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原文: https://github.com/airbnb/javascript

注:本人根据自己的开发习惯删除和修改了部分规范

JavaScript规范

<a name='TOC'>内容列表</a>

  1. 类型
  2. 对象
  3. 数组
  4. 字符串
  5. 函数
  6. 属性
  7. 变量
  8. 条件表达式和等号
  9. 注释
  10. 空白
  11. 逗号
  12. 分号
  13. 类型转换
  14. 命名约定
  15. 存取器
  16. 构造器
  17. 事件
  18. 模块
  19. jQuery
  20. ES5 兼容性
  21. 性能
  22. 资源
  23. 哪些人在使用
  24. 翻译
  25. JavaScript风格指南
  26. 贡献者
  27. 许可

<a name='types'>类型</a>

<a name='objects'>对象</a>

<a name='arrays'>数组</a>

<a name='strings'>字符串</a>

<a name='functions'>函数</a>

<a name='properties'>属性</a>

<a name='variables'>变量</a>

<a name='conditionals'>条件表达式和等号</a>

<a name='blocks'></a>

<a name='comments'>注释</a>


  **[[⬆]](#TOC)**


## <a name='whitespace'>空白</a>

- 将tab设为4个空格

  ```javascript
  // bad
  function() {
  ∙∙var name;
  }

  // bad
  function() {
  ∙var name;
  }

  // good
  function() {
  ∙∙∙∙var name;
  }
  ```
- 大括号前放一个空格

  ```javascript
  // 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'
  });
  ```

- 在做长方法链时使用缩进.

  ```javascript
  // bad
  $('#items').find('.selected').highlight().end().find('.open').updateCount();

  // good
  $('#items')
    .find('.selected')
      .highlight()
      .end()
    .find('.open')
      .updateCount();

  // bad
  var 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
  var 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);
  ```

  **[[⬆]](#TOC)**

## <a name='commas'>逗号</a>

- 不要将逗号放前面

  ```javascript
  // bad
  var once
    , upon
    , aTime;

  // good
  var once,
      upon,
      aTime;

  // bad
  var hero = {
      firstName: 'Bob'
    , lastName: 'Parr'
    , heroName: 'Mr. Incredible'
    , superPower: 'strength'
  };

  // good
  var hero = {
    firstName: 'Bob',
    lastName: 'Parr',
    heroName: 'Mr. Incredible',
    superPower: 'strength'
  };
  ```

- 不要加多余的逗号,这可能会在IE下引起错误,同时如果多一个逗号某些ES3的实现会计算多数组的长度。

  ```javascript
  // bad
  var hero = {
    firstName: 'Kevin',
    lastName: 'Flynn',
  };

  var heroes = [
    'Batman',
    'Superman',
  ];

  // good
  var hero = {
    firstName: 'Kevin',
    lastName: 'Flynn'
  };

  var heroes = [
    'Batman',
    'Superman'
  ];
  ```

  **[[⬆]](#TOC)**


## <a name='semicolons'>分号</a>

- 语句结束一定要加分号

  ```javascript
  // bad
  (function() {
    var name = 'Skywalker'
    return name
  })()

  // good
  (function() {
    var name = 'Skywalker';
    return name;
  })();

  // good
  ;(function() {
    var name = 'Skywalker';
    return name;
  })();
  ```

  **[[⬆]](#TOC)**


## <a name='type-coercion'>类型转换</a>

- 在语句的开始执行类型转换.
- 字符串:

  ```javascript
  //  => this.reviewScore = 9;

  // bad
  var totalScore = this.reviewScore + '';

  // good
  var totalScore = '' + this.reviewScore;

  // bad
  var totalScore = '' + this.reviewScore + ' total score';

  // good
  var totalScore = this.reviewScore + ' total score';
  ```

- 对数字使用 `parseInt` 并且总是带上类型转换的基数.

  ```javascript
  var inputValue = '4';

  // bad
  var val = new Number(inputValue);

  // bad
  var val = +inputValue;

  // bad
  var val = inputValue >> 0;

  // bad
  var val = parseInt(inputValue);

  // good
  var val = Number(inputValue);

  // good
  var val = parseInt(inputValue, 10);

  // good
  /**
   * parseInt was the reason my code was slow.
   * Bitshifting the String to coerce it to a
   * Number made it a lot faster.
   */
  var val = inputValue >> 0;
  ```

- 布尔值:

  ```javascript
  var age = 0;

  // bad
  var hasAge = new Boolean(age);

  // good
  var hasAge = Boolean(age);

  // good
  var hasAge = !!age;
  ```

