Detailed explanation of this usage example in js

This example describes the usage of this in js. Share it for your reference. The details are as follows:

1. Point to window

Global variables

alert(this) //Return [object Window]

Global functions

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

2. Point to the object (in the global world this points to window, in a certain object this points to the object, in the closure this point to window)

var user="the Window";
var box={
  user:'the box',
  getThis:function(){
    return ;
  },
  getThis2:function(){
    return function (){
      return ;
    }
  }
};
alert();//the Window
alert(());//the box
alert(box.getThis2()());
//the Window (because of using closures, this point to window here)alert(box.getThis2().call(box));
//the box Object impersonation（HerethisPoint toboxObject）

3. Use apply, call to change the function's this pointer

function sum(num1, num2){
  return num1+num2;
}
function box(num1, num2){
  return (this, [num1, num2]);
  //this indicates the scope of window. The box impersonates sum to execute}
(box(10,10)); //20

4. new object

function Person(){
   (this) //Point this to a newly created empty object}
var p = new Person();

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