var taskFile = resolve(config.tasks.directory, taskName + '.js');

Close

require let or const instead of var (no-var)

ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let and const keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes such as:

var count = people.length;
var enoughFood = count > sandwiches.length;

if (enoughFood) {
    var count = sandwiches.length; // accidentally overriding the count variable
    console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}

// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");

Rule Details

This rule is aimed at discouraging the use of var and encouraging the use of const or let instead.

Examples

Examples of incorrect code for this rule:

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

var x = "y";
var CONFIG = {};

Examples of correct code for this rule:

/*eslint no-var: "error"*/
/*eslint-env es6*/

let x = "y";
const CONFIG = {};

When Not To Use It

In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their codebase may not want to apply this rule if the cost of migrating from var to let is too costly. Source: http://eslint.org/docs/rules/

        util.log('Could not load task "' + taskName +'" from "' + taskFile + '":');

Close

require spacing around infix operators (space-infix-ops)

While formatting preferences are very personal, a number of style guides require spaces around operators, such as:

var sum = 1 + 2;

The proponents of these extra spaces believe it make the code easier to read and can more easily highlight potential errors, such as:

var sum = i+++2;

While this is valid JavaScript syntax, it is hard to determine what the author intended.

Rule Details

This rule is aimed at ensuring there are spaces around infix operators.

Options

This rule accepts a single options argument with the following defaults:

"space-infix-ops": ["error", {"int32Hint": false}]

int32Hint

Set the int32Hint option to true (default is false) to allow write a|0 without space.

var foo = bar|0; // `foo` is forced to be signed 32 bit integer

Examples of incorrect code for this rule:

/*eslint space-infix-ops: "error"*/
/*eslint-env es6*/

a+b

a+ b

a +b

a?b:c

const a={b:1};

var {a=0}=bar;

function foo(a=0) { }

Examples of correct code for this rule:

/*eslint space-infix-ops: "error"*/
/*eslint-env es6*/

a + b

a       + b

a ? b : c

const a = {b:1};

var {a = 0} = bar;

function foo(a = 0) { }

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

var gulp = require('gulp');

Close

require let or const instead of var (no-var)

ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let and const keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes such as:

var count = people.length;
var enoughFood = count > sandwiches.length;

if (enoughFood) {
    var count = sandwiches.length; // accidentally overriding the count variable
    console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}

// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");

Rule Details

This rule is aimed at discouraging the use of var and encouraging the use of const or let instead.

Examples

Examples of incorrect code for this rule:

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

var x = "y";
var CONFIG = {};

Examples of correct code for this rule:

/*eslint no-var: "error"*/
/*eslint-env es6*/

let x = "y";
const CONFIG = {};

When Not To Use It

In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their codebase may not want to apply this rule if the cost of migrating from var to let is too costly. Source: http://eslint.org/docs/rules/

    var taskName = isAliased ? taskDefinition[0] : taskDefinition;

Close

require let or const instead of var (no-var)

ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let and const keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes such as:

var count = people.length;
var enoughFood = count > sandwiches.length;

if (enoughFood) {
    var count = sandwiches.length; // accidentally overriding the count variable
    console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}

// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");

Rule Details

This rule is aimed at discouraging the use of var and encouraging the use of const or let instead.

Examples

Examples of incorrect code for this rule:

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

var x = "y";
var CONFIG = {};

Examples of correct code for this rule:

/*eslint no-var: "error"*/
/*eslint-env es6*/

let x = "y";
const CONFIG = {};

When Not To Use It

In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their codebase may not want to apply this rule if the cost of migrating from var to let is too costly. Source: http://eslint.org/docs/rules/

config.tasks.public.forEach(function(taskDefinition){

Close

Suggest using arrow functions as callbacks. (prefer-arrow-callback)

Arrow functions are suited to callbacks, because:

• this keywords in arrow functions bind to the upper scope's.
• The notation of the arrow function is shorter than function expression's.

Rule Details

This rule is aimed to flag usage of function expressions in an argument list.

The following patterns are considered problems:

/*eslint prefer-arrow-callback: "error"*/

foo(function(a) { return a; });
foo(function() { return this.a; }.bind(this));

The following patterns are not considered problems:

/*eslint prefer-arrow-callback: "error"*/
/*eslint-env es6*/

foo(a => a);
foo(function*() { yield; });

// this is not a callback.
var foo = function foo(a) { return a; };

// using `this` without `.bind(this)`.
foo(function() { return this.a; });

// recursively.
foo(function bar(n) { return n && n + bar(n - 1); });

Options

This rule takes one optional argument, an object which is an options object.

allowNamedFunctions

This is a boolean option and it is false by default. When set to true, the rule doesn't warn on named functions used as callbacks.

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

/*eslint prefer-arrow-callback: ["error", { "allowNamedFunctions": true }]*/

foo(function bar() {});

allowUnboundThis

This is a boolean option and it is true by default. When set to false, this option allows the use of this without restriction and checks for dynamically assigned this values such as when using Array.prototype.map with a context argument. Normally, the rule will flag the use of this whenever a function does not use bind() to specify the value of this constantly.

Examples of incorrect code for the { "allowUnboundThis": false } option:

/*eslint prefer-arrow-callback: ["error", { "allowUnboundThis": false }]*/
/*eslint-env es6*/

foo(function() { this.a; });

foo(function() { (() => this); });

someArray.map(function (itm) { return this.doSomething(itm); }, someObject);

When Not To Use It

This rule should not be used in ES3/5 environments.

In ES2015 (ES6) or later, if you don't want to be notified about function expressions in an argument list, you can safely disable this rule. Source: http://eslint.org/docs/rules/

var resolve = require('path').resolve;

Close

require let or const instead of var (no-var)

ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let and const keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes such as:

var count = people.length;
var enoughFood = count > sandwiches.length;

if (enoughFood) {
    var count = sandwiches.length; // accidentally overriding the count variable
    console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}

// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");

Rule Details

This rule is aimed at discouraging the use of var and encouraging the use of const or let instead.