  **[[⬆]](#TOC)**


## <a name='naming-conventions'>命名约定</a>

- 避免单个字符名,让你的变量名有描述意义。

  ```javascript
  // bad
  function q() {
    // ...stuff...
  }

  // good
  function query() {
    // ..stuff..
  }
  ```

- 当命名对象、函数和实例时使用驼峰命名规则

  ```javascript
  // bad
  var OBJEcttsssss = {};
  var this_is_my_object = {};
  var this-is-my-object = {};
  function c() {};
  var u = new user({
    name: 'Bob Parr'
  });

  // good
  var thisIsMyObject = {};
  function thisIsMyFunction() {};
  var user = new User({
    name: 'Bob Parr'
  });
  ```

- 当命名构造函数或类时使用驼峰式大写

  ```javascript
  // bad
  function user(options) {
    this.name = options.name;
  }

  var bad = new user({
    name: 'nope'
  });

  // good
  function User(options) {
    this.name = options.name;
  }

  var good = new User({
    name: 'yup'
  });
  ```

- 命名私有属性时前面加个下划线 `_`

  ```javascript
  // bad
  this.__firstName__ = 'Panda';
  this.firstName_ = 'Panda';

  // good
  this._firstName = 'Panda';
  ```

- 当保存对 `this` 的引用时使用 `_this`.

  ```javascript
  // bad
  function() {
    var self = this;
    return function() {
      console.log(self);
    };
  }

  // bad
  function() {
    var that = this;
    return function() {
      console.log(that);
    };
  }

  // good
  function() {
    var _this = this;
    return function() {
      console.log(_this);
    };
  }
  ```

  **[[⬆]](#TOC)**


## <a name='accessors'>存取器</a>

- 属性的存取器函数不是必需的
- 如果你确实有存取器函数的话使用getVal() 和 setVal('hello')

  ```javascript
  // bad
  dragon.age();

  // good
  dragon.getAge();

  // bad
  dragon.age(25);

  // good
  dragon.setAge(25);
  ```

- 如果属性是布尔值,使用isVal() 或 hasVal()

  ```javascript
  // bad
  if (!dragon.age()) {
    return false;
  }

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

- 可以创建get()和set()函数,但是要保持一致

  ```javascript
  function Jedi(options) {
    options || (options = {});
    var lightsaber = options.lightsaber || 'blue';
    this.set('lightsaber', lightsaber);
  }

  Jedi.prototype.set = function(key, val) {
    this[key] = val;
  };

  Jedi.prototype.get = function(key) {
    return this[key];
  };
  ```

  **[[⬆]](#TOC)**


## <a name='constructors'>构造器</a>

- 给对象原型分配方法,而不是用一个新的对象覆盖原型,覆盖原型会使继承出现问题。

  ```javascript
  function Jedi() {
    console.log('new jedi');
  }

  // bad
  Jedi.prototype = {
    fight: function fight() {
      console.log('fighting');
    },

    block: function block() {
      console.log('blocking');
    }
  };

  // good
  Jedi.prototype.fight = function fight() {
    console.log('fighting');
  };

  Jedi.prototype.block = function block() {
    console.log('blocking');
  };
  ```

- 方法可以返回 `this` 帮助方法可链。

  ```javascript
  // bad
  Jedi.prototype.jump = function() {
    this.jumping = true;
    return true;
  };

  Jedi.prototype.setHeight = function(height) {
    this.height = height;
  };

  var luke = new Jedi();
  luke.jump(); // => true
  luke.setHeight(20) // => undefined

  // good
  Jedi.prototype.jump = function() {
    this.jumping = true;
    return this;
  };

  Jedi.prototype.setHeight = function(height) {
    this.height = height;
    return this;
  };

  var luke = new Jedi();

  luke.jump()
    .setHeight(20);
  ```


- 可以写一个自定义的toString()方法,但是确保它工作正常并且不会有副作用。

  ```javascript
  function Jedi(options) {
    options || (options = {});
    this.name = options.name || 'no name';
  }

  Jedi.prototype.getName = function getName() {
    return this.name;
  };

  Jedi.prototype.toString = function toString() {
    return 'Jedi - ' + this.getName();
  };
  ```

  **[[⬆]](#TOC)**


## <a name='events'>事件</a>

- 当给事件附加数据时,传入一个哈希而不是原始值,这可以让后面的贡献者加入更多数据到事件数据里而不用找出并更新那个事件的事件处理器

  ```js
  // bad
  $(this).trigger('listingUpdated', listing.id);

  ...

