Boolean.prototype.validate = function (value) {

Close

Disallow Extending of Native Objects (no-extend-native)

In JavaScript, you can extend any object, including builtin or "native" objects. Sometimes people change the behavior of these native objects in ways that break the assumptions made about them in other parts of the code.

For example here we are overriding a builtin method that will then affect all Objects, even other builtins.

// seems harmless
Object.prototype.extra = 55;

// loop through some userIds
var users = {
    "123": "Stan",
    "456": "David"
};

// not what you'd expect
for (var id in users) {
    console.log(id); // "123", "456", "extra"
}

A common suggestion to avoid this problem would be to wrap the inside of the for loop with users.hasOwnProperty(id). However, if this rule is strictly enforced throughout your codebase you won't need to take that step.

Rule Details

Disallows directly modifying the prototype of builtin objects.

Examples of incorrect code for this rule:

/*eslint no-extend-native: "error"*/

Object.prototype.a = "a";
Object.defineProperty(Array.prototype, "times", { value: 999 });

Options

This rule accepts an exceptions option, which can be used to specify a list of builtins for which extensions will be allowed.

exceptions

Examples of correct code for the sample { "exceptions": ["Object"] } option:

/*eslint no-extend-native: ["error", { "exceptions": ["Object"] }]*/

Object.prototype.a = "a";

Known Limitations

This rule does not report any of the following less obvious approaches to modify the prototype of builtin objects:

var x = Object;
x.prototype.thing = a;

eval("Array.prototype.forEach = 'muhahaha'");

with(Array) {
    prototype.thing = 'thing';
};

window.Function.prototype.bind = 'tight';

When Not To Use It

You may want to disable this rule when working with polyfills that try to patch older versions of JavaScript with the latest spec, such as those that might Function.prototype.bind or Array.prototype.forEach in a future-friendly way.

Related Rules

• [no-global-assign](no-global-assign.md) Source: http://eslint.org/docs/rules/

        if (parameterValues == null)

Close

Require === and !== (eqeqeq)

It is considered good practice to use the type-safe equality operators === and !== instead of their regular counterparts == and !=.

The reason for this is that == and != do type coercion which follows the rather obscure Abstract Equality Comparison Algorithm. For instance, the following statements are all considered true:

• [] == false
• [] == ![]
• 3 == "03"

If one of those occurs in an innocent-looking statement such as a == b the actual problem is very difficult to spot.

Rule Details

This rule is aimed at eliminating the type-unsafe equality operators.

Examples of incorrect code for this rule:

/*eslint eqeqeq: "error"*/

if (x == 42) { }

if ("" == text) { }

if (obj.getStuff() != undefined) { }

The --fix option on the command line automatically fixes some problems reported by this rule. A problem is only fixed if one of the operands is a typeof expression, or if both operands are literals with the same type.

Options

always

The "always" option (default) enforces the use of === and !== in every situation (except when you opt-in to more specific handling of null [see below]).

Examples of incorrect code for the "always" option:

/*eslint eqeqeq: ["error", "always"]*/

a == b
foo == true
bananas != 1
value == undefined
typeof foo == 'undefined'
'hello' != 'world'
0 == 0
true == true
foo == null

Examples of correct code for the "always" option:

/*eslint eqeqeq: ["error", "always"]*/

a === b
foo === true
bananas !== 1
value === undefined
typeof foo === 'undefined'
'hello' !== 'world'
0 === 0
true === true
foo === null

This rule optionally takes a second argument, which should be an object with the following supported properties:

• "null": Customize how this rule treats null literals. Possible values:
  • always (default) - Always use === or !==.
  • never - Never use === or !== with null.
  • ignore - Do not apply this rule to null.

smart

The "smart" option enforces the use of === and !== except for these cases:

• Comparing two literal values
• Evaluating the value of typeof
• Comparing against null

Examples of incorrect code for the "smart" option:

/*eslint eqeqeq: ["error", "smart"]*/

// comparing two variables requires ===
a == b

// only one side is a literal
foo == true
bananas != 1

// comparing to undefined requires ===
value == undefined

Examples of correct code for the "smart" option:

/*eslint eqeqeq: ["error", "smart"]*/

typeof foo == 'undefined'
'hello' != 'world'
0 == 0
true == true
foo == null

allow-null

Deprecated: Instead of using this option use "always" and pass a "null" option property with value "ignore". This will tell eslint to always enforce strict equality except when comparing with the null literal.

["error", "always", {"null": "ignore"}]

When Not To Use It

If you don't want to enforce a style for using equality operators, then it's safe to disable this rule. Source: http://eslint.org/docs/rules/

            if (value == null)

Close

Require === and !== (eqeqeq)

It is considered good practice to use the type-safe equality operators === and !== instead of their regular counterparts == and !=.

