语言特性

name = 'MyName'

var name = 'MyName'

/* globals jQuery */
var element = jQuery('#element-id')

var hangModules = [],
  missModules = [],
  visited = {}

var hangModules = []
var missModules = []
var visited = {}

function kv2List(source) {
  var list = []
  var key
  var item

  for (key in source) {
    if (source.hasOwnProperty(key)) {
      item = {
        k: key,
        v: source[key],
      }

      list.push(item)
    }
  }

  return list
}

function kv2List(source) {
  var list = []

  for (var key in source) {
    if (source.hasOwnProperty(key)) {
      var item = {
        k: key,
        v: source[key],
      }

      list.push(item)
    }
  }

  return list
}

if (age == 30) {
  // ......
}

if (age === 30) {
  // ......
}

// 字符串为空
if (name === '') {
  // ......
}

// 字符串为空
if (!name) {
  // ......
}

// 字符串非空
if (name !== '') {
  // ......
}

// 字符串非空
if (name) {
  // ......
}

// 数组非空
if (collection.length > 0) {
  // ......
}

// 数组非空
if (collection.length) {
  // ......
}

// 布尔不成立
if (notTrue === false) {
  // ......
}

// 布尔不成立
if (!notTrue) {
  // ......
}

// null 或 undefined
if (noValue === null || typeof noValue === 'undefined') {
  // ......
}

// 布尔不成立
if (noValue == null) {
  // ......
}

var type = typeof variable
if (type === 'object') {
  // ......
} else if (type === 'number' || type === 'boolean' || type === 'string') {
  // ......
}

switch (typeof variable) {
  case 'object':
    // ......
    break
  case 'number':
  case 'boolean':
  case 'string':
    // ......
    break
}

function getName() {
  if (name) {
    return name
  } else {
    return 'unnamed'
  }
}

function getName() {
  if (name) {
    return name
  }

  return 'unnamed'
}

for (var i = 0, len = elements.length; i < len; i++) {
  var element = elements[i]
  addListener(element, 'click', function () {})
}

function clicker() {
  // ......
}

for (var i = 0, len = elements.length; i < len; i++) {
  var element = elements[i]
  addListener(element, 'click', clicker)
}

for (var i = 0, len = elements.length; i < len; i++) {
  var element = elements[i]
  element.style.width = wrap.offsetWidth + 'px'
  // ......
}

var width = wrap.offsetWidth + 'px'
for (var i = 0, len = elements.length; i < len; i++) {
  var element = elements[i]
  element.style.width = width
  // ......
}

for (var i = 0, len = elements.length; i < len; i++) {
  var element = elements[i]
  // ......
}

var len = elements.length
while (len--) {
  var element = elements[len]
  // ......
}

// string
typeof variable === 'string'

// number
typeof variable === 'number'

// boolean
typeof variable === 'boolean'

// Function
typeof variable === 'function'

// Object
typeof variable === 'object'

// RegExp
variable instanceof RegExp

// Array
variable instanceof Array

// null
variable === null

// null or undefined
variable == null

// undefined
typeof variable === 'undefined'

new String(num)
num.toString()
String(num)

num + ''

Number(str)

;+str

var width = '200px'
parseInt(width, 10)

parseInt(str)

parseInt(str, 10)

var num = 3.14
!!num

var num = 3.14
parseInt(num, 10)

var num = 3.14
Math.ceil(num)

var obj = new Object()

var obj = {}

var info = {
  name: 'someone',
  age: 28,
}

var info = {
  name: 'someone',
  age: 28,
  'more-info': '...',
}

var info = {
  name: 'someone',
  age: 28,
  'more-info': '...',
}

// 以下行为绝对禁止
String.prototype.trim = function () {}

info.age
info['more-info']

var newInfo = {}
for (var key in info) {
  if (info.hasOwnProperty(key)) {
    newInfo[key] = info[key]
  }
}

var arr = new Array()

var arr = []

var arr = ['a', 'b', 'c']

// 这里仅作演示, 实际中应使用 Object 类型
arr.other = 'other things'