  $(this).on('listingUpdated', function(e, listingId) {
    // do something with listingId
  });
  ```

  更好:

  ```js
  // good
  $(this).trigger('listingUpdated', { listingId : listing.id });

  ...

  $(this).on('listingUpdated', function(e, data) {
    // do something with data.listingId
  });
  ```

**[[⬆]](#TOC)**


## <a name='modules'>模块</a>

- 模块应该以 `!` 开始,这保证了如果一个有问题的模块忘记包含最后的分号在合并后不会出现错误
- 这个文件应该以驼峰命名,并在同名文件夹下,同时导出的时候名字一致
- 加入一个名为noConflict()的方法来设置导出的模块为之前的版本并返回它
- 总是在模块顶部声明 `'use strict';`

  ```javascript
  // fancyInput/fancyInput.js

  !function(global) {
    'use strict';

    var previousFancyInput = global.FancyInput;

    function FancyInput(options) {
      this.options = options || {};
    }

    FancyInput.noConflict = function noConflict() {
      global.FancyInput = previousFancyInput;
      return FancyInput;
    };

    global.FancyInput = FancyInput;
  }(this);
  ```

  **[[⬆]](#TOC)**


## <a name='jquery'>jQuery</a>

- 缓存jQuery查询

  ```javascript
  // bad
  function setSidebar() {
    $('.sidebar').hide();

    // ...stuff...

    $('.sidebar').css({
      'background-color': 'pink'
    });
  }

  // good
  function setSidebar() {
    var $sidebar = $('.sidebar');
    $sidebar.hide();

    // ...stuff...

    $sidebar.css({
      'background-color': 'pink'
    });
  }
  ```

- 对DOM查询使用级联的 `$('.sidebar ul')` 或 `$('.sidebar ul')`,[jsPerf](http://jsperf.com/jquery-find-vs-context-sel/16)
- 对有作用域的jQuery对象查询使用 `find`

  ```javascript
  // bad
  $('.sidebar', 'ul').hide();

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

  // good
  $('.sidebar ul').hide();

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

  // good (slower)
  $sidebar.find('ul');

