js中this用法实例详解

alert(this) //返回 [object Window]

function sayHello(){  alert(this);}sayHello();

var user="the Window";var box={  user:'the box',  getThis:function(){    return this.user;  },  getThis2:function(){    return function (){      return this.user;    }  }};alert(this.user);//the Windowalert(box.getThis());//the boxalert(box.getThis2()());//the Window （由于使用了闭包，这里的this指向window）alert(box.getThis2().call(box));//the box 对象冒充（这里的this指向box对象）

function sum(num1, num2){  return num1+num2;}function box(num1, num2){  return sum.apply(this, [num1, num2]);  //this 表示window的作用域 box冒充sum来执行}console.log(box(10,10)); //20

function Person(){   console.log(this) //将 this 指向一个新建的空对象}var p = new Person();