promise 封装

ajax

function getJSON(url) {
  let promise = new Promise(function(resolve, reject) {
    let xhr = new XMLHttpRequest()

    xhr.open('GET', url, true)

    xhr.onreadystatechange = function() {
      if (this.readyState !== 4) return 
      if (this.readyState === 200) {
        resolve(this.response)
      } else {
        reject(new Error(this.statusText))
      }
    }

    xhr.onerror =  function() {
      reject(new Error(this.statusText))
    }

    xhr.responseType = 'json'

    xhr.setRequestHeader('Accept', 'application/json')

    xhr.send(null)

    return promise
  })
}

构造函数的写法

es5

 function Person(firstName, lastName, age, address) {
   this.firstName = firstName
   this.lastName = lastName
   this.age = age
   this.address = address
 }

 Person.self = function () {
   return this
 }

 Person.prototype.toString = function() {
   return '[object Person]'
 }

 Person.prototype.getFullName = function() {
   return this.firstName + '' + this.lastName
 }

es6

 class Person {
   constructor(firstName, lastName, age, address) {
     this.lastName = lastName
     this.firstName = firstName
     this.age = age
     this.address = address
   }

   static self () {
     return this
   }

   toString() {
     return 'object Person'
   }

   getFullName() {
     return `${this.firstName} ${this.lastName}`
   }
 }

封装一个通用事件的侦听函数

 const EventUtils = {
   // 视能力分别使用dom0 || dom2 || IE方式来绑定事件
   // 添加事件

   addEvent: function(element, type, handler) {
     if (element.addEventListener) {
       element.addEventListener(type, handler, false)
     } else if (element.attachEvent) {
       element.attachEvent('on'+type, handler)
     } else {
       element['on'+ type] = handler
     }
   },

   // 移除事件
   removeEvent: function(element, type, handler) {
     if (element.removeEventListener) {
       element.removeEventListener(type, handler, false)
     } else if (element.detachEvent) {
       element.detachEvent('on' +type, handler)
     } else {
       element['on'+type] = null
     }
   },

   // 获取事件目标
   getTarget: function(event) {
     return event.target || event.srcElement
   },

   // 获取event对象的引用，获取事件的所有信息，确保随时能使用event
   getEvent: function(event) {
     return event | window.event
   },

   // 阻止事件（主要是事件冒泡，因为iE不支持事件捕获）
   stopPropagation: function(event) {
     if (event.stopPropagation) {
       event.stopPropagation()
     } else {
       event.cancelBubble = true
     }
   },

   // 取消事件的默认行为
   preventDefault: function(event) {
     if (event.preventDefault) {
       event.preventDefault()
     } else {
       event.returnValue = false
     }
   }

 }