转自： https://github.com/airbnb/javascript/blob/master/README.md

Airbnb JavaScript Style Guide() {

A mostly reasonable approach to JavaScript

Other Style Guides

ES5
React
CSS & Sass
Ruby

Types
References
Objects
Arrays
Destructuring
Strings
Functions
Arrow Functions
Constructors
Modules
Iterators and Generators
Properties
Variables
Hoisting
Comparison Operators & Equality
Blocks
Comments
Whitespace
Commas
Semicolons
Type Casting & Coercion
Naming Conventions
Accessors
Events
jQuery
ECMAScript 5 Compatibility
ECMAScript 6 Styles
Testing
Performance
Resources
In the Wild
Translation
The JavaScript Style Guide Guide
Chat With Us About JavaScript
Contributors
License

Types

1.1 Primitives: When you access a primitive type you work directly on its value.
- string
- number
- boolean
- null
- undefined
```
const foo = 1;
let bar = foo; bar = 9; console.log(foo, bar); // => 1, 9
```
1.2 Complex: When you access a complex type you work on a reference to its value.
- object
- array
- function
```
const foo = [1, 2];
const bar = foo; bar[0] = 9; console.log(foo[0], bar[0]); // => 9, 9
```

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References

2.1 Use const for all of your references; avoid using var.

Why? This ensures that you can't reassign your references (mutation), which can lead to bugs and difficult to comprehend code.
```
  // badvar a = 1;var b = 2; // good const a = 1; const b = 2;
```
2.2 If you must mutate references, use let instead of var.

Why? let is block-scoped rather than function-scoped like var.
```
  // badvar count = 1;if (true) { count += 1; } // good, use the let. let count = 1; if (true) { count += 1; }
```

2.3 Note that both let and const are block-scoped.

// const and let only exist in the blocks they are defined in.
{let a = 1;const b = 1; } console.log(a); // ReferenceError console.log(b); // ReferenceError

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Objects

3.1 Use the literal syntax for object creation.

// bad
const item = new Object(); // good const item = {};

3.2 If your code will be executed in browsers in script context, don't use reserved words as keys. It won't work in IE8. More info. It’s OK to use them in ES6 modules and server-side code.
```
// bad
const superman = {default: { clark: 'kent' }, private: true, }; // good const superman = { defaults: { clark: 'kent' }, hidden: true, };
```

3.3 Use readable synonyms in place of reserved words.

// bad
const superman = {class: 'alien', }; // bad const superman = { klass: 'alien', }; // good const superman = { type: 'alien', };

3.4 Use computed property names when creating objects with dynamic property names.

Why? They allow you to define all the properties of an object in one place.

  function getKey(k) {return `a key named ${k}`; } // bad const obj = { id: 5, name: 'San Francisco', }; obj[getKey('enabled')] = true; // good const obj = { id: 5, name: 'San Francisco', [getKey('enabled')]: true, };

3.5 Use object method shorthand.

// bad
const atom = {value: 1, addValue: function (value) { return atom.value + value; }, }; // good const atom = { value: 1, addValue(value) { return atom.value + value; }, };

3.6 Use property value shorthand.

Why? It is shorter to write and descriptive.

  const lukeSkywalker = 'Luke Skywalker'; // bad const obj = { lukeSkywalker: lukeSkywalker, }; // good const obj = { lukeSkywalker, };

3.7 Group your shorthand properties at the beginning of your object declaration.

Why? It's easier to tell which properties are using the shorthand.

  const anakinSkywalker = 'Anakin Skywalker'; const lukeSkywalker = 'Luke Skywalker'; // bad const obj = { episodeOne: 1, twoJediWalkIntoACantina: 2, lukeSkywalker, episodeThree: 3, mayTheFourth: 4, anakinSkywalker, }; // good const obj = { lukeSkywalker, anakinSkywalker, episodeOne: 1, twoJediWalkIntoACantina: 2, episodeThree: 3, mayTheFourth: 4, };

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Arrays

4.1 Use the literal syntax for array creation.

// bad
const items = new Array(); // good const items = [];

4.2 Use Array#push instead of direct assignment to add items to an array.

const someStack = [];// bad
someStack[someStack.length] = 'abracadabra'; // good someStack.push('abracadabra');

4.3 Use array spreads ... to copy arrays.

// bad
const len = items.length;
const itemsCopy = []; let i; for (i = 0; i < len; i++) { itemsCopy[i] = items[i]; } // good const itemsCopy = [...items];

4.4 To convert an array-like object to an array, use Array#from.

const foo = document.querySelectorAll('.foo'); const nodes = Array.from(foo);

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Destructuring

5.1 Use object destructuring when accessing and using multiple properties of an object.

Why? Destructuring saves you from creating temporary references for those properties.

  // badfunction getFullName(user) {const firstName = user.firstName; const lastName = user.lastName; return `${firstName} ${lastName}`; } // good function getFullName(obj) { const { firstName, lastName } = obj; return `${firstName} ${lastName}`; } // best function getFullName({ firstName, lastName }) { return `${firstName} ${lastName}`; }

5.2 Use array destructuring.

const arr = [1, 2, 3, 4]; // bad const first = arr[0]; const second = arr[1]; // good const [first, second] = arr;

5.3 Use object destructuring for multiple return values, not array destructuring.

Why? You can add new properties over time or change the order of things without breaking call sites.

  // badfunction processInput(input) {// then a miracle occursreturn [left, right, top, bottom]; } // the caller needs to think about the order of return data const [left, __, top] = processInput(input); // good function processInput(input) { // then a miracle occurs return { left, right, top, bottom }; } // the caller selects only the data they need const { left, right } = processInput(input);

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Strings

6.1 Use single quotes '' for strings.

// bad
const name = "Capt. Janeway"; // good const name = 'Capt. Janeway';

6.2 Strings longer than 100 characters should be written across multiple lines using string concatenation.

6.3 Note: If overused, long strings with concatenation could impact performance. jsPerf & Discussion.

// bad
const errorMessage = 'This is a super long error that was thrown because of Batman. When you stop to think about how Batman had anything to do with this, you would get nowhere fast.'; // bad const errorMessage = 'This is a super long error that was thrown because \ of Batman. When you stop to think about how Batman had anything to do \ with this, you would get nowhere \ fast.'; // good const errorMessage = 'This is a super long error that was thrown because ' + 'of Batman. When you stop to think about how Batman had anything to do ' + 'with this, you would get nowhere fast.';

6.4 When programmatically building up strings, use template strings instead of concatenation.

Why? Template strings give you a readable, concise syntax with proper newlines and string interpolation features.

  // badfunction sayHi(name) {return 'How are you, ' + name + '?'; } // bad function sayHi(name) { return ['How are you, ', name, '?'].join(); } // good function sayHi(name) { return `How are you, ${name}?`; }

6.5 Never use eval() on a string, it opens too many vulnerabilities.

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Functions

7.1 Use function declarations instead of function expressions.

Why? Function declarations are named, so they're easier to identify in call stacks. Also, the whole body of a function declaration is hoisted, whereas only the reference of a function expression is hoisted. This rule makes it possible to always use Arrow Functions in place of function expressions.
```
  // badconst foo = function () {};// good function foo() { }
```

7.2 Function expressions:

// immediately-invoked function expression (IIFE)
(() => {console.log('Welcome to the Internet. Please follow me.'); })();

7.3 Never declare a function in a non-function block (if, while, etc). Assign the function to a variable instead. Browsers will allow you to do it, but they all interpret it differently, which is bad news bears.

7.4 Note: ECMA-262 defines a block as a list of statements. A function declaration is not a statement. Read ECMA-262's note on this issue.

// bad
if (currentUser) {function test() {console.log('Nope.'); } } // good let test; if (currentUser) { test = () => { console.log('Yup.'); }; }

7.5 Never name a parameter arguments. This will take precedence over the arguments object that is given to every function scope.

// bad
function nope(name, options, arguments) { // ...stuff... } // good function yup(name, options, args) { // ...stuff... }

7.6 Never use arguments, opt to use rest syntax ... instead.

Why? ... is explicit about which arguments you want pulled. Plus rest arguments are a real Array and not Array-like like arguments.
```
  // badfunction concatenateAll() {const args = Array.prototype.slice.call(arguments); return args.join(''); } // good function concatenateAll(...args) { return args.join(''); }
```

7.7 Use default parameter syntax rather than mutating function arguments.

// really bad
function handleThings(opts) {// No! We shouldn't mutate function arguments.// Double bad: if opts is falsy it'll be set to an object which may // be what you want but it can introduce subtle bugs. opts = opts || {}; // ... } // still bad function handleThings(opts) { if (opts === void 0) { opts = {}; } // ... } // good function handleThings(opts = {}) { // ... }

7.8 Avoid side effects with default parameters.

Why? They are confusing to reason about.

var b = 1;
// bad
function count(a = b++) { console.log(a); } count(); // 1 count(); // 2 count(3); // 3 count(); // 3

7.9 Always put default parameters last.

// bad
function handleThings(opts = {}, name) { // ... } // good function handleThings(name, opts = {}) { // ... }

7.10 Never use the Function constructor to create a new function.

Why? Creating a function in this way evaluates a string similarly to eval(), which opens vulnerabilities.
```
// bad
var add = new Function('a', 'b', 'return a + b'); // still bad var subtract = Function('a', 'b', 'return a - b');
```

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Arrow Functions

8.1 When you must use function expressions (as when passing an anonymous function), use arrow function notation.

Why? It creates a version of the function that executes in the context of this, which is usually what you want, and is a more concise syntax.

