javascript code style

javascript代碼風格

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

Objects 對象

javascript// bad
var item = new Object();

// good
var item = {};

//不要使用保留字做爲對象屬性，IE8不支持。
// bad
var superman = {
  default: { clark: 'kent' },
  private: true
};

// good
var superman = {
  defaults: { clark: 'kent' },
  hidden: true
};

Arrays 數組

javascript// bad
var items = new Array();

// good
var items = [];

//使用push添加數組元素
var someStack = [];
// bad
someStack[someStack.length] = 'abracadabra';

// good
someStack.push('abracadabra');

//複製數組的最快方法
var len = items.length;
var itemsCopy = [];
var i;
// bad
for (i = 0; i < len; i++) {
  itemsCopy[i] = items[i];
}

// good
itemsCopy = items.slice();

//轉換array-like object（如：{1:'xx',2:'yy',length:2}） 成數組
var args = Array.prototype.slice.call(arguments);

Strings 字符串

javascript//使用單引號
// bad
var name = "Bob Parr";
// good
var name = 'Bob Parr';

// bad
var fullName = "Bob " + this.lastName;
// good
var fullName = 'Bob ' + this.lastName;

// 使用`＋`進行換行
var 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.';

//拼接帶標籤內容時，標籤頭尾寫一塊兒
// bad
function inbox(messages) {
  items = '

<ul>';

  for (i = 0; i < length; i++) {
    items += '<li>' + messages[i].message + '</li>';
  }

  return items + '</ul>

';
}

// good
function inbox(messages) {
  items = [];

  for (i = 0; i < length; i++) {
    items[i] = '<li>' + messages[i].message + '</li>';
  }

  return '

<ul>' + items.join('') + '</ul>

';
}

Functions 函數

javascript// 使用自執行函數
// immediately-invoked function expression (IIFE)
(function() {
  console.log('Welcome to the Internet. Please follow me.');
})();

//型參別用`arguments`
// bad
function nope(name, options, arguments) {
  // ...stuff...
}

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

Properties屬性

javascript
var luke = {
  jedi: true,
  age: 28
};

// bad
var isJedi = luke['jedi'];

//通常狀況使用`.`調用，
// good
var isJedi = luke.jedi;

function getProp(prop) {

  //屬性是變量，使用`[]`調用
  return luke[prop];
}

var isJedi = getProp('jedi');

Variables 變量

javascript
//使用var聲明變量
// bad
superPower = new SuperPower();

// good
var superPower = new SuperPower();

//不用`,`分割變量
// bad
// (compare to above, and try to spot the mistake)
var items = getItems(),
    goSportsTeam = true;
    dragonball = 'z';

// good
var items = getItems();
var goSportsTeam = true;
var dragonball = 'z';

//聲明未賦值變量在後面
// bad
var i;
var items = getItems();
var dragonball;
var goSportsTeam = true;
var len;

// good
var items = getItems();
var goSportsTeam = true;
var dragonball;
var length;
var i;

//函數內變量聲明定義儘可能放最前面，除非有函數開始有判斷`return false`，
// bad
function() {
  test();
  console.log('doing stuff..');

  //..other stuff..

  var name = getName();

  if (name === 'test') {
    return false;
  }

  return name;
}

// good
function() {
  var name = getName();

  test();
  console.log('doing stuff..');

  //..other stuff..

  if (name === 'test') {
    return false;
  }

  return name;
}

// bad
function() {
  var name = getName();

  if (!arguments.length) {
    return false;
  }

  return true;
}

// good
function() {
  if (!arguments.length) {
    return false;
  }

  var name = getName();

  return true;
}

Equality 比較操做

javascript// bad
if (name !== '') {
  // ...stuff...
}

// good
if (name) {
  // ...stuff...
}

// bad
if (collection.length > 0) {
  // ...stuff...
}

// good
if (collection.length) {
  // ...stuff...
}

Blocks 塊

javascript// bad
if (test)
  return false;

// good
if (test) return false;

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

// bad
function() { return false; }

// good
function() {
  return false;
}

Comments 註釋

javascript// 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;
}


// bad
var active = true;  // is current tab

//註釋在在代碼上方好
// good
// is current tab
var active = true;

// bad
function getType() {
  console.log('fetching type...');
  // set the default type to 'no type'
  var type = this._type || 'no type';

  return type;
}

// good
function getType() {
  console.log('fetching type...');

  //註釋上方要留一行空行
  // set the default type to 'no type'
  var type = this._type || 'no type';

  return type;
}

Type Casting 格式轉換

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';

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.
 * 經過位移的方式轉換成數字，速度會快些
 */
var val = inputValue >> 0;

var age = 0;

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

// good
var hasAge = Boolean(age);

// good
var hasAge = !!age;

Naming Conventions 命名約定

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

//名字要有語意
// good
function query() {
  // ..stuff..
}

// bad
var OBJEcttsssss = {};
var this_is_my_object = {};

//駝峯命名
// good
var thisIsMyObject = {};
function thisIsMyFunction() {}

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

//構造函數大寫
// good
function User(options) {
  this.name = options.name;
}

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

//私有屬性用`_`開頭
// good
this._firstName = 'Panda';

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

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

//保存調用者`this`爲`_this`
// good
function() {
  var _this = this;
  return function() {
    console.log(_this);
  };
}

Constructors 構造函數

javascriptfunction Jedi() {
  console.log('new jedi');
}

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

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

Events 事件

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

...

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

//傳遞id時用對象包裹後再傳
// good
$(this).trigger('listingUpdated', { listingId : listing.id });

...

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

Modules 模塊

• 說明文件路徑
• 文件名使用駝峯命名
• 開頭加上一個 `!
• 模塊中使用'use strict'嚴格模式
• 使用noConflict()無衝突的輸出

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);