Examples

Examples of incorrect code for this rule:

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

var x = "y";
var CONFIG = {};

Examples of correct code for this rule:

/*eslint no-var: "error"*/
/*eslint-env es6*/

let x = "y";
const CONFIG = {};

When Not To Use It

In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their codebase may not want to apply this rule if the cost of migrating from var to let is too costly. Source: http://eslint.org/docs/rules/

    } catch(err) {

Close

enforce consistent spacing before and after keywords (keyword-spacing)

Keywords are syntax elements of JavaScript, such as function and if. These identifiers have special meaning to the language and so often appear in a different color in code editors. As an important part of the language, style guides often refer to the spacing that should be used around keywords. For example, you might have a style guide that says keywords should be always surrounded by spaces, which would mean if-else statements must look like this:

if (foo) {
    // ...
} else {
    // ...
}

Of course, you could also have a style guide that disallows spaces around keywords.

Rule Details

This rule enforces consistent spacing around keywords and keyword-like tokens: as (in module declarations), async (of async functions), await (of await expressions), break, case, catch, class, const, continue, debugger, default, delete, do, else, export, extends, finally, for, from (in module declarations), function, get (of getters), if, import, in, instanceof, let, new, of (in for-of statements), return, set (of setters), static, super, switch, this, throw, try, typeof, var, void, while, with, and yield. This rule is designed carefully not to conflict with other spacing rules: it does not apply to spacing where other rules report problems.

Options

This rule has an object option:

• "before": true (default) requires at least one space before keywords
• "before": false disallows spaces before keywords
• "after": true (default) requires at least one space after keywords
• "after": false disallows spaces after keywords
• "overrides" allows overriding spacing style for specified keywords

before

Examples of incorrect code for this rule with the default { "before": true } option:

/*eslint keyword-spacing: ["error", { "before": true }]*/

if (foo) {
    //...
}else if (bar) {
    //...
}else {
    //...
}

Examples of correct code for this rule with the default { "before": true } option:

/*eslint keyword-spacing: ["error", { "before": true }]*/
/*eslint-env es6*/

if (foo) {
    //...
} else if (bar) {
    //...
} else {
    //...
}

// no conflict with `array-bracket-spacing`
let a = [this];
let b = [function() {}];

// no conflict with `arrow-spacing`
let a = ()=> this.foo;

// no conflict with `block-spacing`
{function foo() {}}

// no conflict with `comma-spacing`
let a = [100,this.foo, this.bar];

// not conflict with `computed-property-spacing`
obj[this.foo] = 0;

// no conflict with `generator-star-spacing`
function *foo() {}

// no conflict with `key-spacing`
let obj = {
    foo:function() {}
};

// no conflict with `object-curly-spacing`
let obj = {foo: this};

// no conflict with `semi-spacing`
let a = this;function foo() {}

// no conflict with `space-in-parens`
(function () {})();

// no conflict with `space-infix-ops`
if ("foo"in {foo: 0}) {}
if (10+this.foo<= this.bar) {}

// no conflict with `jsx-curly-spacing`
let a = 

Examples of incorrect code for this rule with the { "before": false } option:

/*eslint keyword-spacing: ["error", { "before": false }]*/

if (foo) {
    //...
} else if (bar) {
    //...
} else {
    //...
}

Examples of correct code for this rule with the { "before": false } option:

/*eslint keyword-spacing: ["error", { "before": false }]*/

if (foo) {
    //...
}else if (bar) {
    //...
}else {
    //...
}

after

Examples of incorrect code for this rule with the default { "after": true } option:

/*eslint keyword-spacing: ["error", { "after": true }]*/

if(foo) {
    //...
} else if(bar) {
    //...
} else{
    //...
}

Examples of correct code for this rule with the default { "after": true } option:

/*eslint keyword-spacing: ["error", { "after": true }]*/

if (foo) {
    //...
} else if (bar) {
    //...
} else {
    //...
}

// not conflict with `array-bracket-spacing`
let a = [this];

// not conflict with `arrow-spacing`
let a = ()=> this.foo;

// not conflict with `comma-spacing`
let a = [100, this.foo, this.bar];

// not conflict with `computed-property-spacing`
obj[this.foo] = 0;

// not conflict with `generator-star-spacing`
function* foo() {}

// not conflict with `key-spacing`
let obj = {
    foo:function() {}
};

// not conflict with `func-call-spacing`
class A {
    constructor() {
        super();
    }
}

// not conflict with `object-curly-spacing`
let obj = {foo: this};

// not conflict with `semi-spacing`
let a = this;function foo() {}

// not conflict with `space-before-function-paren`
function() {}

// no conflict with `space-infix-ops`
if ("foo"in{foo: 0}) {}
if (10+this.foo<= this.bar) {}

// no conflict with `space-unary-ops`
function* foo(a) {
    return yield+a;
}

// no conflict with `yield-star-spacing`
function* foo(a) {
    return yield* a;
}

// no conflict with `jsx-curly-spacing`
let a = 

Examples of incorrect code for this rule with the { "after": false } option:

/*eslint keyword-spacing: ["error", { "after": false }]*/

if (foo) {
    //...
} else if (bar) {
    //...
} else {
    //...
}

Examples of correct code for this rule with the { "after": false } option:

/*eslint keyword-spacing: ["error", { "after": false }]*/

if(foo) {
    //...
} else if(bar) {
    //...
} else{
    //...
}

overrides

Examples of correct code for this rule with the { "overrides": { "if": { "after": false }, "for": { "after": false }, "while": { "after": false } } } option:

/*eslint keyword-spacing: ["error", { "overrides": {
  "if": { "after": false },
  "for": { "after": false },
  "while": { "after": false }
} }]*/

if(foo) {
    //...
} else if(bar) {
    //...
} else {
    //...
}

for(;;);

while(true) {
  //...
}

When Not To Use It

If you don't want to enforce consistency on keyword spacing, then it's safe to disable this rule. Source: http://eslint.org/docs/rules/

var rc = require('rc');

Close

require let or const instead of var (no-var)

ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let and const keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes such as:

var count = people.length;
var enoughFood = count > sandwiches.length;

if (enoughFood) {
    var count = sandwiches.length; // accidentally overriding the count variable
    console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}

// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");

Rule Details

This rule is aimed at discouraging the use of var and encouraging the use of const or let instead.