Why not? If you have a fairly complicated function, you might move that logic out into its own function declaration.
```
  // bad[1, 2, 3].map(function (x) { const y = x + 1; return x * y; }); // good [1, 2, 3].map((x) => { const y = x + 1; return x * y; });
```

8.2 If the function body consists of a single expression, feel free to omit the braces and use the implicit return. Otherwise use a return statement.

Why? Syntactic sugar. It reads well when multiple functions are chained together.

Why not? If you plan on returning an object.

  // good[1, 2, 3].map(number => `A string containing the ${number}.`); // bad [1, 2, 3].map(number => { const nextNumber = number + 1; `A string containing the ${nextNumber}.`; }); // good [1, 2, 3].map(number => { const nextNumber = number + 1; return `A string containing the ${nextNumber}.`; });

8.3 In case the expression spans over multiple lines, wrap it in parentheses for better readability.

Why? It shows clearly where the function starts and ends.

  // bad[1, 2, 3].map(number => 'As time went by, the string containing the ' + `${number} became much longer. So we needed to break it over multiple ` + 'lines.' ); // good [1, 2, 3].map(number => ( `As time went by, the string containing the ${number} became much ` + 'longer. So we needed to break it over multiple lines.' ));

8.4 If your function only takes a single argument, feel free to omit the parentheses.

Why? Less visual clutter.
```
  // good[1, 2, 3].map(x => x * x); // good [1, 2, 3].reduce((y, x) => x + y);
```

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Constructors

9.1 Always use class. Avoid manipulating prototype directly.

Why? class syntax is more concise and easier to reason about.

  // badfunction Queue(contents = []) {this._queue = [...contents]; } Queue.prototype.pop = function() { const value = this._queue[0]; this._queue.splice(0, 1); return value; } // good class Queue { constructor(contents = []) { this._queue = [...contents]; } pop() { const value = this._queue[0]; this._queue.splice(0, 1); return value; } }

9.2 Use extends for inheritance.

Why? It is a built-in way to inherit prototype functionality without breaking instanceof.

  // badconst inherits = require('inherits'); function PeekableQueue(contents) { Queue.apply(this, contents); } inherits(PeekableQueue, Queue); PeekableQueue.prototype.peek = function() { return this._queue[0]; } // good class PeekableQueue extends Queue { peek() { return this._queue[0]; } }

9.3 Methods can return this to help with method chaining.

// bad
Jedi.prototype.jump = function() { this.jumping = true; return true; }; Jedi.prototype.setHeight = function(height) { this.height = height; }; const luke = new Jedi(); luke.jump(); // => true luke.setHeight(20); // => undefined // good class Jedi { jump() { this.jumping = true; return this; } setHeight(height) { this.height = height; return this; } } const luke = new Jedi(); luke.jump() .setHeight(20);

9.4 It's okay to write a custom toString() method, just make sure it works successfully and causes no side effects.

class Jedi {constructor(options = {}) {this.name = options.name || 'no name'; } getName() { return this.name; } toString() { return `Jedi - ${this.getName()}`; } }

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Modules

10.1 Always use modules (import/export) over a non-standard module system. You can always transpile to your preferred module system.

Why? Modules are the future, let's start using the future now.

  // badconst AirbnbStyleGuide = require('./AirbnbStyleGuide'); module.exports = AirbnbStyleGuide.es6; // ok import AirbnbStyleGuide from './AirbnbStyleGuide'; export default AirbnbStyleGuide.es6; // best import { es6 } from './AirbnbStyleGuide'; export default es6;

10.2 Do not use wildcard imports.

Why? This makes sure you have a single default export.

  // badimport * as AirbnbStyleGuide from './AirbnbStyleGuide'; // good import AirbnbStyleGuide from './AirbnbStyleGuide';

10.3 And do not export directly from an import.

Why? Although the one-liner is concise, having one clear way to import and one clear way to export makes things consistent.
```
  // bad// filename es6.jsexport { es6 as default } from './airbnbStyleGuide'; // good // filename es6.js import { es6 } from './AirbnbStyleGuide'; export default es6;
```

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Iterators and Generators

11.1 Don't use iterators. Prefer JavaScript's higher-order functions like map() and reduce() instead of loops like for-of.

Why? This enforces our immutable rule. Dealing with pure functions that return values is easier to reason about than side-effects.

  const numbers = [1, 2, 3, 4, 5]; // bad let sum = 0; for (let num of numbers) { sum += num; } sum === 15; // good let sum = 0; numbers.forEach((num) => sum += num); sum === 15; // best (use the functional force) const sum = numbers.reduce((total, num) => total + num, 0); sum === 15;

11.2 Don't use generators for now.

Why? They don't transpile well to ES5.

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Properties

12.1 Use dot notation when accessing properties.

const luke = {jedi: true,age: 28, }; // bad const isJedi = luke['jedi']; // good const isJedi = luke.jedi;

12.2 Use subscript notation [] when accessing properties with a variable.

const luke = {jedi: true,age: 28, }; function getProp(prop) { return luke[prop]; } const isJedi = getProp('jedi');

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Variables

13.1 Always use const to declare variables. Not doing so will result in global variables. We want to avoid polluting the global namespace. Captain Planet warned us of that.
```
// bad
superPower = new SuperPower();// good
const superPower = new SuperPower();
```

13.2 Use one const declaration per variable.

Why? It's easier to add new variable declarations this way, and you never have to worry about swapping out a ; for a , or introducing punctuation-only diffs.

// bad
const items = getItems(),goSportsTeam = true, dragonball = 'z'; // bad // (compare to above, and try to spot the mistake) const items = getItems(), goSportsTeam = true; dragonball = 'z'; // good const items = getItems(); const goSportsTeam = true; const dragonball = 'z';

13.3 Group all your consts and then group all your lets.

Why? This is helpful when later on you might need to assign a variable depending on one of the previous assigned variables.

  // badlet i, len, dragonball,items = getItems(),goSportsTeam = true;// bad let i; const items = getItems(); let dragonball; const goSportsTeam = true; let len; // good const goSportsTeam = true; const items = getItems(); let dragonball; let i; let length;

13.4 Assign variables where you need them, but place them in a reasonable place.

Why? let and const are block scoped and not function scoped.

  // goodfunction() {test();console.log('doing stuff..'); //..other stuff.. const name = getName(); if (name === 'test') { return false; } return name; } // bad - unnecessary function call function(hasName) { const name = getName(); if (!hasName) { return false; } this.setFirstName(name); return true; } // good function(hasName) { if (!hasName) { return false; } const name = getName(); this.setFirstName(name); return true; }

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Hoisting

14.1 var declarations get hoisted to the top of their scope, their assignment does not. const and let declarations are blessed with a new concept called Temporal Dead Zones (TDZ). It's important to know why typeof is no longer safe.

// we know this wouldn't work (assuming there
// is no notDefined global variable)
function example() {console.log(notDefined); // => throws a ReferenceError } // creating a variable declaration after you // reference the variable will work due to // variable hoisting. Note: the assignment // value of `true` is not hoisted. function example() { console.log(declaredButNotAssigned); // => undefined var declaredButNotAssigned = true; } // The interpreter is hoisting the variable // declaration to the top of the scope, // which means our example could be rewritten as: function example() { let declaredButNotAssigned; console.log(declaredButNotAssigned); // => undefined declaredButNotAssigned = true; } // using const and let function example() { console.log(declaredButNotAssigned); // => throws a ReferenceError console.log(typeof declaredButNotAssigned); // => throws a ReferenceError const declaredButNotAssigned = true; }

14.2 Anonymous function expressions hoist their variable name, but not the function assignment.

function example() {console.log(anonymous); // => undefinedanonymous(); // => TypeError anonymous is not a function var anonymous = function() { console.log('anonymous function expression'); }; }

14.3 Named function expressions hoist the variable name, not the function name or the function body.

function example() {console.log(named); // => undefinednamed(); // => TypeError named is not a function superPower(); // => ReferenceError superPower is not defined var named = function superPower() { console.log('Flying'); }; } // the same is true when the function name // is the same as the variable name. function example() { console.log(named); // => undefined named(); // => TypeError named is not a function var named = function named() { console.log('named'); } }

14.4 Function declarations hoist their name and the function body.

function example() {superPower(); // => Flyingfunction superPower() {console.log('Flying'); } }

For more information refer to JavaScript Scoping & Hoisting by Ben Cherry.