The reason for this is that == and != do type coercion which follows the rather obscure Abstract Equality Comparison Algorithm. For instance, the following statements are all considered true:

• [] == false
• [] == ![]
• 3 == "03"

If one of those occurs in an innocent-looking statement such as a == b the actual problem is very difficult to spot.

Rule Details

This rule is aimed at eliminating the type-unsafe equality operators.

Examples of incorrect code for this rule:

/*eslint eqeqeq: "error"*/

if (x == 42) { }

if ("" == text) { }

if (obj.getStuff() != undefined) { }

The --fix option on the command line automatically fixes some problems reported by this rule. A problem is only fixed if one of the operands is a typeof expression, or if both operands are literals with the same type.

Options

always

The "always" option (default) enforces the use of === and !== in every situation (except when you opt-in to more specific handling of null [see below]).

Examples of incorrect code for the "always" option:

/*eslint eqeqeq: ["error", "always"]*/

a == b
foo == true
bananas != 1
value == undefined
typeof foo == 'undefined'
'hello' != 'world'
0 == 0
true == true
foo == null

Examples of correct code for the "always" option:

/*eslint eqeqeq: ["error", "always"]*/

a === b
foo === true
bananas !== 1
value === undefined
typeof foo === 'undefined'
'hello' !== 'world'
0 === 0
true === true
foo === null

This rule optionally takes a second argument, which should be an object with the following supported properties:

• "null": Customize how this rule treats null literals. Possible values:
  • always (default) - Always use === or !==.
  • never - Never use === or !== with null.
  • ignore - Do not apply this rule to null.

smart

The "smart" option enforces the use of === and !== except for these cases:

• Comparing two literal values
• Evaluating the value of typeof
• Comparing against null

Examples of incorrect code for the "smart" option:

/*eslint eqeqeq: ["error", "smart"]*/

// comparing two variables requires ===
a == b

// only one side is a literal
foo == true
bananas != 1

// comparing to undefined requires ===
value == undefined

Examples of correct code for the "smart" option:

/*eslint eqeqeq: ["error", "smart"]*/

typeof foo == 'undefined'
'hello' != 'world'
0 == 0
true == true
foo == null

allow-null

Deprecated: Instead of using this option use "always" and pass a "null" option property with value "ignore". This will tell eslint to always enforce strict equality except when comparing with the null literal.

["error", "always", {"null": "ignore"}]

When Not To Use It

If you don't want to enforce a style for using equality operators, then it's safe to disable this rule. Source: http://eslint.org/docs/rules/

            if (type == null)

Close

Disallow Null Comparisons (no-eq-null)

Comparing to null without a type-checking operator (== or !=), can have unintended results as the comparison will evaluate to true when comparing to not just a null, but also an undefined value.

if (foo == null) {
  bar();
}

Rule Details

The no-eq-null rule aims reduce potential bug and unwanted behavior by ensuring that comparisons to null only match null, and not also undefined. As such it will flag comparisons to null when using == and !=.

Examples of incorrect code for this rule:

/*eslint no-eq-null: "error"*/

if (foo == null) {
  bar();
}

while (qux != null) {
  baz();
}

Examples of correct code for this rule:

/*eslint no-eq-null: "error"*/

if (foo === null) {
  bar();
}

while (qux !== null) {
  baz();
}

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

            if (value == null)

Close

Disallow Null Comparisons (no-eq-null)

Comparing to null without a type-checking operator (== or !=), can have unintended results as the comparison will evaluate to true when comparing to not just a null, but also an undefined value.

if (foo == null) {
  bar();
}

Rule Details

The no-eq-null rule aims reduce potential bug and unwanted behavior by ensuring that comparisons to null only match null, and not also undefined. As such it will flag comparisons to null when using == and !=.

Examples of incorrect code for this rule:

/*eslint no-eq-null: "error"*/

if (foo == null) {
  bar();
}

while (qux != null) {
  baz();
}

Examples of correct code for this rule:

/*eslint no-eq-null: "error"*/

if (foo === null) {
  bar();
}

while (qux !== null) {
  baz();
}

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

            if (typeof (value) != "number" || isNaN(Number(value)))

Close

Require === and !== (eqeqeq)

It is considered good practice to use the type-safe equality operators === and !== instead of their regular counterparts == and !=.

The reason for this is that == and != do type coercion which follows the rather obscure Abstract Equality Comparison Algorithm. For instance, the following statements are all considered true:

• [] == false
• [] == ![]
• 3 == "03"

If one of those occurs in an innocent-looking statement such as a == b the actual problem is very difficult to spot.

