The four call modes of the function and the this pointing to it

Type 1: Function direct execution mode

function add(a,b){
   console.log(this);
   return a+b;
  }
 add(10,20)//this===window

Type 2: Call mode of object method

var obj={
   name:'aaa',
   age:20,
   said:function(){
    console.log(this);
   }
  }
obj.said();//this===obj , here this Refers to the callee 

Type 3: The invocation mode of the constructor

function School(){
   this.said=function(){
    console.log(this);
   }
  }
var nanj=new School();
nanj.said();// Object calls its own method, this===nanj , similar to the above 

Type 4: call and apply call modes

function change(a,b){
   this.detial=a*b;
   console.log(this);
  }
  var p={};
  change.call(p,4,5);// Here this===p
  console.log(p.detial);
  var q=[];
  change.call(q,5,10)//this===q
  console.log(q.detial);
  //apply And call1 Sample usage, just apply No. 1 2 Parameters are passed in an array 
  var arr=[];
  change.apply(arr,[10,10]);//this===arr
  console.log(arr.detial);
  var str={};
  change.apply(str,[20,20]);//this===str
  console.log(str.detial);