Detailed explanation of this usage example in js_javascript skills

The examples in this article describe the usage of this in js. Share it with everyone for your reference. The details are as follows:

1. Point to window

Global variables

alert(this) //返回 [object Window]

Global function

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

2. Point to the object (in the global this points to the window, in an object this points to the object, in the closure this points to the window)

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 Window
alert(box.getThis());//the box
alert(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）

3. Use apply and call to change the this point of the function

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

4. new object

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

I hope this article will be helpful to everyone’s JavaScript programming design.