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Comparison Operators & Equality

15.1 Use === and !== over == and !=.
15.2 Conditional statements such as the if statement evaluate their expression using coercion with the ToBoolean abstract method and always follow these simple rules:
- Objects evaluate to true
- Undefined evaluates to false
- Null evaluates to false
- Booleans evaluate to the value of the boolean
- Numbers evaluate to false if +0, -0, or NaN, otherwise true
- Strings evaluate to false if an empty string '', otherwise true
```
if ([0]) {// true// An array is an object, objects evaluate to true
}
```

15.3 Use shortcuts.

// bad
if (name !== '') { // ...stuff... } // good if (name) { // ...stuff... } // bad if (collection.length > 0) { // ...stuff... } // good if (collection.length) { // ...stuff... }

15.4 For more information see Truth Equality and JavaScript by Angus Croll.

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Blocks

16.1 Use braces with all multi-line blocks.

// bad
if (test)return false;// good
if (test) return false; // good if (test) { return false; } // bad function() { return false; } // good function() { return false; }

16.2 If you're using multi-line blocks with if and else, put else on the same line as yourif block's closing brace.

// bad
if (test) {thing1();thing2();
}
else {thing3();
}// good
if (test) {thing1();thing2();
} else { thing3(); }

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Comments

17.1 Use /** ... */ for multi-line comments. Include a description, specify types and values for all parameters and return values.

// bad
// make() returns a new element
// based on the passed in tag name
//
// @param {String} tag
// @return {Element} element function make(tag) { // ...stuff... return element; } // good /**  * make() returns a new element  * based on the passed in tag name  *  * @param {String} tag  * @return {Element} element  */ function make(tag) { // ...stuff... return element; }

17.2 Use // for single line comments. Place single line comments on a newline above the subject of the comment. Put an empty line before the comment.

// bad
const active = true;  // is current tab // good // is current tab const active = true; // bad function getType() { console.log('fetching type...'); // set the default type to 'no type' const type = this._type || 'no type'; return type; } // good function getType() { console.log('fetching type...'); // set the default type to 'no type' const type = this._type || 'no type'; return type; }

17.3 Prefixing your comments with FIXME or TODO helps other developers quickly understand if you're pointing out a problem that needs to be revisited, or if you're suggesting a solution to the problem that needs to be implemented. These are different than regular comments because they are actionable. The actions are FIXME -- need to figure this out or TODO -- need to implement.

17.4 Use // FIXME: to annotate problems.

class Calculator extends Abacus {constructor() {super(); // FIXME: shouldn't use a global here total = 0; } }

17.5 Use // TODO: to annotate solutions to problems.

class Calculator extends Abacus {constructor() {super(); // TODO: total should be configurable by an options param this.total = 0; } }

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Whitespace

18.1 Use soft tabs set to 2 spaces.

// bad
function() {
∙∙∙∙const name;
}// bad
function() { ∙const name; } // good function() { ∙∙const name; }

18.2 Place 1 space before the leading brace.

// bad
function test(){console.log('test'); } // good function test() { console.log('test'); } // bad dog.set('attr',{ age: '1 year', breed: 'Bernese Mountain Dog', }); // good dog.set('attr', { age: '1 year', breed: 'Bernese Mountain Dog', });

18.3 Place 1 space before the opening parenthesis in control statements (if, while etc.). Place no space before the argument list in function calls and declarations.

// bad
if(isJedi) {fight ();
}// good
if (isJedi) {fight();
}// bad
function fight () { console.log ('Swooosh!'); } // good function fight() { console.log('Swooosh!'); }

18.4 Set off operators with spaces.

// bad
const x=y+5; // good const x = y + 5;

18.5 End files with a single newline character.

// bad
(function(global) {// ...stuff...
})(this);

// bad
(function(global) {// ...stuff...
})(this);↵
↵

// good
(function(global) {// ...stuff...
})(this);↵

18.6 Use indentation when making long method chains. Use a leading dot, whichemphasizes that the line is a method call, not a new statement.

// bad
$('#items').find('.selected').highlight().end().find('.open').updateCount(); // bad $('#items'). find('.selected'). highlight(). end(). find('.open'). updateCount(); // good $('#items') .find('.selected') .highlight() .end() .find('.open') .updateCount(); // bad const leds = stage.selectAll('.led').data(data).enter().append('svg:svg').class('led', true) .attr('width', (radius + margin) * 2).append('svg:g') .attr('transform', 'translate(' + (radius + margin) + ',' + (radius + margin) + ')') .call(tron.led); // good const leds = stage.selectAll('.led') .data(data) .enter().append('svg:svg') .classed('led', true) .attr('width', (radius + margin) * 2) .append('svg:g') .attr('transform', 'translate(' + (radius + margin) + ',' + (radius + margin) + ')') .call(tron.led);

18.7 Leave a blank line after blocks and before the next statement.

// bad
if (foo) {return bar;
}
return baz;// good
if (foo) { return bar; } return baz; // bad const obj = { foo() { }, bar() { }, }; return obj; // good const obj = { foo() { }, bar() { }, }; return obj; // bad const arr = [ function foo() { }, function bar() { }, ]; return arr; // good const arr = [ function foo() { }, function bar() { }, ]; return arr;

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Commas

19.1 Leading commas: Nope.

// bad
const story = [once, upon, aTime
];// good
const story = [ once, upon, aTime, ]; // bad const hero = { firstName: 'Ada' , lastName: 'Lovelace' , birthYear: 1815 , superPower: 'computers' }; // good const hero = { firstName: 'Ada', lastName: 'Lovelace', birthYear: 1815, superPower: 'computers', };

19.2 Additional trailing comma: Yup.

Why? This leads to cleaner git diffs. Also, transpilers like Babel will remove the additional trailing comma in the transpiled code which means you don't have to worry about the trailing comma problem in legacy browsers.

  // bad - git diff without trailing commaconst hero = {firstName: 'Florence', - lastName: 'Nightingale' + lastName: 'Nightingale', + inventorOf: ['coxcomb graph', 'modern nursing'] }; // good - git diff with trailing comma const hero = { firstName: 'Florence', lastName: 'Nightingale', + inventorOf: ['coxcomb chart', 'modern nursing'], }; // bad const hero = { firstName: 'Dana', lastName: 'Scully' }; const heroes = [ 'Batman', 'Superman' ]; // good const hero = { firstName: 'Dana', lastName: 'Scully', }; const heroes = [ 'Batman', 'Superman', ];

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Semicolons

20.1 Yup.

// bad
(function() {const name = 'Skywalker' return name })() // good (() => { const name = 'Skywalker'; return name; })(); // good (guards against the function becoming an argument when two files with IIFEs are concatenated) ;(() => { const name = 'Skywalker'; return name; })();

Type Casting & Coercion

21.1 Perform type coercion at the beginning of the statement.

21.2 Strings:

//  => this.reviewScore = 9;// bad
const totalScore = this.reviewScore + ''; // good const totalScore = String(this.reviewScore);

21.3 Use parseInt for Numbers and always with a radix for type casting.

const inputValue = '4'; // bad const val = new Number(inputValue); // bad const val = +inputValue; // bad const val = inputValue >> 0; // bad const val = parseInt(inputValue); // good const val = Number(inputValue); // good const val = parseInt(inputValue, 10);

21.4 If for whatever reason you are doing something wild and parseInt is your bottleneck and need to use Bitshift for performance reasons, leave a comment explaining why and what you're doing.
```
// good
/**
 * parseInt was the reason my code was slow.
 * Bitshifting the String to coerce it to a
 * Number made it a lot faster.
 */ const val = inputValue >> 0;
```
21.5 Note: Be careful when using bitshift operations. Numbers are represented as 64-bit values, but Bitshift operations always return a 32-bit integer (source). Bitshift can lead to unexpected behavior for integer values larger than 32 bits. Discussion. Largest signed 32-bit Int is 2,147,483,647:
```
2147483647 >> 0 //=> 2147483647
2147483648 >> 0 //=> -2147483648 2147483649 >> 0 //=> -2147483647
```

21.6 Booleans:

const age = 0;// bad
const hasAge = new Boolean(age); // good const hasAge = Boolean(age); // good const hasAge = !!age;

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Naming Conventions

22.1 Avoid single letter names. Be descriptive with your naming.

// bad
function q() {// ...stuff...
}// good
function query() { // ..stuff.. }

22.2 Use camelCase when naming objects, functions, and instances.

// bad
const OBJEcttsssss = {};
const this_is_my_object = {}; function c() {} // good const thisIsMyObject = {}; function thisIsMyFunction() {}

22.3 Use PascalCase when naming constructors or classes.

// bad
function user(options) {this.name = options.name; } const bad = new user({ name: 'nope', }); // good class User { constructor(options) { this.name = options.name; } } const good = new User({ name: 'yup', });

22.4 Use a leading underscore _ when naming private properties.

// bad
this.__firstName__ = 'Panda'; this.firstName_ = 'Panda'; // good this._firstName = 'Panda';

22.5 Don't save references to this. Use arrow functions or Function#bind.

// bad
function foo() {const self = this; return function() { console.log(self); }; } // bad function foo() { const that = this; return function() { console.log(that); }; } // good function foo() { return () => { console.log(this); }; }

22.6 If your file exports a single class, your filename should be exactly the name of the class.

// file contents
class CheckBox {// ...
}
export default CheckBox; // in some other file // bad import CheckBox from './checkBox'; // bad import CheckBox from './check_box'; // good import CheckBox from './CheckBox';