Examples

Examples of incorrect code for this rule:

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

var x = "y";
var CONFIG = {};

Examples of correct code for this rule:

/*eslint no-var: "error"*/
/*eslint-env es6*/

let x = "y";
const CONFIG = {};

When Not To Use It

In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their codebase may not want to apply this rule if the cost of migrating from var to let is too costly. Source: http://eslint.org/docs/rules/

var task = require('./tasks/helpers/task')(gulp);

Close

require let or const instead of var (no-var)

ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let and const keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes such as:

var count = people.length;
var enoughFood = count > sandwiches.length;

if (enoughFood) {
    var count = sandwiches.length; // accidentally overriding the count variable
    console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}

// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");

Rule Details

This rule is aimed at discouraging the use of var and encouraging the use of const or let instead.

Examples

Examples of incorrect code for this rule:

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

var x = "y";
var CONFIG = {};

Examples of correct code for this rule:

/*eslint no-var: "error"*/
/*eslint-env es6*/

let x = "y";
const CONFIG = {};

When Not To Use It

In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their codebase may not want to apply this rule if the cost of migrating from var to let is too costly. Source: http://eslint.org/docs/rules/

    var isAliased = Array.isArray(taskDefinition);

Close

require let or const instead of var (no-var)

ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let and const keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes such as:

var count = people.length;
var enoughFood = count > sandwiches.length;

if (enoughFood) {
    var count = sandwiches.length; // accidentally overriding the count variable
    console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}

// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");

Rule Details

This rule is aimed at discouraging the use of var and encouraging the use of const or let instead.

Examples

Examples of incorrect code for this rule:

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

var x = "y";
var CONFIG = {};

Examples of correct code for this rule:

/*eslint no-var: "error"*/
/*eslint-env es6*/

let x = "y";
const CONFIG = {};

When Not To Use It

In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their codebase may not want to apply this rule if the cost of migrating from var to let is too costly. Source: http://eslint.org/docs/rules/

    var taskFactory, taskFunction;

Close

require let or const instead of var (no-var)

ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let and const keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes such as:

var count = people.length;
var enoughFood = count > sandwiches.length;

if (enoughFood) {
    var count = sandwiches.length; // accidentally overriding the count variable
    console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}

// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");

Rule Details

This rule is aimed at discouraging the use of var and encouraging the use of const or let instead.

Examples

Examples of incorrect code for this rule:

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

var x = "y";
var CONFIG = {};

Examples of correct code for this rule:

/*eslint no-var: "error"*/
/*eslint-env es6*/

let x = "y";
const CONFIG = {};

When Not To Use It

In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their codebase may not want to apply this rule if the cost of migrating from var to let is too costly. Source: http://eslint.org/docs/rules/

    } catch(err) {

Close

enforce consistent spacing before and after keywords (keyword-spacing)

Keywords are syntax elements of JavaScript, such as function and if. These identifiers have special meaning to the language and so often appear in a different color in code editors. As an important part of the language, style guides often refer to the spacing that should be used around keywords. For example, you might have a style guide that says keywords should be always surrounded by spaces, which would mean if-else statements must look like this:

if (foo) {
    // ...
} else {
    // ...
}

Of course, you could also have a style guide that disallows spaces around keywords.

Rule Details

This rule enforces consistent spacing around keywords and keyword-like tokens: as (in module declarations), async (of async functions), await (of await expressions), break, case, catch, class, const, continue, debugger, default, delete, do, else, export, extends, finally, for, from (in module declarations), function, get (of getters), if, import, in, instanceof, let, new, of (in for-of statements), return, set (of setters), static, super, switch, this, throw, try, typeof, var, void, while, with, and yield. This rule is designed carefully not to conflict with other spacing rules: it does not apply to spacing where other rules report problems.

Options

This rule has an object option:

• "before": true (default) requires at least one space before keywords
• "before": false disallows spaces before keywords
• "after": true (default) requires at least one space after keywords
• "after": false disallows spaces after keywords
• "overrides" allows overriding spacing style for specified keywords

before

Examples of incorrect code for this rule with the default { "before": true } option:

/*eslint keyword-spacing: ["error", { "before": true }]*/

if (foo) {
    //...
}else if (bar) {
    //...
}else {
    //...
}

Examples of correct code for this rule with the default { "before": true } option:

/*eslint keyword-spacing: ["error", { "before": true }]*/
/*eslint-env es6*/

if (foo) {
    //...
} else if (bar) {
    //...
} else {
    //...
}

// no conflict with `array-bracket-spacing`
let a = [this];
let b = [function() {}];

// no conflict with `arrow-spacing`
let a = ()=> this.foo;

// no conflict with `block-spacing`
{function foo() {}}

// no conflict with `comma-spacing`
let a = [100,this.foo, this.bar];

// not conflict with `computed-property-spacing`
obj[this.foo] = 0;

// no conflict with `generator-star-spacing`
function *foo() {}

// no conflict with `key-spacing`
let obj = {
    foo:function() {}
};

// no conflict with `object-curly-spacing`
let obj = {foo: this};

