

this.a = 0;
baz(() => this);

(function() {
    this.a = 0;
    baz(() => this);
})();

function foo() {
    this.a = 0;
    baz(() => this);
}

var foo = function() {
    this.a = 0;
    baz(() => this);
};

foo(function() {
    this.a = 0;
    baz(() => this);
});

obj.foo = () => {
    // `this` of arrow functions is the outer scope's.
    this.a = 0;
};

var obj = {
    aaa: function() {
        return function foo() {
            // There is in a method `aaa`, but `foo` is not a method.
            this.a = 0;
            baz(() => this);
        };
    }
};

foo.forEach(function() {
    this.a = 0;
    baz(() => this);
});

Examples of correct code for this rule in strict mode:

/*eslint no-invalid-this: "error"*/
/*eslint-env es6*/

"use strict";

function Foo() {
    // OK, this is in a legacy style constructor.
    this.a = 0;
    baz(() => this);
}

class Foo {
    constructor() {
        // OK, this is in a constructor.
        this.a = 0;
        baz(() => this);
    }
}

var obj = {
    foo: function foo() {
        // OK, this is in a method (this function is on object literal).
        this.a = 0;
    }
};

var obj = {
    foo() {
        // OK, this is in a method (this function is on object literal).
        this.a = 0;
    }
};

var obj = {
    get foo() {
        // OK, this is in a method (this function is on object literal).
        return this.a;
    }
};

var obj = Object.create(null, {
    foo: {value: function foo() {
        // OK, this is in a method (this function is on object literal).
        this.a = 0;
    }}
});

Object.defineProperty(obj, "foo", {
    value: function foo() {
        // OK, this is in a method (this function is on object literal).
        this.a = 0;
    }
});

Object.defineProperties(obj, {
    foo: {value: function foo() {
        // OK, this is in a method (this function is on object literal).
        this.a = 0;
    }}
});

function Foo() {
    this.foo = function foo() {
        // OK, this is in a method (this function assigns to a property).
        this.a = 0;
        baz(() => this);
    };
}

obj.foo = function foo() {
    // OK, this is in a method (this function assigns to a property).
    this.a = 0;
};

Foo.prototype.foo = function foo() {
    // OK, this is in a method (this function assigns to a property).
    this.a = 0;
};

class Foo {
    foo() {
        // OK, this is in a method.
        this.a = 0;
        baz(() => this);
    }

    static foo() {
        // OK, this is in a method (static methods also have valid this).
        this.a = 0;
        baz(() => this);
    }
}

var foo = (function foo() {
    // OK, the `bind` method of this function is called directly.
    this.a = 0;
}).bind(obj);

foo.forEach(function() {
    // OK, `thisArg` of `.forEach()` is given.
    this.a = 0;
    baz(() => this);
}, thisArg);

/** @this Foo */
function foo() {
    // OK, this function has a `@this` tag in its JSDoc comment.
    this.a = 0;
}

When Not To Use It

If you don't want to be notified about usage of this keyword outside of classes or class-like objects, you can safely disable this rule. Source: http://eslint.org/docs/rules/

                ghost_result = void 0, balloon_result = void 0;

Close

Disallow use of the void operator. (no-void)

The void operator takes an operand and returns undefined: void expression will evaluate expression and return undefined. It can be used to ignore any side effects expression may produce:

The common case of using void operator is to get a "pure" undefined value as prior to ES5 the undefined variable was mutable:

// will always return undefined
(function(){
    return void 0;
})();

// will return 1 in ES3 and undefined in ES5+
(function(){
    undefined = 1;
    return undefined;
})();

// will throw TypeError in ES5+
(function(){
    'use strict';
    undefined = 1;
})();

Another common case is to minify code as void 0 is shorter than undefined:

foo = void 0;
foo = undefined;

When used with IIFE (immediately-invoked function expression), void can be used to force the function keyword to be treated as an expression instead of a declaration:

var foo = 1;
void function(){ foo = 1; }() // will assign foo a value of 1
+function(){ foo = 1; }() // same as above

function(){ foo = 1; }() // will throw SyntaxError

Some code styles prohibit void operator, marking it as non-obvious and hard to read.