22.7 Use camelCase when you export-default a function. Your filename should be identical to your function's name.
```
function makeStyleGuide() {
}export default makeStyleGuide;
```
22.8 Use PascalCase when you export a singleton / function library / bare object.
```
const AirbnbStyleGuide = {es6: {}
};export default AirbnbStyleGuide;
```

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Accessors

23.1 Accessor functions for properties are not required.

23.2 If you do make accessor functions use getVal() and setVal('hello').

// bad
dragon.age();// good
dragon.getAge();// bad
dragon.age(25);// good
dragon.setAge(25);

23.3 If the property is a boolean, use isVal() or hasVal().

// bad
if (!dragon.age()) {return false;
}// good if (!dragon.hasAge()) { return false; }

23.4 It's okay to create get() and set() functions, but be consistent.

class Jedi {constructor(options = {}) {const lightsaber = options.lightsaber || 'blue'; this.set('lightsaber', lightsaber); } set(key, val) { this[key] = val; } get(key) { return this[key]; } }

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Events

24.1 When attaching data payloads to events (whether DOM events or something more proprietary like Backbone events), pass a hash instead of a raw value. This allows a subsequent contributor to add more data to the event payload without finding and updating every handler for the event. For example, instead of:
```
// bad
$(this).trigger('listingUpdated', listing.id); ... $(this).on('listingUpdated', function(e, listingId) { // do something with listingId });
```
prefer:
```
// good
$(this).trigger('listingUpdated', { listingId: listing.id }); ... $(this).on('listingUpdated', function(e, data) { // do something with data.listingId });
```
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jQuery

25.1 Prefix jQuery object variables with a $.

// bad
const sidebar = $('.sidebar'); // good const $sidebar = $('.sidebar'); // good const $sidebarBtn = $('.sidebar-btn');

25.2 Cache jQuery lookups.

// bad
function setSidebar() {$('.sidebar').hide(); // ...stuff... $('.sidebar').css({ 'background-color': 'pink' }); } // good function setSidebar() { const $sidebar = $('.sidebar'); $sidebar.hide(); // ...stuff... $sidebar.css({ 'background-color': 'pink' }); }

25.3 For DOM queries use Cascading $('.sidebar ul') or parent > child $('.sidebar > ul'). jsPerf

25.4 Use find with scoped jQuery object queries.

// bad
$('ul', '.sidebar').hide(); // bad $('.sidebar').find('ul').hide(); // good $('.sidebar ul').hide(); // good $('.sidebar > ul').hide(); // good $sidebar.find('ul').hide();

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ECMAScript 5 Compatibility

26.1 Refer to Kangax's ES5 compatibility table.

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ECMAScript 6 Styles

27.1 This is a collection of links to the various es6 features.

Arrow Functions
Classes
Object Shorthand
Object Concise
Object Computed Properties
Template Strings
Destructuring
Default Parameters
Rest
Array Spreads
Let and Const
Iterators and Generators
Modules

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Testing

28.1 Yup.
```
function() {return true;
}
```

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Performance

On Layout & Web Performance
String vs Array Concat
Try/Catch Cost In a Loop
Bang Function
jQuery Find vs Context, Selector
innerHTML vs textContent for script text
Long String Concatenation
Loading...

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Resources

Learning ES6

Draft ECMA 2015 (ES6) Spec
ExploringJS
ES6 Compatibility Table
Comprehensive Overview of ES6 Features

Read This

Standard ECMA-262

Tools

Code Style Linters
- ESlint - Airbnb Style .eslintrc
- JSHint - Airbnb Style .jshintrc
- JSCS - Airbnb Style Preset

Other Style Guides

Google JavaScript Style Guide
jQuery Core Style Guidelines
Principles of Writing Consistent, Idiomatic JavaScript

Other Styles

Naming this in nested functions - Christian Johansen
Conditional Callbacks - Ross Allen
Popular JavaScript Coding Conventions on Github - JeongHoon Byun
Multiple var statements in JavaScript, not superfluous - Ben Alman

Further Reading

Understanding JavaScript Closures - Angus Croll
Basic JavaScript for the impatient programmer - Dr. Axel Rauschmayer
You Might Not Need jQuery - Zack Bloom & Adam Schwartz
ES6 Features - Luke Hoban
Frontend Guidelines - Benjamin De Cock

Books

JavaScript: The Good Parts - Douglas Crockford
JavaScript Patterns - Stoyan Stefanov
Pro JavaScript Design Patterns - Ross Harmes and Dustin Diaz
High Performance Web Sites: Essential Knowledge for Front-End Engineers - Steve Souders
Maintainable JavaScript - Nicholas C. Zakas
JavaScript Web Applications - Alex MacCaw
Pro JavaScript Techniques - John Resig
Smashing Node.js: JavaScript Everywhere - Guillermo Rauch
Secrets of the JavaScript Ninja - John Resig and Bear Bibeault
Human JavaScript - Henrik Joreteg
Superhero.js - Kim Joar Bekkelund, Mads Mobæk, & Olav Bjorkoy
JSBooks - Julien Bouquillon
Third Party JavaScript - Ben Vinegar and Anton Kovalyov
Effective JavaScript: 68 Specific Ways to Harness the Power of JavaScript - David Herman
Eloquent JavaScript - Marijn Haverbeke
You Don't Know JS: ES6 & Beyond - Kyle Simpson

Blogs

DailyJS
JavaScript Weekly
JavaScript, JavaScript...
Bocoup Weblog
Adequately Good
NCZOnline
Perfection Kills
Ben Alman
Dmitry Baranovskiy
Dustin Diaz
nettuts

Podcasts

JavaScript Jabber

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In the Wild

This is a list of organizations that are using this style guide. Send us a pull request and we'll add you to the list.

Aan Zee: AanZee/javascript
Adult Swim: adult-swim/javascript
Airbnb: airbnb/javascript
Apartmint: apartmint/javascript
Avalara: avalara/javascript
Billabong: billabong/javascript
Blendle: blendle/javascript
ComparaOnline: comparaonline/javascript
Compass Learning: compasslearning/javascript-style-guide
DailyMotion: dailymotion/javascript
Digitpaint digitpaint/javascript
Evernote: evernote/javascript-style-guide
ExactTarget: ExactTarget/javascript
Expensify Expensify/Style-Guide
Flexberry: Flexberry/javascript-style-guide
Gawker Media: gawkermedia/javascript
General Electric: GeneralElectric/javascript
GoodData: gooddata/gdc-js-style
Grooveshark: grooveshark/javascript
How About We: howaboutwe/javascript
Huballin: huballin/javascript
Hyper: hyperoslo/javascript-playbook
InfoJobs: InfoJobs/JavaScript-Style-Guide
Intent Media: intentmedia/javascript
Jam3: Jam3/Javascript-Code-Conventions
JSSolutions: JSSolutions/javascript
Kinetica Solutions: kinetica/javascript
Mighty Spring: mightyspring/javascript
MinnPost: MinnPost/javascript
MitocGroup: MitocGroup/javascript
ModCloth: modcloth/javascript
Money Advice Service: moneyadviceservice/javascript
Muber: muber/javascript
National Geographic: natgeo/javascript
National Park Service: nationalparkservice/javascript
Nimbl3: nimbl3/javascript
Orion Health: orionhealth/javascript
Peerby: Peerby/javascript
Razorfish: razorfish/javascript-style-guide
reddit: reddit/styleguide/javascript
REI: reidev/js-style-guide
Ripple: ripple/javascript-style-guide
SeekingAlpha: seekingalpha/javascript-style-guide
Shutterfly: shutterfly/javascript
Springload: springload/javascript
StudentSphere: studentsphere/javascript
Target: target/javascript
TheLadders: TheLadders/javascript
T4R Technology: T4R-Technology/javascript
VoxFeed: VoxFeed/javascript-style-guide
Weggo: Weggo/javascript
Zillow: zillow/javascript
ZocDoc: ZocDoc/javascript

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Translation

This style guide is also available in other languages:

Brazilian Portuguese: armoucar/javascript-style-guide
Bulgarian: borislavvv/javascript
Catalan: fpmweb/javascript-style-guide
Chinese (Simplified): sivan/javascript-style-guide
Chinese (Traditional): jigsawye/javascript
French: nmussy/javascript-style-guide
German: timofurrer/javascript-style-guide
Italian: sinkswim/javascript-style-guide
Japanese: mitsuruog/javacript-style-guide
Korean: tipjs/javascript-style-guide
Polish: mjurczyk/javascript
Russian: uprock/javascript
Spanish: paolocarrasco/javascript-style-guide
Thai: lvarayut/javascript-style-guide

The JavaScript Style Guide Guide

Reference

Chat With Us About JavaScript

Find us on gitter.

Contributors

View Contributors

License

(The MIT License)

Permission is hereby granted, free of charge, to any person obtaininga copy of this software and associated documentation files (the'Software'), to deal in the Software without restriction, includingwithout limitation the rights to use, copy, modify, merge, publish,distribute, sublicense, and/or sell copies of the Software, and topermit persons to whom the Software is furnished to do so, subject tothe following conditions:

The above copyright notice and this permission notice shall beincluded in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND,EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OFMERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANYCLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THESOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

⬆ back to top

Amendments

We encourage you to fork this guide and change the rules to fit your team's style guide. Below, you may list some amendments to the style guide. This allows you to periodically update your style guide without having to deal with merge conflicts.