// no conflict with `semi-spacing`
let a = this;function foo() {}

// no conflict with `space-in-parens`
(function () {})();

// no conflict with `space-infix-ops`
if ("foo"in {foo: 0}) {}
if (10+this.foo<= this.bar) {}

// no conflict with `jsx-curly-spacing`
let a = 

Examples of incorrect code for this rule with the { "before": false } option:

/*eslint keyword-spacing: ["error", { "before": false }]*/

if (foo) {
    //...
} else if (bar) {
    //...
} else {
    //...
}

Examples of correct code for this rule with the { "before": false } option:

/*eslint keyword-spacing: ["error", { "before": false }]*/

if (foo) {
    //...
}else if (bar) {
    //...
}else {
    //...
}

after

Examples of incorrect code for this rule with the default { "after": true } option:

/*eslint keyword-spacing: ["error", { "after": true }]*/

if(foo) {
    //...
} else if(bar) {
    //...
} else{
    //...
}

Examples of correct code for this rule with the default { "after": true } option:

/*eslint keyword-spacing: ["error", { "after": true }]*/

if (foo) {
    //...
} else if (bar) {
    //...
} else {
    //...
}

// not conflict with `array-bracket-spacing`
let a = [this];

// not conflict with `arrow-spacing`
let a = ()=> this.foo;

// not conflict with `comma-spacing`
let a = [100, this.foo, this.bar];

// not conflict with `computed-property-spacing`
obj[this.foo] = 0;

// not conflict with `generator-star-spacing`
function* foo() {}

// not conflict with `key-spacing`
let obj = {
    foo:function() {}
};

// not conflict with `func-call-spacing`
class A {
    constructor() {
        super();
    }
}

// not conflict with `object-curly-spacing`
let obj = {foo: this};

// not conflict with `semi-spacing`
let a = this;function foo() {}

// not conflict with `space-before-function-paren`
function() {}

// no conflict with `space-infix-ops`
if ("foo"in{foo: 0}) {}
if (10+this.foo<= this.bar) {}

// no conflict with `space-unary-ops`
function* foo(a) {
    return yield+a;
}

// no conflict with `yield-star-spacing`
function* foo(a) {
    return yield* a;
}

// no conflict with `jsx-curly-spacing`
let a = 

Examples of incorrect code for this rule with the { "after": false } option:

/*eslint keyword-spacing: ["error", { "after": false }]*/

if (foo) {
    //...
} else if (bar) {
    //...
} else {
    //...
}

Examples of correct code for this rule with the { "after": false } option:

/*eslint keyword-spacing: ["error", { "after": false }]*/

if(foo) {
    //...
} else if(bar) {
    //...
} else{
    //...
}

overrides

Examples of correct code for this rule with the { "overrides": { "if": { "after": false }, "for": { "after": false }, "while": { "after": false } } } option:

/*eslint keyword-spacing: ["error", { "overrides": {
  "if": { "after": false },
  "for": { "after": false },
  "while": { "after": false }
} }]*/

if(foo) {
    //...
} else if(bar) {
    //...
} else {
    //...
}

for(;;);

while(true) {
  //...
}

When Not To Use It

If you don't want to enforce consistency on keyword spacing, then it's safe to disable this rule. Source: http://eslint.org/docs/rules/

    var taskAliases = isAliased ? (taskDefinition[1] || []).concat([taskName]) : [taskName];

Close

require let or const instead of var (no-var)

ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let and const keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes such as:

var count = people.length;
var enoughFood = count > sandwiches.length;

if (enoughFood) {
    var count = sandwiches.length; // accidentally overriding the count variable
    console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}

// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");

Rule Details

This rule is aimed at discouraging the use of var and encouraging the use of const or let instead.

Examples

Examples of incorrect code for this rule:

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

var x = "y";
var CONFIG = {};

Examples of correct code for this rule:

/*eslint no-var: "error"*/
/*eslint-env es6*/

let x = "y";
const CONFIG = {};

When Not To Use It

In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their codebase may not want to apply this rule if the cost of migrating from var to let is too costly. Source: http://eslint.org/docs/rules/

config.tasks.public.forEach(function(taskDefinition){

Close

Require or disallow a space before function parenthesis (space-before-function-paren)

When formatting a function, whitespace is allowed between the function name or function keyword and the opening paren. Named functions also require a space between the function keyword and the function name, but anonymous functions require no whitespace. For example:

function withoutSpace(x) {
    // ...
}

function withSpace (x) {
    // ...
}

var anonymousWithoutSpace = function() {};

var anonymousWithSpace = function () {};

Style guides may require a space after the function keyword for anonymous functions, while others specify no whitespace. Similarly, the space after a function name may or may not be required.

Rule Details

This rule aims to enforce consistent spacing before function parentheses and as such, will warn whenever whitespace doesn't match the preferences specified.

Options

This rule has a string option or an object option:

{
    "space-before-function-paren": ["error", "always"],
    // or
    "space-before-function-paren": ["error", {
        "anonymous": "always",
        "named": "always",
        "asyncArrow": "ignore"
    }],
}

• always (default) requires a space followed by the ( of arguments.
• never disallows any space followed by the ( of arguments.

The string option does not check async arrow function expressions for backward compatibility.

You can also use a separate option for each type of function. Each of the following options can be set to "always", "never", or "ignore". Default is "always" basically.

• anonymous is for anonymous function expressions (e.g. function () {}).
• named is for named function expressions (e.g. function foo () {}).
• asyncArrow is for async arrow function expressions (e.g. async () => {}). asyncArrow is set to "ignore" by default for backwards compatibility.