Rule Details

This rule aims to eliminate use of void operator.

Examples of incorrect code for this rule:

/*eslint no-void: "error"*/

void foo

var foo = void bar();

When Not To Use It

If you intentionally use the void operator then you can disable this rule.

Further Reading

• Mozilla Developer Network
• Bad Parts: Appendix B - JavaScript: The Good Parts by Douglas Crockford

Related Rules

• [no-undef-init](no-undef-init.md)
• [no-undefined](no-undefined.md) Source: http://eslint.org/docs/rules/

      var GhostViewClass = arguments.length <= 1 || arguments[1] === undefined ? this.GhostViewClass : arguments[1];

Close

Suggest using the rest parameters instead of arguments (prefer-rest-params)

There are rest parameters in ES2015. We can use that feature for variadic functions instead of the arguments variable.

arguments does not have methods of Array.prototype, so it's a bit of an inconvenience.

Rule Details

This rule is aimed to flag usage of arguments variables.

Examples

Examples of incorrect code for this rule:

function foo() {
    console.log(arguments);
}

function foo(action) {
    var args = Array.prototype.slice.call(arguments, 1);
    action.apply(null, args);
}

function foo(action) {
    var args = [].slice.call(arguments, 1);
    action.apply(null, args);
}

Examples of correct code for this rule:

function foo(...args) {
    console.log(args);
}

function foo(action, ...args) {
    action.apply(null, args); // or `action(...args)`, related to the `prefer-spread` rule.
}

// Note: the implicit arguments can be overwritten.
function foo(arguments) {
    console.log(arguments); // This is the first argument.
}
function foo() {
    var arguments = 0;
    console.log(arguments); // This is a local variable.
}

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 arguments variables, then it's safe to disable this rule.

Related Rules

• [prefer-spread](prefer-spread.md) Source: http://eslint.org/docs/rules/

     * ゴーストのビュークラス

Close

enforce consistent linebreak style (linebreak-style)

When developing with a lot of people all having different editors, VCS applications and operating systems it may occur that different line endings are written by either of the mentioned (might especially happen when using the windows and mac versions of SourceTree together).

The linebreaks (new lines) used in windows operating system are usually carriage returns (CR) followed by a line feed (LF) making it a carriage return line feed (CRLF) whereas Linux and Unix use a simple line feed (LF). The corresponding control sequences are "\n" (for LF) and "\r\n" for (CRLF).

Many versioning systems (like git and subversion) can automatically ensure the correct ending. However to cover all contingencies, you can activate this rule.

Rule Details

This rule enforces consistent line endings independent of operating system, VCS, or editor used across your codebase.

Options

This rule has a string option:

• "unix" (default) enforces the usage of Unix line endings: \n for LF.
• "windows" enforces the usage of Windows line endings: \r\n for CRLF.

unix

Examples of incorrect code for this rule with the default "unix" option:

/*eslint linebreak-style: ["error", "unix"]*/

var a = 'a'; // \r\n

Examples of correct code for this rule with the default "unix" option:

/*eslint linebreak-style: ["error", "unix"]*/

var a = 'a', // \n
    b = 'b'; // \n
// \n
function foo(params) { // \n
    // do stuff \n
}// \n

windows

Examples of incorrect code for this rule with the "windows" option:

/*eslint linebreak-style: ["error", "windows"]*/

var a = 'a'; // \n

Examples of correct code for this rule with the "windows" option:

/*eslint linebreak-style: ["error", "windows"]*/

var a = 'a', // \r\n
    b = 'b'; // \r\n
// \r\n
function foo(params) { // \r\n
    // do stuff \r\n
} // \r\n

Using this rule with version control systems

Version control systems sometimes have special behavior for linebreaks. To make it easy for developers to contribute to your codebase from different platforms, you may want to configure your VCS to handle linebreaks appropriately.