};

转自： https://github.com/airbnb/javascript/blob/master/README.md

Airbnb JavaScript Style Guide() {

A mostly reasonable approach to JavaScript

Other Style Guides

ES5
React
CSS & Sass
Ruby

Types
References
Objects
Arrays
Destructuring
Strings
Functions
Arrow Functions
Constructors
Modules
Iterators and Generators
Properties
Variables
Hoisting
Comparison Operators & Equality
Blocks
Comments
Whitespace
Commas
Semicolons
Type Casting & Coercion
Naming Conventions
Accessors
Events
jQuery
ECMAScript 5 Compatibility
ECMAScript 6 Styles
Testing
Performance
Resources
In the Wild
Translation
The JavaScript Style Guide Guide
Chat With Us About JavaScript
Contributors
License

Types

1.1 Primitives: When you access a primitive type you work directly on its value.
- string
- number
- boolean
- null
- undefined
```
const foo = 1;
let bar = foo; bar = 9; console.log(foo, bar); // => 1, 9
```
1.2 Complex: When you access a complex type you work on a reference to its value.
- object
- array
- function
```
const foo = [1, 2];
const bar = foo; bar[0] = 9; console.log(foo[0], bar[0]); // => 9, 9
```

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References

2.1 Use const for all of your references; avoid using var.

Why? This ensures that you can't reassign your references (mutation), which can lead to bugs and difficult to comprehend code.
```
  // badvar a = 1;var b = 2; // good const a = 1; const b = 2;
```
2.2 If you must mutate references, use let instead of var.

Why? let is block-scoped rather than function-scoped like var.
```
  // badvar count = 1;if (true) { count += 1; } // good, use the let. let count = 1; if (true) { count += 1; }
```

2.3 Note that both let and const are block-scoped.

// const and let only exist in the blocks they are defined in.
{let a = 1;const b = 1; } console.log(a); // ReferenceError console.log(b); // ReferenceError

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Objects

3.1 Use the literal syntax for object creation.

// bad
const item = new Object(); // good const item = {};

3.2 If your code will be executed in browsers in script context, don't use reserved words as keys. It won't work in IE8. More info. It’s OK to use them in ES6 modules and server-side code.
```
// bad
const superman = {default: { clark: 'kent' }, private: true, }; // good const superman = { defaults: { clark: 'kent' }, hidden: true, };
```

3.3 Use readable synonyms in place of reserved words.

// bad
const superman = {class: 'alien', }; // bad const superman = { klass: 'alien', }; // good const superman = { type: 'alien', };

3.4 Use computed property names when creating objects with dynamic property names.

Why? They allow you to define all the properties of an object in one place.

  function getKey(k) {return `a key named ${k}`; } // bad const obj = { id: 5, name: 'San Francisco', }; obj[getKey('enabled')] = true; // good const obj = { id: 5, name: 'San Francisco', [getKey('enabled')]: true, };

3.5 Use object method shorthand.

// bad
const atom = {value: 1, addValue: function (value) { return atom.value + value; }, }; // good const atom = { value: 1, addValue(value) { return atom.value + value; }, };

3.6 Use property value shorthand.

Why? It is shorter to write and descriptive.

  const lukeSkywalker = 'Luke Skywalker'; // bad const obj = { lukeSkywalker: lukeSkywalker, }; // good const obj = { lukeSkywalker, };

3.7 Group your shorthand properties at the beginning of your object declaration.

Why? It's easier to tell which properties are using the shorthand.

  const anakinSkywalker = 'Anakin Skywalker'; const lukeSkywalker = 'Luke Skywalker'; // bad const obj = { episodeOne: 1, twoJediWalkIntoACantina: 2, lukeSkywalker, episodeThree: 3, mayTheFourth: 4, anakinSkywalker, }; // good const obj = { lukeSkywalker, anakinSkywalker, episodeOne: 1, twoJediWalkIntoACantina: 2, episodeThree: 3, mayTheFourth: 4, };

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Arrays

4.1 Use the literal syntax for array creation.

// bad
const items = new Array(); // good const items = [];

4.2 Use Array#push instead of direct assignment to add items to an array.

const someStack = [];// bad
someStack[someStack.length] = 'abracadabra'; // good someStack.push('abracadabra');

4.3 Use array spreads ... to copy arrays.

// bad
const len = items.length;
const itemsCopy = []; let i; for (i = 0; i < len; i++) { itemsCopy[i] = items[i]; } // good const itemsCopy = [...items];

4.4 To convert an array-like object to an array, use Array#from.

const foo = document.querySelectorAll('.foo'); const nodes = Array.from(foo);

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Destructuring

5.1 Use object destructuring when accessing and using multiple properties of an object.

Why? Destructuring saves you from creating temporary references for those properties.

  // badfunction getFullName(user) {const firstName = user.firstName; const lastName = user.lastName; return `${firstName} ${lastName}`; } // good function getFullName(obj) { const { firstName, lastName } = obj; return `${firstName} ${lastName}`; } // best function getFullName({ firstName, lastName }) { return `${firstName} ${lastName}`; }

5.2 Use array destructuring.

const arr = [1, 2, 3, 4]; // bad const first = arr[0]; const second = arr[1]; // good const [first, second] = arr;

5.3 Use object destructuring for multiple return values, not array destructuring.

Why? You can add new properties over time or change the order of things without breaking call sites.

  // badfunction processInput(input) {// then a miracle occursreturn [left, right, top, bottom]; } // the caller needs to think about the order of return data const [left, __, top] = processInput(input); // good function processInput(input) { // then a miracle occurs return { left, right, top, bottom }; } // the caller selects only the data they need const { left, right } = processInput(input);

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Strings

6.1 Use single quotes '' for strings.

// bad
const name = "Capt. Janeway"; // good const name = 'Capt. Janeway';

6.2 Strings longer than 100 characters should be written across multiple lines using string concatenation.

6.3 Note: If overused, long strings with concatenation could impact performance. jsPerf & Discussion.

// bad
const errorMessage = 'This is a super long error that was thrown because of Batman. When you stop to think about how Batman had anything to do with this, you would get nowhere fast.'; // bad const errorMessage = 'This is a super long error that was thrown because \ of Batman. When you stop to think about how Batman had anything to do \ with this, you would get nowhere \ fast.'; // good const errorMessage = 'This is a super long error that was thrown because ' + 'of Batman. When you stop to think about how Batman had anything to do ' + 'with this, you would get nowhere fast.';

6.4 When programmatically building up strings, use template strings instead of concatenation.

Why? Template strings give you a readable, concise syntax with proper newlines and string interpolation features.

  // badfunction sayHi(name) {return 'How are you, ' + name + '?'; } // bad function sayHi(name) { return ['How are you, ', name, '?'].join(); } // good function sayHi(name) { return `How are you, ${name}?`; }

6.5 Never use eval() on a string, it opens too many vulnerabilities.

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Functions

7.1 Use function declarations instead of function expressions.

Why? Function declarations are named, so they're easier to identify in call stacks. Also, the whole body of a function declaration is hoisted, whereas only the reference of a function expression is hoisted. This rule makes it possible to always use Arrow Functions in place of function expressions.
```
  // badconst foo = function () {};// good function foo() { }
```

7.2 Function expressions:

// immediately-invoked function expression (IIFE)
(() => {console.log('Welcome to the Internet. Please follow me.'); })();

7.3 Never declare a function in a non-function block (if, while, etc). Assign the function to a variable instead. Browsers will allow you to do it, but they all interpret it differently, which is bad news bears.

7.4 Note: ECMA-262 defines a block as a list of statements. A function declaration is not a statement. Read ECMA-262's note on this issue.

// bad
if (currentUser) {function test() {console.log('Nope.'); } } // good let test; if (currentUser) { test = () => { console.log('Yup.'); }; }

7.5 Never name a parameter arguments. This will take precedence over the arguments object that is given to every function scope.

// bad
function nope(name, options, arguments) { // ...stuff... } // good function yup(name, options, args) { // ...stuff... }

7.6 Never use arguments, opt to use rest syntax ... instead.

Why? ... is explicit about which arguments you want pulled. Plus rest arguments are a real Array and not Array-like like arguments.
```
  // badfunction concatenateAll() {const args = Array.prototype.slice.call(arguments); return args.join(''); } // good function concatenateAll(...args) { return args.join(''); }
```

7.7 Use default parameter syntax rather than mutating function arguments.

// really bad
function handleThings(opts) {// No! We shouldn't mutate function arguments.// Double bad: if opts is falsy it'll be set to an object which may // be what you want but it can introduce subtle bugs. opts = opts || {}; // ... } // still bad function handleThings(opts) { if (opts === void 0) { opts = {}; } // ... } // good function handleThings(opts = {}) { // ... }

7.8 Avoid side effects with default parameters.

Why? They are confusing to reason about.

var b = 1;
// bad
function count(a = b++) { console.log(a); } count(); // 1 count(); // 2 count(3); // 3 count(); // 3

7.9 Always put default parameters last.

// bad
function handleThings(opts = {}, name) { // ... } // good function handleThings(name, opts = {}) { // ... }

7.10 Never use the Function constructor to create a new function.

Why? Creating a function in this way evaluates a string similarly to eval(), which opens vulnerabilities.
```
// bad
var add = new Function('a', 'b', 'return a + b'); // still bad var subtract = Function('a', 'b', 'return a - b');
```

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Arrow Functions

8.1 When you must use function expressions (as when passing an anonymous function), use arrow function notation.

Why? It creates a version of the function that executes in the context of this, which is usually what you want, and is a more concise syntax.