"always"

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

/*eslint space-before-function-paren: "error"*/
/*eslint-env es6*/

function foo() {
    // ...
}

var bar = function() {
    // ...
};

var bar = function foo() {
    // ...
};

class Foo {
    constructor() {
        // ...
    }
}

var foo = {
    bar() {
        // ...
    }
};

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

/*eslint space-before-function-paren: "error"*/
/*eslint-env es6*/

function foo () {
    // ...
}

var bar = function () {
    // ...
};

var bar = function foo () {
    // ...
};

class Foo {
    constructor () {
        // ...
    }
}

var foo = {
    bar () {
        // ...
    }
};

// async arrow function expressions are ignored by default.
var foo = async () => 1
var foo = async() => 1

"never"

Examples of incorrect code for this rule with the "never" option:

/*eslint space-before-function-paren: ["error", "never"]*/
/*eslint-env es6*/

function foo () {
    // ...
}

var bar = function () {
    // ...
};

var bar = function foo () {
    // ...
};

class Foo {
    constructor () {
        // ...
    }
}

var foo = {
    bar () {
        // ...
    }
};

Examples of correct code for this rule with the "never" option:

/*eslint space-before-function-paren: ["error", "never"]*/
/*eslint-env es6*/

function foo() {
    // ...
}

var bar = function() {
    // ...
};

var bar = function foo() {
    // ...
};

class Foo {
    constructor() {
        // ...
    }
}

var foo = {
    bar() {
        // ...
    }
};

// async arrow function expressions are ignored by default.
var foo = async () => 1
var foo = async() => 1

{"anonymous": "always", "named": "never", "asyncArrow": "always"}

Examples of incorrect code for this rule with the {"anonymous": "always", "named": "never", "asyncArrow": "always"} option:

/*eslint space-before-function-paren: ["error", {"anonymous": "always", "named": "never", "asyncArrow": "always"}]*/
/*eslint-env es6*/

function foo () {
    // ...
}

var bar = function() {
    // ...
};

class Foo {
    constructor () {
        // ...
    }
}

var foo = {
    bar () {
        // ...
    }
};

var foo = async(a) => await a

Examples of correct code for this rule with the {"anonymous": "always", "named": "never", "asyncArrow": "always"} option:

/*eslint space-before-function-paren: ["error", {"anonymous": "always", "named": "never", "asyncArrow": "always"}]*/
/*eslint-env es6*/

function foo() {
    // ...
}

var bar = function () {
    // ...
};

class Foo {
    constructor() {
        // ...
    }
}

var foo = {
    bar() {
        // ...
    }
};

var foo = async (a) => await a

{"anonymous": "never", "named": "always"}

Examples of incorrect code for this rule with the {"anonymous": "never", "named": "always"} option:

/*eslint space-before-function-paren: ["error", { "anonymous": "never", "named": "always" }]*/
/*eslint-env es6*/

function foo() {
    // ...
}

var bar = function () {
    // ...
};

class Foo {
    constructor() {
        // ...
    }
}

var foo = {
    bar() {
        // ...
    }
};

Examples of correct code for this rule with the {"anonymous": "never", "named": "always"} option:

/*eslint space-before-function-paren: ["error", { "anonymous": "never", "named": "always" }]*/
/*eslint-env es6*/

function foo () {
    // ...
}

var bar = function() {
    // ...
};

class Foo {
    constructor () {
        // ...
    }
}

var foo = {
    bar () {
        // ...
    }
};

{"anonymous": "ignore", "named": "always"}

Examples of incorrect code for this rule with the {"anonymous": "ignore", "named": "always"} option:

/*eslint space-before-function-paren: ["error", { "anonymous": "ignore", "named": "always" }]*/
/*eslint-env es6*/

function foo() {
    // ...
}

class Foo {
    constructor() {
        // ...
    }
}

var foo = {
    bar() {
        // ...
    }
};

Examples of correct code for this rule with the {"anonymous": "ignore", "named": "always"} option:

/*eslint space-before-function-paren: ["error", { "anonymous": "ignore", "named": "always" }]*/
/*eslint-env es6*/

var bar = function() {
    // ...
};

var bar = function () {
    // ...
};

function foo () {
    // ...
}

class Foo {
    constructor () {
        // ...
    }
}

var foo = {
    bar () {
        // ...
    }
};

When Not To Use It

You can turn this rule off if you are not concerned with the consistency of spacing before function parenthesis.

Related Rules

• [space-after-keywords](space-after-keywords.md)
• [space-return-throw-case](space-return-throw-case.md) Source: http://eslint.org/docs/rules/

        util.log('Could not initialize task function "' + taskName +'" from "' + taskFile + '":');

Close

require spacing around infix operators (space-infix-ops)

While formatting preferences are very personal, a number of style guides require spaces around operators, such as:

var sum = 1 + 2;

The proponents of these extra spaces believe it make the code easier to read and can more easily highlight potential errors, such as:

var sum = i+++2;

While this is valid JavaScript syntax, it is hard to determine what the author intended.

Rule Details

This rule is aimed at ensuring there are spaces around infix operators.

Options

This rule accepts a single options argument with the following defaults:

"space-infix-ops": ["error", {"int32Hint": false}]

int32Hint

Set the int32Hint option to true (default is false) to allow write a|0 without space.

var foo = bar|0; // `foo` is forced to be signed 32 bit integer

Examples of incorrect code for this rule:

/*eslint space-infix-ops: "error"*/
/*eslint-env es6*/

a+b

a+ b

a +b

a?b:c

const a={b:1};

var {a=0}=bar;

function foo(a=0) { }

Examples of correct code for this rule:

/*eslint space-infix-ops: "error"*/
/*eslint-env es6*/

a + b

a       + b

a ? b : c

const a = {b:1};

var {a = 0} = bar;

function foo(a = 0) { }

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

var util = require('gulp-util');

Close

require let or const instead of var (no-var)

ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let and const keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes such as:

var count = people.length;
var enoughFood = count > sandwiches.length;

if (enoughFood) {
    var count = sandwiches.length; // accidentally overriding the count variable
    console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}

// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");

Rule Details

This rule is aimed at discouraging the use of var and encouraging the use of const or let instead.