Rule Details

This rule is aimed at eliminating the type-unsafe equality operators.

Examples of incorrect code for this rule:

/*eslint eqeqeq: "error"*/

if (x == 42) { }

if ("" == text) { }

if (obj.getStuff() != undefined) { }

The --fix option on the command line automatically fixes some problems reported by this rule. A problem is only fixed if one of the operands is a typeof expression, or if both operands are literals with the same type.

Options

always

The "always" option (default) enforces the use of === and !== in every situation (except when you opt-in to more specific handling of null [see below]).

Examples of incorrect code for the "always" option:

/*eslint eqeqeq: ["error", "always"]*/

a == b
foo == true
bananas != 1
value == undefined
typeof foo == 'undefined'
'hello' != 'world'
0 == 0
true == true
foo == null

Examples of correct code for the "always" option:

/*eslint eqeqeq: ["error", "always"]*/

a === b
foo === true
bananas !== 1
value === undefined
typeof foo === 'undefined'
'hello' !== 'world'
0 === 0
true === true
foo === null

This rule optionally takes a second argument, which should be an object with the following supported properties:

• "null": Customize how this rule treats null literals. Possible values:
  • always (default) - Always use === or !==.
  • never - Never use === or !== with null.
  • ignore - Do not apply this rule to null.

smart

The "smart" option enforces the use of === and !== except for these cases:

• Comparing two literal values
• Evaluating the value of typeof
• Comparing against null

Examples of incorrect code for the "smart" option:

/*eslint eqeqeq: ["error", "smart"]*/

// comparing two variables requires ===
a == b

// only one side is a literal
foo == true
bananas != 1

// comparing to undefined requires ===
value == undefined

Examples of correct code for the "smart" option:

/*eslint eqeqeq: ["error", "smart"]*/

typeof foo == 'undefined'
'hello' != 'world'
0 == 0
true == true
foo == null

allow-null

Deprecated: Instead of using this option use "always" and pass a "null" option property with value "ignore". This will tell eslint to always enforce strict equality except when comparing with the null literal.

["error", "always", {"null": "ignore"}]

When Not To Use It

If you don't want to enforce a style for using equality operators, then it's safe to disable this rule. Source: http://eslint.org/docs/rules/

        if (urlTemplate == null)

Close

Disallow Null Comparisons (no-eq-null)

Comparing to null without a type-checking operator (== or !=), can have unintended results as the comparison will evaluate to true when comparing to not just a null, but also an undefined value.

if (foo == null) {
  bar();
}

Rule Details

The no-eq-null rule aims reduce potential bug and unwanted behavior by ensuring that comparisons to null only match null, and not also undefined. As such it will flag comparisons to null when using == and !=.

Examples of incorrect code for this rule:

/*eslint no-eq-null: "error"*/

if (foo == null) {
  bar();
}

while (qux != null) {
  baz();
}

Examples of correct code for this rule:

/*eslint no-eq-null: "error"*/

if (foo === null) {
  bar();
}

while (qux !== null) {
  baz();
}

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

;

Close

disallow unnecessary semicolons (no-extra-semi)

Typing mistakes and misunderstandings about where semicolons are required can lead to semicolons that are unnecessary. While not technically an error, extra semicolons can cause confusion when reading code.

Rule Details

This rule disallows unnecessary semicolons.

Examples of incorrect code for this rule:

/*eslint no-extra-semi: "error"*/

var x = 5;;

function foo() {
    // code
};

Examples of correct code for this rule:

/*eslint no-extra-semi: "error"*/

var x = 5;

var foo = function() {
    // code
};

When Not To Use It

If you intentionally use extra semicolons then you can disable this rule.

Related Rules

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

(function (Type) {

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/

        if (value == null && !this.isNullable)

Close

Disallow Null Comparisons (no-eq-null)

Comparing to null without a type-checking operator (== or !=), can have unintended results as the comparison will evaluate to true when comparing to not just a null, but also an undefined value.

if (foo == null) {
  bar();
}

Rule Details

The no-eq-null rule aims reduce potential bug and unwanted behavior by ensuring that comparisons to null only match null, and not also undefined. As such it will flag comparisons to null when using == and !=.

Examples of incorrect code for this rule:

/*eslint no-eq-null: "error"*/

if (foo == null) {
  bar();
}

while (qux != null) {
  baz();
}

Examples of correct code for this rule:

/*eslint no-eq-null: "error"*/

if (foo === null) {
  bar();
}

while (qux !== null) {
  baz();
}

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