Why not? If you have a fairly complicated function, you might move that logic out into its own function declaration.
```
  // bad[1, 2, 3].map(function (x) { const y = x + 1; return x * y; }); // good [1, 2, 3].map((x) => { const y = x + 1; return x * y; });
```

8.2 If the function body consists of a single expression, feel free to omit the braces and use the implicit return. Otherwise use a return statement.

Why? Syntactic sugar. It reads well when multiple functions are chained together.

Why not? If you plan on returning an object.

  // good[1, 2, 3].map(number => `A string containing the ${number}.`); // bad [1, 2, 3].map(number => { const nextNumber = number + 1; `A string containing the ${nextNumber}.`; }); // good [1, 2, 3].map(number => { const nextNumber = number + 1; return `A string containing the ${nextNumber}.`; });

8.3 In case the expression spans over multiple lines, wrap it in parentheses for better readability.

Why? It shows clearly where the function starts and ends.

  // bad[1, 2, 3].map(number => 'As time went by, the string containing the ' + `${number} became much longer. So we needed to break it over multiple ` + 'lines.' ); // good [1, 2, 3].map(number => ( `As time went by, the string containing the ${number} became much ` + 'longer. So we needed to break it over multiple lines.' ));

8.4 If your function only takes a single argument, feel free to omit the parentheses.

Why? Less visual clutter.
```
  // good[1, 2, 3].map(x => x * x); // good [1, 2, 3].reduce((y, x) => x + y);
```

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Constructors

9.1 Always use class. Avoid manipulating prototype directly.

Why? class syntax is more concise and easier to reason about.

  // badfunction Queue(contents = []) {this._queue = [...contents]; } Queue.prototype.pop = function() { const value = this._queue[0]; this._queue.splice(0, 1); return value; } // good class Queue { constructor(contents = []) { this._queue = [...contents]; } pop() { const value = this._queue[0]; this._queue.splice(0, 1); return value; } }

9.2 Use extends for inheritance.

Why? It is a built-in way to inherit prototype functionality without breaking instanceof.

  // badconst inherits = require('inherits'); function PeekableQueue(contents) { Queue.apply(this, contents); } inherits(PeekableQueue, Queue); PeekableQueue.prototype.peek = function() { return this._queue[0]; } // good class PeekableQueue extends Queue { peek() { return this._queue[0]; } }

9.3 Methods can return this to help with method chaining.

// bad
Jedi.prototype.jump = function() { this.jumping = true; return true; }; Jedi.prototype.setHeight = function(height) { this.height = height; }; const luke = new Jedi(); luke.jump(); // => true luke.setHeight(20); // => undefined // good class Jedi { jump() { this.jumping = true; return this; } setHeight(height) { this.height = height; return this; } } const luke = new Jedi(); luke.jump() .setHeight(20);

9.4 It's okay to write a custom toString() method, just make sure it works successfully and causes no side effects.

class Jedi {constructor(options = {}) {this.name = options.name || 'no name'; } getName() { return this.name; } toString() { return `Jedi - ${this.getName()}`; } }

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Modules

10.1 Always use modules (import/export) over a non-standard module system. You can always transpile to your preferred module system.

Why? Modules are the future, let's start using the future now.

  // badconst AirbnbStyleGuide = require('./AirbnbStyleGuide'); module.exports = AirbnbStyleGuide.es6; // ok import AirbnbStyleGuide from './AirbnbStyleGuide'; export default AirbnbStyleGuide.es6; // best import { es6 } from './AirbnbStyleGuide'; export default es6;

10.2 Do not use wildcard imports.

Why? This makes sure you have a single default export.

  // badimport * as AirbnbStyleGuide from './AirbnbStyleGuide'; // good import AirbnbStyleGuide from './AirbnbStyleGuide';

10.3 And do not export directly from an import.

Why? Although the one-liner is concise, having one clear way to import and one clear way to export makes things consistent.
```
  // bad// filename es6.jsexport { es6 as default } from './airbnbStyleGuide'; // good // filename es6.js import { es6 } from './AirbnbStyleGuide'; export default es6;
```

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Iterators and Generators

11.1 Don't use iterators. Prefer JavaScript's higher-order functions like map() and reduce() instead of loops like for-of.

Why? This enforces our immutable rule. Dealing with pure functions that return values is easier to reason about than side-effects.

  const numbers = [1, 2, 3, 4, 5]; // bad let sum = 0; for (let num of numbers) { sum += num; } sum === 15; // good let sum = 0; numbers.forEach((num) => sum += num); sum === 15; // best (use the functional force) const sum = numbers.reduce((total, num) => total + num, 0); sum === 15;

11.2 Don't use generators for now.

Why? They don't transpile well to ES5.

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Properties

12.1 Use dot notation when accessing properties.

const luke = {jedi: true,age: 28, }; // bad const isJedi = luke['jedi']; // good const isJedi = luke.jedi;

12.2 Use subscript notation [] when accessing properties with a variable.

const luke = {jedi: true,age: 28, }; function getProp(prop) { return luke[prop]; } const isJedi = getProp('jedi');

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Variables

13.1 Always use const to declare variables. Not doing so will result in global variables. We want to avoid polluting the global namespace. Captain Planet warned us of that.
```
// bad
superPower = new SuperPower();// good
const superPower = new SuperPower();
```

13.2 Use one const declaration per variable.

Why? It's easier to add new variable declarations this way, and you never have to worry about swapping out a ; for a , or introducing punctuation-only diffs.

// bad
const items = getItems(),goSportsTeam = true, dragonball = 'z'; // bad // (compare to above, and try to spot the mistake) const items = getItems(), goSportsTeam = true; dragonball = 'z'; // good const items = getItems(); const goSportsTeam = true; const dragonball = 'z';

13.3 Group all your consts and then group all your lets.

Why? This is helpful when later on you might need to assign a variable depending on one of the previous assigned variables.

  // badlet i, len, dragonball,items = getItems(),goSportsTeam = true;// bad let i; const items = getItems(); let dragonball; const goSportsTeam = true; let len; // good const goSportsTeam = true; const items = getItems(); let dragonball; let i; let length;

13.4 Assign variables where you need them, but place them in a reasonable place.

Why? let and const are block scoped and not function scoped.

  // goodfunction() {test();console.log('doing stuff..'); //..other stuff.. const name = getName(); if (name === 'test') { return false; } return name; } // bad - unnecessary function call function(hasName) { const name = getName(); if (!hasName) { return false; } this.setFirstName(name); return true; } // good function(hasName) { if (!hasName) { return false; } const name = getName(); this.setFirstName(name); return true; }

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Hoisting

// we know this wouldn't work (assuming there
// is no notDefined global variable)
function example() {console.log(notDefined); // => throws a ReferenceError } // creating a variable declaration after you // reference the variable will work due to // variable hoisting. Note: the assignment // value of `true` is not hoisted. function example() { console.log(declaredButNotAssigned); // => undefined var declaredButNotAssigned = true; } // The interpreter is hoisting the variable // declaration to the top of the scope, // which means our example could be rewritten as: function example() { let declaredButNotAssigned; console.log(declaredButNotAssigned); // => undefined declaredButNotAssigned = true; } // using const and let function example() { console.log(declaredButNotAssigned); // => throws a ReferenceError console.log(typeof declaredButNotAssigned); // => throws a ReferenceError const declaredButNotAssigned = true; }

14.2 Anonymous function expressions hoist their variable name, but not the function assignment.

function example() {console.log(anonymous); // => undefinedanonymous(); // => TypeError anonymous is not a function var anonymous = function() { console.log('anonymous function expression'); }; }

14.3 Named function expressions hoist the variable name, not the function name or the function body.

function example() {console.log(named); // => undefinednamed(); // => TypeError named is not a function superPower(); // => ReferenceError superPower is not defined var named = function superPower() { console.log('Flying'); }; } // the same is true when the function name // is the same as the variable name. function example() { console.log(named); // => undefined named(); // => TypeError named is not a function var named = function named() { console.log('named'); } }

14.4 Function declarations hoist their name and the function body.

function example() {superPower(); // => Flyingfunction superPower() {console.log('Flying'); } }

For more information refer to JavaScript Scoping & Hoisting by Ben Cherry.

