js中this的指向问题探讨

//直接打印
 console.log(this) //window
//function声明函数
 function bar () {conso
le.log(this)}bar() //window
//function声明函数赋给变量
 var bar = function () {console.log(this)}bar() //window
//自执行函数
 (function () {console.log(this)})(); //window

//对象方法调用
 var person = {run: function () {console.log(this)}}person.run()// person
//事件绑定
 var btn = document.querySelector("button")btn.onclick = function () {console.log(this) // btn}
//事件监听
 var btn = document.querySelector("button")btn.addEventListener('click', function () {console.log(this) //btn})
//jquery的ajax
 $.ajax({ self: this, type:"get", url: url, async:true, success: function (res) {console.log(this)
 // this指向传入$.ajxa()中的对象
 console.log(self) // window } }); 
//这里说明以下，将代码简写为$.ajax（obj） ，this指向obj,在obj中this指向window，因为在在success方法中，独享obj调用自己，所以this指向obj

//不使用new指向window
 windowfunction Person (name) {console.log(this) // window 
 this.name = name;}Person('inwe')
//使用new
 function Person (name) {this.name = name console.log(this) //people 
 self = this } var people = new Person('iwen') console.log(self === people) //true
//这里new改变了this指向，将this由window指向Person的实例对象people
new改变this指向，将this指向window改为指向person的实例people