For example, the default behavior of git on Windows systems is to convert LF linebreaks to CRLF when checking out files, but to store the linebreaks as LF when committing a change. This will cause the linebreak-style rule to report errors if configured with the "unix" setting, because the files that ESLint sees will have CRLF linebreaks. If you use git, you may want to add a line to your .gitattributes file to prevent git from converting linebreaks in .js files:

*.js text eol=lf

When Not To Use It

If you aren't concerned about having different line endings within your code, then you can safely turn this rule off.

Compatibility

• JSCS: validateLineBreaks Source: http://eslint.org/docs/rules/

    value: function () {

Close

Require IIFEs to be Wrapped (wrap-iife)

You can immediately invoke function expressions, but not function declarations. A common technique to create an immediately-invoked function expression (IIFE) is to wrap a function declaration in parentheses. The opening parentheses causes the contained function to be parsed as an expression, rather than a declaration.

// function expression could be unwrapped
var x = function () { return { y: 1 };}();

// function declaration must be wrapped
function () { /* side effects */ }(); // SyntaxError

Rule Details

This rule requires all immediately-invoked function expressions to be wrapped in parentheses.

Options

This rule has two options, a string option and an object option.

String option:

• "outside" enforces always wrapping the call expression. The default is "outside".
• "inside" enforces always wrapping the function expression.
• "any" enforces always wrapping, but allows either style.

Object option:

• "functionPrototypeMethods": true additionally enforces wrapping function expressions invoked using .call and .apply. The default is false.

outside

Examples of incorrect code for the default "outside" option:

/*eslint wrap-iife: ["error", "outside"]*/

var x = function () { return { y: 1 };}(); // unwrapped
var x = (function () { return { y: 1 };})(); // wrapped function expression

Examples of correct code for the default "outside" option:

/*eslint wrap-iife: ["error", "outside"]*/

var x = (function () { return { y: 1 };}()); // wrapped call expression

inside

Examples of incorrect code for the "inside" option:

/*eslint wrap-iife: ["error", "inside"]*/

var x = function () { return { y: 1 };}(); // unwrapped
var x = (function () { return { y: 1 };}()); // wrapped call expression

Examples of correct code for the "inside" option:

/*eslint wrap-iife: ["error", "inside"]*/

var x = (function () { return { y: 1 };})(); // wrapped function expression

any

Examples of incorrect code for the "any" option:

/*eslint wrap-iife: ["error", "any"]*/

var x = function () { return { y: 1 };}(); // unwrapped

Examples of correct code for the "any" option:

/*eslint wrap-iife: ["error", "any"]*/

var x = (function () { return { y: 1 };}()); // wrapped call expression
var x = (function () { return { y: 1 };})(); // wrapped function expression

functionPrototypeMethods

Examples of incorrect code for this rule with the "inside", { "functionPrototypeMethods": true } options:

/* eslint wrap-iife: [2, "inside", { functionPrototypeMethods: true }] */

var x = function(){ foo(); }()
var x = (function(){ foo(); }())
var x = function(){ foo(); }.call(bar)
var x = (function(){ foo(); }.call(bar))

Examples of correct code for this rule with the "inside", { "functionPrototypeMethods": true } options:

/* eslint wrap-iife: [2, "inside", { functionPrototypeMethods: true }] */

var x = (function(){ foo(); })()
var x = (function(){ foo(); }).call(bar)

Source: http://eslint.org/docs/rules/

      var _ref13 = (0, _asyncToGenerator3.default)(_regenerator2.default.mark(function _callee11(target) {

Close

Disallow Magic Numbers (no-magic-numbers)

'Magic numbers' are numbers that occur multiple time in code without an explicit meaning. They should preferably be replaced by named constants.

var now = Date.now(),
    inOneHour = now + (60 * 60 * 1000);

Rule Details

The no-magic-numbers rule aims to make code more readable and refactoring easier by ensuring that special numbers are declared as constants to make their meaning explicit.