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Comparison Operators & Equality

15.1 Use === and !== over == and !=.
15.2 Conditional statements such as the if statement evaluate their expression using coercion with the ToBoolean abstract method and always follow these simple rules:
- Objects evaluate to true
- Undefined evaluates to false
- Null evaluates to false
- Booleans evaluate to the value of the boolean
- Numbers evaluate to false if +0, -0, or NaN, otherwise true
- Strings evaluate to false if an empty string '', otherwise true
```
if ([0]) {// true// An array is an object, objects evaluate to true
}
```

15.3 Use shortcuts.

// bad
if (name !== '') { // ...stuff... } // good if (name) { // ...stuff... } // bad if (collection.length > 0) { // ...stuff... } // good if (collection.length) { // ...stuff... }

15.4 For more information see Truth Equality and JavaScript by Angus Croll.

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Blocks

16.1 Use braces with all multi-line blocks.

// bad
if (test)return false;// good
if (test) return false; // good if (test) { return false; } // bad function() { return false; } // good function() { return false; }

16.2 If you're using multi-line blocks with if and else, put else on the same line as yourif block's closing brace.

// bad
if (test) {thing1();thing2();
}
else {thing3();
}// good
if (test) {thing1();thing2();
} else { thing3(); }

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Comments

17.1 Use /** ... */ for multi-line comments. Include a description, specify types and values for all parameters and return values.

// bad
// make() returns a new element
// based on the passed in tag name
//
// @param {String} tag
// @return {Element} element function make(tag) { // ...stuff... return element; } // good /**  * make() returns a new element  * based on the passed in tag name  *  * @param {String} tag  * @return {Element} element  */ function make(tag) { // ...stuff... return element; }

17.2 Use // for single line comments. Place single line comments on a newline above the subject of the comment. Put an empty line before the comment.

// bad
const active = true;  // is current tab // good // is current tab const active = true; // bad function getType() { console.log('fetching type...'); // set the default type to 'no type' const type = this._type || 'no type'; return type; } // good function getType() { console.log('fetching type...'); // set the default type to 'no type' const type = this._type || 'no type'; return type; }

17.3 Prefixing your comments with FIXME or TODO helps other developers quickly understand if you're pointing out a problem that needs to be revisited, or if you're suggesting a solution to the problem that needs to be implemented. These are different than regular comments because they are actionable. The actions are FIXME -- need to figure this out or TODO -- need to implement.

17.4 Use // FIXME: to annotate problems.

class Calculator extends Abacus {constructor() {super(); // FIXME: shouldn't use a global here total = 0; } }

17.5 Use // TODO: to annotate solutions to problems.

class Calculator extends Abacus {constructor() {super(); // TODO: total should be configurable by an options param this.total = 0; } }

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Whitespace

18.1 Use soft tabs set to 2 spaces.

// bad
function() {
∙∙∙∙const name;
}// bad
function() { ∙const name; } // good function() { ∙∙const name; }

18.2 Place 1 space before the leading brace.

// bad
function test(){console.log('test'); } // good function test() { console.log('test'); } // bad dog.set('attr',{ age: '1 year', breed: 'Bernese Mountain Dog', }); // good dog.set('attr', { age: '1 year', breed: 'Bernese Mountain Dog', });

18.3 Place 1 space before the opening parenthesis in control statements (if, while etc.). Place no space before the argument list in function calls and declarations.

// bad
if(isJedi) {fight ();
}// good
if (isJedi) {fight();
}// bad
function fight () { console.log ('Swooosh!'); } // good function fight() { console.log('Swooosh!'); }

18.4 Set off operators with spaces.

// bad
const x=y+5; // good const x = y + 5;

18.5 End files with a single newline character.

// bad
(function(global) {// ...stuff...
})(this);

// bad
(function(global) {// ...stuff...
})(this);↵
↵

// good
(function(global) {// ...stuff...
})(this);↵

18.6 Use indentation when making long method chains. Use a leading dot, whichemphasizes that the line is a method call, not a new statement.

// bad
$('#items').find('.selected').highlight().end().find('.open').updateCount(); // bad $('#items'). find('.selected'). highlight(). end(). find('.open'). updateCount(); // good $('#items') .find('.selected') .highlight() .end() .find('.open') .updateCount(); // bad const leds = stage.selectAll('.led').data(data).enter().append('svg:svg').class('led', true) .attr('width', (radius + margin) * 2).append('svg:g') .attr('transform', 'translate(' + (radius + margin) + ',' + (radius + margin) + ')') .call(tron.led); // good const leds = stage.selectAll('.led') .data(data) .enter().append('svg:svg') .classed('led', true) .attr('width', (radius + margin) * 2) .append('svg:g') .attr('transform', 'translate(' + (radius + margin) + ',' + (radius + margin) + ')') .call(tron.led);

18.7 Leave a blank line after blocks and before the next statement.

// bad
if (foo) {return bar;
}
return baz;// good
if (foo) { return bar; } return baz; // bad const obj = { foo() { }, bar() { }, }; return obj; // good const obj = { foo() { }, bar() { }, }; return obj; // bad const arr = [ function foo() { }, function bar() { }, ]; return arr; // good const arr = [ function foo() { }, function bar() { }, ]; return arr;

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Commas

19.1 Leading commas: Nope.

// bad
const story = [once, upon, aTime
];// good
const story = [ once, upon, aTime, ]; // bad const hero = { firstName: 'Ada' , lastName: 'Lovelace' , birthYear: 1815 , superPower: 'computers' }; // good const hero = { firstName: 'Ada', lastName: 'Lovelace', birthYear: 1815, superPower: 'computers', };

19.2 Additional trailing comma: Yup.

Why? This leads to cleaner git diffs. Also, transpilers like Babel will remove the additional trailing comma in the transpiled code which means you don't have to worry about the trailing comma problem in legacy browsers.

  // bad - git diff without trailing commaconst hero = {firstName: 'Florence', - lastName: 'Nightingale' + lastName: 'Nightingale', + inventorOf: ['coxcomb graph', 'modern nursing'] }; // good - git diff with trailing comma const hero = { firstName: 'Florence', lastName: 'Nightingale', + inventorOf: ['coxcomb chart', 'modern nursing'], }; // bad const hero = { firstName: 'Dana', lastName: 'Scully' }; const heroes = [ 'Batman', 'Superman' ]; // good const hero = { firstName: 'Dana', lastName: 'Scully', }; const heroes = [ 'Batman', 'Superman', ];

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Semicolons

20.1 Yup.

// bad
(function() {const name = 'Skywalker' return name })() // good (() => { const name = 'Skywalker'; return name; })(); // good (guards against the function becoming an argument when two files with IIFEs are concatenated) ;(() => { const name = 'Skywalker'; return name; })();

Type Casting & Coercion

21.1 Perform type coercion at the beginning of the statement.

21.2 Strings:

//  => this.reviewScore = 9;// bad
const totalScore = this.reviewScore + ''; // good const totalScore = String(this.reviewScore);

21.3 Use parseInt for Numbers and always with a radix for type casting.

const inputValue = '4'; // bad const val = new Number(inputValue); // bad const val = +inputValue; // bad const val = inputValue >> 0; // bad const val = parseInt(inputValue); // good const val = Number(inputValue); // good const val = parseInt(inputValue, 10);

21.4 If for whatever reason you are doing something wild and parseInt is your bottleneck and need to use Bitshift for performance reasons, leave a comment explaining why and what you're doing.
```
// good
/**
 * parseInt was the reason my code was slow.
 * Bitshifting the String to coerce it to a
 * Number made it a lot faster.
 */ const val = inputValue >> 0;
```
21.5 Note: Be careful when using bitshift operations. Numbers are represented as 64-bit values, but Bitshift operations always return a 32-bit integer (source). Bitshift can lead to unexpected behavior for integer values larger than 32 bits. Discussion. Largest signed 32-bit Int is 2,147,483,647:
```
2147483647 >> 0 //=> 2147483647
2147483648 >> 0 //=> -2147483648 2147483649 >> 0 //=> -2147483647
```

21.6 Booleans:

const age = 0;// bad
const hasAge = new Boolean(age); // good const hasAge = Boolean(age); // good const hasAge = !!age;

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Naming Conventions

22.1 Avoid single letter names. Be descriptive with your naming.

// bad
function q() {// ...stuff...
}// good
function query() { // ..stuff.. }

22.2 Use camelCase when naming objects, functions, and instances.

// bad
const OBJEcttsssss = {};
const this_is_my_object = {}; function c() {} // good const thisIsMyObject = {}; function thisIsMyFunction() {}

22.3 Use PascalCase when naming constructors or classes.

// bad
function user(options) {this.name = options.name; } const bad = new user({ name: 'nope', }); // good class User { constructor(options) { this.name = options.name; } } const good = new User({ name: 'yup', });

22.4 Use a leading underscore _ when naming private properties.

// bad
this.__firstName__ = 'Panda'; this.firstName_ = 'Panda'; // good this._firstName = 'Panda';

22.5 Don't save references to this. Use arrow functions or Function#bind.

// bad
function foo() {const self = this; return function() { console.log(self); }; } // bad function foo() { const that = this; return function() { console.log(that); }; } // good function foo() { return () => { console.log(this); }; }