  // good (faster)
  $($sidebar[0]).find('ul');
  ```

  **[[⬆]](#TOC)**


## <a name='es5'>ECMAScript 5兼容性</a>

- 参考[Kangax](https://twitter.com/kangax/)的 ES5 [compatibility table](http://kangax.github.com/es5-compat-table/)

**[[⬆]](#TOC)**



## <a name='performance'>性能</a>

- [On Layout & Web Performance](http://kellegous.com/j/2013/01/26/layout-performance/)
- [String vs Array Concat](http://jsperf.com/string-vs-array-concat/2)
- [Try/Catch Cost In a Loop](http://jsperf.com/try-catch-in-loop-cost)
- [Bang Function](http://jsperf.com/bang-function)
- [jQuery Find vs Context, Selector](http://jsperf.com/jquery-find-vs-context-sel/13)
- [innerHTML vs textContent for script text](http://jsperf.com/innerhtml-vs-textcontent-for-script-text)
- [Long String Concatenation](http://jsperf.com/ya-string-concat)
- Loading...

**[[⬆]](#TOC)**


## <a name='resources'>资源</a>

**Read This**

- [Annotated ECMAScript 5.1](http://es5.github.com/)

**其它规范**

- [Google JavaScript Style Guide](http://google-styleguide.googlecode.com/svn/trunk/javascriptguide.xml)
- [jQuery Core Style Guidelines](http://docs.jquery.com/JQuery_Core_Style_Guidelines)
- [Principles of Writing Consistent, Idiomatic JavaScript](https://github.com/rwldrn/idiomatic.js/)

**其它风格**

- [Naming this in nested functions](https://gist.github.com/4135065) - Christian Johansen
- [Conditional Callbacks](https://github.com/airbnb/javascript/issues/52)

**阅读更多**

- [Understanding JavaScript Closures](http://javascriptweblog.wordpress.com/2010/10/25/understanding-javascript-closures/) - Angus Croll

**书籍**

- [JavaScript: The Good Parts](http://www.amazon.com/JavaScript-Good-Parts-Douglas-Crockford/dp/0596517742) - Douglas Crockford
- [JavaScript Patterns](http://www.amazon.com/JavaScript-Patterns-Stoyan-Stefanov/dp/0596806752) - Stoyan Stefanov
- [Pro JavaScript Design Patterns](http://www.amazon.com/JavaScript-Design-Patterns-Recipes-Problem-Solution/dp/159059908X)  - Ross Harmes and Dustin Diaz
- [High Performance Web Sites: Essential Knowledge for Front-End Engineers](http://www.amazon.com/High-Performance-Web-Sites-Essential/dp/0596529309) - Steve Souders
- [Maintainable JavaScript](http://www.amazon.com/Maintainable-JavaScript-Nicholas-C-Zakas/dp/1449327680) - Nicholas C. Zakas
- [JavaScript Web Applications](http://www.amazon.com/JavaScript-Web-Applications-Alex-MacCaw/dp/144930351X) - Alex MacCaw
- [Pro JavaScript Techniques](http://www.amazon.com/Pro-JavaScript-Techniques-John-Resig/dp/1590597273) - John Resig
- [Smashing Node.js: JavaScript Everywhere](http://www.amazon.com/Smashing-Node-js-JavaScript-Everywhere-Magazine/dp/1119962595) - Guillermo Rauch

**博客**

- [Adam Lu](http://adamlu.com/)
- [DailyJS](http://dailyjs.com/)
- [JavaScript Weekly](http://javascriptweekly.com/)
- [JavaScript, JavaScript...](http://javascriptweblog.wordpress.com/)
- [Bocoup Weblog](http://weblog.bocoup.com/)
- [Adequately Good](http://www.adequatelygood.com/)
- [NCZOnline](http://www.nczonline.net/)
- [Perfection Kills](http://perfectionkills.com/)
- [Ben Alman](http://benalman.com/)
- [Dmitry Baranovskiy](http://dmitry.baranovskiy.com/)
- [Dustin Diaz](http://dustindiaz.com/)
- [nettuts](http://net.tutsplus.com/?s=javascript)

**[[⬆]](#TOC)**

## <a name='in-the-wild'>哪些人在使用</a>

这是一些使用这个风格规范的组织,给我们发pull request或打开一个问题,我们会把你加到列表中。

- **Airbnb**: [airbnb/javascript](https://github.com/airbnb/javascript)
- **American Insitutes for Research**: [AIRAST/javascript](https://github.com/AIRAST/javascript)
- **ExactTarget**: [ExactTarget/javascript](https://github.com/ExactTarget/javascript)
- **GeneralElectric**: [GeneralElectric/javascript](https://github.com/GeneralElectric/javascript)
- **GoodData**: [gooddata/gdc-js-style](https://github.com/gooddata/gdc-js-style)
- **How About We**: [howaboutwe/javascript](https://github.com/howaboutwe/javascript)
- **MinnPost**: [MinnPost/javascript](https://github.com/MinnPost/javascript)
- **ModCloth**: [modcloth/javascript](https://github.com/modcloth/javascript)
- **National Geographic**: [natgeo/javascript](https://github.com/natgeo/javascript)
- **National Park Service**: [nationalparkservice/javascript](https://github.com/nationalparkservice/javascript)
- **Razorfish**: [razorfish/javascript-style-guide](https://github.com/razorfish/javascript-style-guide)
- **Shutterfly**: [shutterfly/javascript](https://github.com/shutterfly/javascript)
- **Userify**: [userify/javascript](https://github.com/userify/javascript)
- **Zillow**: [zillow/javascript](https://github.com/zillow/javascript)
- **ZocDoc**: [ZocDoc/javascript](https://github.com/ZocDoc/javascript)

## <a name='translation'>翻译</a>

这个风格规范也有其它语言版本:

- :de: **German**: [timofurrer/javascript-style-guide](https://github.com/timofurrer/javascript-style-guide)
- :jp: **Japanese**: [mitsuruog/javacript-style-guide](https://github.com/mitsuruog/javacript-style-guide)
- :br: **Portuguese**: [armoucar/javascript-style-guide](https://github.com/armoucar/javascript-style-guide)
- :cn: **Chinese**: [adamlu/javascript-style-guide](https://github.com/adamlu/javascript-style-guide)

## <a name='guide-guide'>JavaScript风格指南</a>

- [Reference](https://github.com/airbnb/javascript/wiki/The-JavaScript-Style-Guide-Guide)

## <a name='authors'>贡献者</a>

- [View Contributors](https://github.com/airbnb/javascript/graphs/contributors)


## <a name='license'>许可</a>

(The MIT License)

Copyright (c) 2012 Airbnb

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

The above copyright notice and this permission notice shall be
included 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 OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

**[[⬆]](#TOC)**

# };