Examples of incorrect code for this rule:

/*eslint no-magic-numbers: "error"*/

var dutyFreePrice = 100,
    finalPrice = dutyFreePrice + (dutyFreePrice * 0.25);

/*eslint no-magic-numbers: "error"*/

var data = ['foo', 'bar', 'baz'];

var dataLast = data[2];

/*eslint no-magic-numbers: "error"*/

var SECONDS;

SECONDS = 60;

Examples of correct code for this rule:

/*eslint no-magic-numbers: "error"*/

var TAX = 0.25;

var dutyFreePrice = 100,
    finalPrice = dutyFreePrice + (dutyFreePrice * TAX);

Options

ignore

An array of numbers to ignore. It's set to [] by default. If provided, it must be an Array.

Examples of correct code for the sample { "ignore": [1] } option:

/*eslint no-magic-numbers: ["error", { "ignore": [1] }]*/

var data = ['foo', 'bar', 'baz'];
var dataLast = data.length && data[data.length - 1];

ignoreArrayIndexes

A boolean to specify if numbers used as array indexes are considered okay. false by default.

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

/*eslint no-magic-numbers: ["error", { "ignoreArrayIndexes": true }]*/

var data = ['foo', 'bar', 'baz'];
var dataLast = data[2];

enforceConst

A boolean to specify if we should check for the const keyword in variable declaration of numbers. false by default.

Examples of incorrect code for the { "enforceConst": true } option:

/*eslint no-magic-numbers: ["error", { "enforceConst": true }]*/

var TAX = 0.25;

var dutyFreePrice = 100,
    finalPrice = dutyFreePrice + (dutyFreePrice * TAX);

detectObjects

A boolean to specify if we should detect numbers when setting object properties for example. false by default.

Examples of incorrect code for the { "detectObjects": true } option:

/*eslint no-magic-numbers: ["error", { "detectObjects": true }]*/

var magic = {
  tax: 0.25
};

var dutyFreePrice = 100,
    finalPrice = dutyFreePrice + (dutyFreePrice * magic.tax);

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

/*eslint no-magic-numbers: ["error", { "detectObjects": true }]*/

var TAX = 0.25;

var magic = {
  tax: TAX
};

var dutyFreePrice = 100,
    finalPrice = dutyFreePrice + (dutyFreePrice * magic.tax);

Source: http://eslint.org/docs/rules/

        var from = arguments.length <= 1 || arguments[1] === undefined ? null : arguments[1];

Close

Suggest using the rest parameters instead of arguments (prefer-rest-params)

There are rest parameters in ES2015. We can use that feature for variadic functions instead of the arguments variable.

arguments does not have methods of Array.prototype, so it's a bit of an inconvenience.

Rule Details

This rule is aimed to flag usage of arguments variables.

Examples

Examples of incorrect code for this rule:

function foo() {
    console.log(arguments);
}

function foo(action) {
    var args = Array.prototype.slice.call(arguments, 1);
    action.apply(null, args);
}

function foo(action) {
    var args = [].slice.call(arguments, 1);
    action.apply(null, args);
}

Examples of correct code for this rule:

function foo(...args) {
    console.log(args);
}

function foo(action, ...args) {
    action.apply(null, args); // or `action(...args)`, related to the `prefer-spread` rule.
}

// Note: the implicit arguments can be overwritten.
function foo(arguments) {
    console.log(arguments); // This is the first argument.
}
function foo() {
    var arguments = 0;
    console.log(arguments); // This is a local variable.
}

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 arguments variables, then it's safe to disable this rule.

Related Rules

• [prefer-spread](prefer-spread.md) Source: http://eslint.org/docs/rules/