// 正确的遍历方式
for (var i = 0, len = arr.length; i < len; i++) {
  console.log(i)
}

// 错误的遍历方式
for (var i in arr) {
  console.log(i)
}

function syncViewStateOnUserAction() {
  if (x.checked) {
    y.checked = true
    z.value = ''
  } else {
    y.checked = false
  }

  if (a.value) {
    warning.innerText = ''
    submitButton.disabled = false
  } else {
    warning.innerText = 'Please enter it'
    submitButton.disabled = true
  }
}

function syncViewStateOnUserAction() {
  syncXStateToView()
  checkAAvailability()
}

function syncXStateToView() {
  y.checked = x.checked

  if (x.checked) {
    z.value = ''
  }
}

function checkAAvailability() {
  if (a.value) {
    clearWarnignForA()
  } else {
    displayWarningForAMissing()
  }
}

/**
 * 移除某个元素
 *
 * @param {Node} element 需要移除的元素
 * @param {boolean} removeEventListeners 是否同时将所有注册在元素上的事件移除
 */
function removeElement(element, removeEventListeners) {
  element.parent.removeChild(element)

  if (removeEventListeners) {
    element.clearEventListeners()
  }
}

/**
 * 移除某个元素
 *
 * @param {Node} element 需要移除的元素
 * @param {Object} options 相关的逻辑配置
 * @param {boolean} options.removeEventListeners 是否同时将所有注册在元素上的事件移除
 */
function removeElement(element, options) {
  element.parent.removeChild(element)

  if (options.removeEventListeners) {
    element.clearEventListeners()
  }
}

var tasks = []
for (var i = 0; i < 5; i++) {
  tasks[tasks.length] = function () {
    console.log('Current cursor is at ' + i)
  }
}

var len = tasks.length
while (len--) {
  tasks[len]()
}

var tasks = []
for (var i = 0; i < 5; i++) {
  // 注意有一层额外的闭包
  tasks[tasks.length] = (function (i) {
    return function () {
      console.log('Current cursor is at ' + i)
    }
  })(i)
}

var len = tasks.length
while (len--) {
  tasks[len]()
}

var emptyFunction = function () {}

var EMPTY_FUNCTION = function () {}

function MyClass() {}

MyClass.prototype.abstractMethod = EMPTY_FUNCTION
MyClass.prototype.before = EMPTY_FUNCTION
MyClass.prototype.after = EMPTY_FUNCTION

/**
 * 构建类之间的继承关系
 *
 * @param {Function} subClass 子类函数
 * @param {Function} superClass 父类函数
 */
function inherits(subClass, superClass) {
  var F = new Function()
  F.prototype = superClass.prototype
  subClass.prototype = new F()
  subClass.prototype.constructor = subClass
}

function Animal(name) {
  this.name = name
}

// 直接prototype等于对象时，需要修正constructor
Animal.prototype = {
  constructor: Animal,

  jump: function () {
    alert('animal ' + this.name + ' jump')
  },
}

// 这种方式扩展prototype则无需理会constructor
Animal.prototype.jump = function () {
  alert('animal ' + this.name + ' jump')
}

function TextNode(value, engine) {
  this.value = value
  this.engine = engine
}

TextNode.prototype.clone = function () {
  return this
}

var handler = new Function('x', 'y', 'return x + y;')
var result = handler($('#x').val(), $('#y').val())

try {
  delete o.x
} catch (deleteError) {
  o.x = null
}

function Tree(datasource) {
  this.datasource = datasource
}

Tree.prototype.selectNode = function (id) {
  // 从datasource中找出节点对象
  var node = this.findNode(id)
  if (node) {
    node.selected = true
    this.flushView()
  }
}

function Tree(datasource) {
  this.datasource = datasource
  this.selectedNodeIndex = {}
}

Tree.prototype.selectNode = function (id) {
  // 从datasource中找出节点对象
  var node = this.findNode(id)

  if (node) {
    this.selectedNodeIndex[id] = true
    this.flushView()
  }
}