Examples

Examples of incorrect code for this rule:

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

var x = "y";
var CONFIG = {};

Examples of correct code for this rule:

/*eslint no-var: "error"*/
/*eslint-env es6*/

let x = "y";
const CONFIG = {};

When Not To Use It

In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their codebase may not want to apply this rule if the cost of migrating from var to let is too costly. Source: http://eslint.org/docs/rules/

var minimist = require('minimist');

Close

require let or const instead of var (no-var)

ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let and const keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes such as:

var count = people.length;
var enoughFood = count > sandwiches.length;

if (enoughFood) {
    var count = sandwiches.length; // accidentally overriding the count variable
    console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}

// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");

Rule Details

This rule is aimed at discouraging the use of var and encouraging the use of const or let instead.

Examples

Examples of incorrect code for this rule:

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

var x = "y";
var CONFIG = {};

Examples of correct code for this rule:

/*eslint no-var: "error"*/
/*eslint-env es6*/

let x = "y";
const CONFIG = {};

When Not To Use It

In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their codebase may not want to apply this rule if the cost of migrating from var to let is too costly. Source: http://eslint.org/docs/rules/

var config = rc('gulp', {

Close

require let or const instead of var (no-var)

ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let and const keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes such as:

var count = people.length;
var enoughFood = count > sandwiches.length;

if (enoughFood) {
    var count = sandwiches.length; // accidentally overriding the count variable
    console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}

// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");

Rule Details

This rule is aimed at discouraging the use of var and encouraging the use of const or let instead.

Examples

Examples of incorrect code for this rule:

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

var x = "y";
var CONFIG = {};

Examples of correct code for this rule:

/*eslint no-var: "error"*/
/*eslint-env es6*/

let x = "y";
const CONFIG = {};

When Not To Use It

In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their codebase may not want to apply this rule if the cost of migrating from var to let is too costly. Source: http://eslint.org/docs/rules/

    var taskOptions = isAliased ? (taskDefinition[2] || {}) : {};

Close

require let or const instead of var (no-var)

ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let and const keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes such as:

var count = people.length;
var enoughFood = count > sandwiches.length;

if (enoughFood) {
    var count = sandwiches.length; // accidentally overriding the count variable
    console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}

// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");

Rule Details

This rule is aimed at discouraging the use of var and encouraging the use of const or let instead.

Examples

Examples of incorrect code for this rule:

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

var x = "y";
var CONFIG = {};

Examples of correct code for this rule:

/*eslint no-var: "error"*/
/*eslint-env es6*/

let x = "y";
const CONFIG = {};

When Not To Use It

In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their codebase may not want to apply this rule if the cost of migrating from var to let is too costly. Source: http://eslint.org/docs/rules/

var cliOptions = minimist(process.argv.slice(2));

Close

require let or const instead of var (no-var)

ECMAScript 6 allows programmers to create variables with block scope instead of function scope using the let and const keywords. Block scope is common in many other programming languages and helps programmers avoid mistakes such as:

var count = people.length;
var enoughFood = count > sandwiches.length;

if (enoughFood) {
    var count = sandwiches.length; // accidentally overriding the count variable
    console.log("We have " + count + " sandwiches for everyone. Plenty for all!");
}

// our count variable is no longer accurate
console.log("We have " + count + " people and " + sandwiches.length + " sandwiches!");

Rule Details

This rule is aimed at discouraging the use of var and encouraging the use of const or let instead.

Examples

Examples of incorrect code for this rule:

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

var x = "y";
var CONFIG = {};

Examples of correct code for this rule:

/*eslint no-var: "error"*/
/*eslint-env es6*/

let x = "y";
const CONFIG = {};

When Not To Use It

In addition to non-ES6 environments, existing JavaScript projects that are beginning to introduce ES6 into their codebase may not want to apply this rule if the cost of migrating from var to let is too costly. Source: http://eslint.org/docs/rules/

config.tasks.public.forEach(function(taskDefinition){

Close

Require Or Disallow Space Before Blocks (space-before-blocks)

Consistency is an important part of any style guide. While it is a personal preference where to put the opening brace of blocks, it should be consistent across a whole project. Having an inconsistent style distracts the reader from seeing the important parts of the code.

Rule Details

This rule will enforce consistency of spacing before blocks. It is only applied on blocks that don’t begin on a new line.

• This rule ignores spacing which is between => and a block. The spacing is handled by the arrow-spacing rule.
• This rule ignores spacing which is between a keyword and a block. The spacing is handled by the keyword-spacing rule.

Options

This rule takes one argument. If it is "always" then blocks must always have at least one preceding space. If "never" then all blocks should never have any preceding space. If different spacing is desired for function blocks, keyword blocks and classes, an optional configuration object can be passed as the rule argument to configure the cases separately.

( e.g. { "functions": "never", "keywords": "always", "classes": "always" } )

The default is "always".