22.6 If your file exports a single class, your filename should be exactly the name of the class.

// file contents
class CheckBox {// ...
}
export default CheckBox; // in some other file // bad import CheckBox from './checkBox'; // bad import CheckBox from './check_box'; // good import CheckBox from './CheckBox';

22.7 Use camelCase when you export-default a function. Your filename should be identical to your function's name.
```
function makeStyleGuide() {
}export default makeStyleGuide;
```
22.8 Use PascalCase when you export a singleton / function library / bare object.
```
const AirbnbStyleGuide = {es6: {}
};export default AirbnbStyleGuide;
```

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Accessors

23.1 Accessor functions for properties are not required.

23.2 If you do make accessor functions use getVal() and setVal('hello').

// bad
dragon.age();// good
dragon.getAge();// bad
dragon.age(25);// good
dragon.setAge(25);

23.3 If the property is a boolean, use isVal() or hasVal().

// bad
if (!dragon.age()) {return false;
}// good if (!dragon.hasAge()) { return false; }

23.4 It's okay to create get() and set() functions, but be consistent.

class Jedi {constructor(options = {}) {const lightsaber = options.lightsaber || 'blue'; this.set('lightsaber', lightsaber); } set(key, val) { this[key] = val; } get(key) { return this[key]; } }

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Events

24.1 When attaching data payloads to events (whether DOM events or something more proprietary like Backbone events), pass a hash instead of a raw value. This allows a subsequent contributor to add more data to the event payload without finding and updating every handler for the event. For example, instead of:
```
// bad
$(this).trigger('listingUpdated', listing.id); ... $(this).on('listingUpdated', function(e, listingId) { // do something with listingId });
```
prefer:
```
// good
$(this).trigger('listingUpdated', { listingId: listing.id }); ... $(this).on('listingUpdated', function(e, data) { // do something with data.listingId });
```
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jQuery

25.1 Prefix jQuery object variables with a $.

// bad
const sidebar = $('.sidebar'); // good const $sidebar = $('.sidebar'); // good const $sidebarBtn = $('.sidebar-btn');

25.2 Cache jQuery lookups.

// bad
function setSidebar() {$('.sidebar').hide(); // ...stuff... $('.sidebar').css({ 'background-color': 'pink' }); } // good function setSidebar() { const $sidebar = $('.sidebar'); $sidebar.hide(); // ...stuff... $sidebar.css({ 'background-color': 'pink' }); }

25.3 For DOM queries use Cascading $('.sidebar ul') or parent > child $('.sidebar > ul'). jsPerf

25.4 Use find with scoped jQuery object queries.

// bad
$('ul', '.sidebar').hide(); // bad $('.sidebar').find('ul').hide(); // good $('.sidebar ul').hide(); // good $('.sidebar > ul').hide(); // good $sidebar.find('ul').hide();

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ECMAScript 5 Compatibility

26.1 Refer to Kangax's ES5 compatibility table.

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ECMAScript 6 Styles

27.1 This is a collection of links to the various es6 features.

Arrow Functions
Classes
Object Shorthand
Object Concise
Object Computed Properties
Template Strings
Destructuring
Default Parameters
Rest
Array Spreads
Let and Const
Iterators and Generators
Modules

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Testing

28.1 Yup.
```
function() {return true;
}
```

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Performance

On Layout & Web Performance
String vs Array Concat
Try/Catch Cost In a Loop
Bang Function
jQuery Find vs Context, Selector
innerHTML vs textContent for script text
Long String Concatenation
Loading...

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Resources

Learning ES6

Draft ECMA 2015 (ES6) Spec
ExploringJS
ES6 Compatibility Table
Comprehensive Overview of ES6 Features

Read This

Standard ECMA-262

Tools

Code Style Linters
- ESlint - Airbnb Style .eslintrc
- JSHint - Airbnb Style .jshintrc
- JSCS - Airbnb Style Preset

Other Style Guides

Google JavaScript Style Guide
jQuery Core Style Guidelines
Principles of Writing Consistent, Idiomatic JavaScript

Other Styles

Naming this in nested functions - Christian Johansen
Conditional Callbacks - Ross Allen
Popular JavaScript Coding Conventions on Github - JeongHoon Byun
Multiple var statements in JavaScript, not superfluous - Ben Alman

Further Reading

Understanding JavaScript Closures - Angus Croll
Basic JavaScript for the impatient programmer - Dr. Axel Rauschmayer
You Might Not Need jQuery - Zack Bloom & Adam Schwartz
ES6 Features - Luke Hoban
Frontend Guidelines - Benjamin De Cock

Books

JavaScript: The Good Parts - Douglas Crockford
JavaScript Patterns - Stoyan Stefanov
Pro JavaScript Design Patterns - Ross Harmes and Dustin Diaz
High Performance Web Sites: Essential Knowledge for Front-End Engineers - Steve Souders
Maintainable JavaScript - Nicholas C. Zakas
JavaScript Web Applications - Alex MacCaw
Pro JavaScript Techniques - John Resig
Smashing Node.js: JavaScript Everywhere - Guillermo Rauch
Secrets of the JavaScript Ninja - John Resig and Bear Bibeault
Human JavaScript - Henrik Joreteg
Superhero.js - Kim Joar Bekkelund, Mads Mobæk, & Olav Bjorkoy
JSBooks - Julien Bouquillon
Third Party JavaScript - Ben Vinegar and Anton Kovalyov
Effective JavaScript: 68 Specific Ways to Harness the Power of JavaScript - David Herman
Eloquent JavaScript - Marijn Haverbeke
You Don't Know JS: ES6 & Beyond - Kyle Simpson

Blogs

DailyJS
JavaScript Weekly
JavaScript, JavaScript...
Bocoup Weblog
Adequately Good
NCZOnline
Perfection Kills
Ben Alman
Dmitry Baranovskiy
Dustin Diaz
nettuts

Podcasts

JavaScript Jabber

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In the Wild

This is a list of organizations that are using this style guide. Send us a pull request and we'll add you to the list.

Aan Zee: AanZee/javascript
Adult Swim: adult-swim/javascript
Airbnb: airbnb/javascript
Apartmint: apartmint/javascript
Avalara: avalara/javascript
Billabong: billabong/javascript
Blendle: blendle/javascript
ComparaOnline: comparaonline/javascript
Compass Learning: compasslearning/javascript-style-guide
DailyMotion: dailymotion/javascript
Digitpaint digitpaint/javascript
Evernote: evernote/javascript-style-guide
ExactTarget: ExactTarget/javascript
Expensify Expensify/Style-Guide
Flexberry: Flexberry/javascript-style-guide
Gawker Media: gawkermedia/javascript
General Electric: GeneralElectric/javascript
GoodData: gooddata/gdc-js-style
Grooveshark: grooveshark/javascript
How About We: howaboutwe/javascript
Huballin: huballin/javascript
Hyper: hyperoslo/javascript-playbook
InfoJobs: InfoJobs/JavaScript-Style-Guide
Intent Media: intentmedia/javascript
Jam3: Jam3/Javascript-Code-Conventions
JSSolutions: JSSolutions/javascript
Kinetica Solutions: kinetica/javascript
Mighty Spring: mightyspring/javascript
MinnPost: MinnPost/javascript
MitocGroup: MitocGroup/javascript
ModCloth: modcloth/javascript
Money Advice Service: moneyadviceservice/javascript
Muber: muber/javascript
National Geographic: natgeo/javascript
National Park Service: nationalparkservice/javascript
Nimbl3: nimbl3/javascript
Orion Health: orionhealth/javascript
Peerby: Peerby/javascript
Razorfish: razorfish/javascript-style-guide
reddit: reddit/styleguide/javascript
REI: reidev/js-style-guide
Ripple: ripple/javascript-style-guide
SeekingAlpha: seekingalpha/javascript-style-guide
Shutterfly: shutterfly/javascript
Springload: springload/javascript
StudentSphere: studentsphere/javascript
Target: target/javascript
TheLadders: TheLadders/javascript
T4R Technology: T4R-Technology/javascript
VoxFeed: VoxFeed/javascript-style-guide
Weggo: Weggo/javascript
Zillow: zillow/javascript
ZocDoc: ZocDoc/javascript

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Translation

This style guide is also available in other languages:

Brazilian Portuguese: armoucar/javascript-style-guide
Bulgarian: borislavvv/javascript
Catalan: fpmweb/javascript-style-guide
Chinese (Simplified): sivan/javascript-style-guide
Chinese (Traditional): jigsawye/javascript
French: nmussy/javascript-style-guide
German: timofurrer/javascript-style-guide
Italian: sinkswim/javascript-style-guide
Japanese: mitsuruog/javacript-style-guide
Korean: tipjs/javascript-style-guide
Polish: mjurczyk/javascript
Russian: uprock/javascript
Spanish: paolocarrasco/javascript-style-guide
Thai: lvarayut/javascript-style-guide

The JavaScript Style Guide Guide

Reference

Chat With Us About JavaScript

Find us on gitter.

Contributors

View Contributors

License

(The MIT License)

The above copyright notice and this permission notice shall beincluded in all copies or substantial portions of the Software.

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Amendments

};

转载于:https://www.cnblogs.com/leoncfor/p/4837669.html