"always"

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

/*eslint space-before-blocks: "error"*/

if (a){
    b();
}

function a(){}

for (;;){
    b();
}

try {} catch(a){}

class Foo{
  constructor(){}
}

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

/*eslint space-before-blocks: "error"*/

if (a) {
    b();
}

if (a) {
    b();
} else{ /*no error. this is checked by `keyword-spacing` rule.*/
    c();
}


function a() {}

for (;;) {
    b();
}

try {} catch(a) {}

"never"

Examples of incorrect code for this rule with the "never" option:

/*eslint space-before-blocks: ["error", "never"]*/

if (a) {
    b();
}

function a() {}

for (;;) {
    b();
}

try {} catch(a) {}

Examples of correct code for this rule with the "never" option:

/*eslint space-before-blocks: ["error", "never"]*/

if (a){
    b();
}

function a(){}

for (;;){
    b();
}

try{} catch(a){}

class Foo{
  constructor(){}
}

Examples of incorrect code for this rule when configured { "functions": "never", "keywords": "always", "classes": "never" }:

/*eslint space-before-blocks: ["error", { "functions": "never", "keywords": "always", "classes": "never" }]*/
/*eslint-env es6*/

function a() {}

try {} catch(a){}

class Foo{
  constructor() {}
}

Examples of correct code for this rule when configured { "functions": "never", "keywords": "always", "classes": "never" }:

/*eslint space-before-blocks: ["error", { "functions": "never", "keywords": "always", "classes": "never" }]*/
/*eslint-env es6*/

for (;;) {
  // ...
}

describe(function(){
  // ...
});

class Foo {
  constructor(){}
}

Examples of incorrect code for this rule when configured { "functions": "always", "keywords": "never", "classes": "never" }:

/*eslint space-before-blocks: ["error", { "functions": "always", "keywords": "never", "classes": "never" }]*/
/*eslint-env es6*/

function a(){}

try {} catch(a) {}

class Foo {
  constructor(){}
}

Examples of correct code for this rule when configured { "functions": "always", "keywords": "never", "classes": "never" }:

/*eslint space-before-blocks: ["error", { "functions": "always", "keywords": "never", "classes": "never" }]*/
/*eslint-env es6*/

if (a){
  b();
}

var a = function() {}

class Foo{
  constructor() {}
}

Examples of incorrect code for this rule when configured { "functions": "never", "keywords": "never", "classes": "always" }:

/*eslint space-before-blocks: ["error", { "functions": "never", "keywords": "never", "classes": "always" }]*/
/*eslint-env es6*/

class Foo{
  constructor(){}
}

Examples of correct code for this rule when configured { "functions": "never", "keywords": "never", "classes": "always" }:

/*eslint space-before-blocks: ["error", { "functions": "never", "keywords": "never", "classes": "always" }]*/
/*eslint-env es6*/

class Foo {
  constructor(){}
}

When Not To Use It

You can turn this rule off if you are not concerned with the consistency of spacing before blocks.

Related Rules

• [keyword-spacing](keyword-spacing.md)
• [arrow-spacing](arrow-spacing.md)
• [brace-style](brace-style.md) Source: http://eslint.org/docs/rules/

    var taskFactory, taskFunction;

Close

enforce variables to be declared either together or separately in functions (one-var)

Variables can be declared at any point in JavaScript code using var, let, or const. There are many styles and preferences related to the declaration of variables, and one of those is deciding on how many variable declarations should be allowed in a single function.

There are two schools of thought in this regard:

1. There should be just one variable declaration for all variables in the function. That declaration typically appears at the top of the function.
2. You should use one variable declaration for each variable you want to define.

For instance:

// one variable declaration per function
function foo() {
    var bar, baz;
}

// multiple variable declarations per function
function foo() {
    var bar;
    var baz;
}

The single-declaration school of thought is based in pre-ECMAScript 6 behaviors, where there was no such thing as block scope, only function scope. Since all var statements are hoisted to the top of the function anyway, some believe that declaring all variables in a single declaration at the top of the function removes confusion around scoping rules.

Rule Details

This rule enforces variables to be declared either together or separately per function ( for var) or block (for let and const) scope.

Options

This rule has one option, which can be a string option or an object option.

String option:

• "always" (default) requires one variable declaration per scope
• "never" requires multiple variable declarations per scope

Object option:

• "var": "always" requires one var declaration per function
• "var": "never" requires multiple var declarations per function
• "let": "always" requires one let declaration per block
• "let": "never" requires multiple let declarations per block
• "const": "always" requires one const declaration per block
• "const": "never" requires multiple const declarations per block

Alternate object option:

• "initialized": "always" requires one variable declaration for initialized variables per scope
• "initialized": "never" requires multiple variable declarations for initialized variables per scope
• "uninitialized": "always" requires one variable declaration for uninitialized variables per scope
• "uninitialized": "never" requires multiple variable declarations for uninitialized variables per scope

always

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

/*eslint one-var: ["error", "always"]*/
/*eslint-env es6*/

function foo() {
    var bar;
    var baz;
    let qux;
    let norf;
}

function foo(){
    const bar = false;
    const baz = true;
    let qux;
    let norf;
}

function foo() {
    var bar;

    if (baz) {
        var qux = true;
    }
}

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

/*eslint one-var: ["error", "always"]*/
/*eslint-env es6*/

function foo() {
    var bar,
        baz;
    let qux,
        norf;
}

function foo(){
    const bar = true,
        baz = false;
    let qux,
        norf;
}

function foo() {
    var bar,
        qux;

    if (baz) {
        qux = true;
    }
}

function foo(){
    let bar;

    if (baz) {
        let qux;
    }
}

never

Examples of incorrect code for this rule with the "never" option:

/*eslint one-var: ["error", "never"]*/
/*eslint-env es6*/

function foo() {
    var bar,
        baz;
    const bar = true,
        baz = false;
}

function foo() {
    var bar,
        qux;

    if (baz) {
        qux = true;
    }
}

function foo(){
    let bar = true,
        baz = false;
}

Examples of correct code for this rule with the "never" option:

/*eslint one-var: ["error", "never"]*/
/*eslint-env es6*/

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

function foo() {
    var bar;

    if (baz) {
        var qux = true;
    }
}

function foo() {
    let bar;

    if (baz) {
        let qux = true;
    }
}

var, let, and const

Examples of incorrect code for this rule with the { var: "always", let: "never", const: "never" } option:

/*eslint one-var: ["error", { var: "always", let: "never", const: "never" }]*/
/*eslint-env es6*/

function foo() {
    var bar;
    var baz;
    let qux,
        norf;
}

function foo() {
    const bar = 1,
          baz = 2;
    let qux,
        norf;
}

Examples of correct code for this rule with the { var: "always", let: "never", const: "never" } option:

/*eslint one-var: ["error", { var: "always", let: "never", const: "never" }]*/
/*eslint-env es6*/

function foo() {
    var bar,
        baz;
    let qux;
    let norf;
}

function foo() {
    const bar = 1;
    const baz = 2;
    let qux;
    let norf;
}

Examples of incorrect code for this rule with the { var: "never" } option:

/*eslint one-var: ["error", { var: "never" }]*/
/*eslint-env es6*/

function foo() {
    var bar,
        baz;
}

Examples of correct code for this rule with the { var: "never" } option:

/*eslint one-var: ["error", { var: "never" }]*/
/*eslint-env es6*/

function foo() {
    var bar,
        baz;
    const bar = 1; // `const` and `let` declarations are ignored if they are not specified
    const baz = 2;
    let qux;
    let norf;
}

initialized and uninitialized

Examples of incorrect code for this rule with the { "initialized": "always", "uninitialized": "never" } option:

/*eslint one-var: ["error", { "initialized": "always", "uninitialized": "never" }]*/
/*eslint-env es6*/

function foo() {
    var a, b, c;
    var foo = true;
    var bar = false;
}

Examples of correct code for this rule with the { "initialized": "always", "uninitialized": "never" } option:

/*eslint one-var: ["error", { "initialized": "always", "uninitialized": "never" }]*/

function foo() {
    var a;
    var b;
    var c;
    var foo = true,
        bar = false;
}

for (let z of foo) {
    doSomething(z);
}

let z;
for (z of foo) {
    doSomething(z);
}

Examples of incorrect code for this rule with the { "initialized": "never" } option:

/*eslint one-var: ["error", { "initialized": "never" }]*/
/*eslint-env es6*/

function foo() {
    var foo = true,
        bar = false;
}

Examples of correct code for this rule with the { "initialized": "never" } option:

/*eslint one-var: ["error", { initialized: "never" }]*/

function foo() {
    var foo = true;
    var bar = false;
    var a, b, c; // Uninitialized variables are ignored
}

Compatibility

• JSHint: This rule maps to the onevar JSHint rule, but allows let and const to be configured separately.
• JSCS: This rule roughly maps to disallowMultipleVarDecl Source: http://eslint.org/docs/rules/

        util.log('Could not load task "' + taskName +'" from "' + taskFile + '", does not export factory function.');

Close

require spacing around infix operators (space-infix-ops)

While formatting preferences are very personal, a number of style guides require spaces around operators, such as:

var sum = 1 + 2;

The proponents of these extra spaces believe it make the code easier to read and can more easily highlight potential errors, such as:

var sum = i+++2;

While this is valid JavaScript syntax, it is hard to determine what the author intended.

Rule Details

This rule is aimed at ensuring there are spaces around infix operators.

Options

This rule accepts a single options argument with the following defaults:

"space-infix-ops": ["error", {"int32Hint": false}]

int32Hint

Set the int32Hint option to true (default is false) to allow write a|0 without space.

var foo = bar|0; // `foo` is forced to be signed 32 bit integer

Examples of incorrect code for this rule:

/*eslint space-infix-ops: "error"*/
/*eslint-env es6*/

a+b

a+ b

a +b

a?b:c

const a={b:1};

var {a=0}=bar;

function foo(a=0) { }

Examples of correct code for this rule:

/*eslint space-infix-ops: "error"*/
/*eslint-env es6*/

a + b

a       + b

a ? b : c

const a = {b:1};

var {a = 0} = bar;

function foo(a = 0) { }

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

        util.log(err.stack);

Close

Disallow Undeclared Variables (no-undef)

This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var keyword in a for loop initializer).

Rule Details

Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/ comment.

Examples of incorrect code for this rule:

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

var a = someFunction();
b = 10;

Examples of correct code for this rule with global declaration:

/*global someFunction b:true*/
/*eslint no-undef: "error"*/

var a = someFunction();
b = 10;

The b:true syntax in /*global */ indicates that assignment to b is correct.

Examples of incorrect code for this rule with global declaration:

/*global b*/
/*eslint no-undef: "error"*/

b = 10;

By default, variables declared in /*global */ are read-only, therefore assignment is incorrect.

Options

• typeof set to true will warn for variables used inside typeof check (Default false).

typeof

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

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

if (typeof UndefinedIdentifier === "undefined") {
    // do something ...
}

You can use this option if you want to prevent typeof check on a variable which has not been declared.

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

/*eslint no-undef: ["error", { "typeof": true }] */

if(typeof a === "string"){}

Examples of correct code for the { "typeof": true } option with global declaration:

/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */

if(typeof a === "string"){}

Environments

For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in Specifying Environments. A few examples are given below.

browser

Examples of correct code for this rule with browser environment:

/*eslint no-undef: "error"*/
/*eslint-env browser*/

setTimeout(function() {
    alert("Hello");
});

node

Examples of correct code for this rule with node environment:

/*eslint no-undef: "error"*/
/*eslint-env node*/

var fs = require("fs");
module.exports = function() {
    console.log(fs);
};

When Not To Use It

If explicit declaration of global variables is not to your taste.

Compatibility

This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/

    try {
        taskFactory = require(taskFile);
    } catch(err) {
        util.log('Could not load task "' + taskName +'" from "' + taskFile + '":');
        util.log(err);

Close

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 62.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

    try {
        taskFunction = taskFactory(gulp, config.paths, taskOptions, cliOptions);
    } catch(err) {
        util.log('Could not initialize task function "' + taskName +'" from "' + taskFile + '":');
        util.log(err);

Close

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 62.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76