JavaScript中apply方法的用法详解与核心场景

  function A(name, age){
   this.name = name;
   this.age = age;
  }
 
  function B(name, age, time){
   A.apply(this,[name]) //这里的name必须加上[]
  }
 
  const b = new B('继承');
  console.log(b)

function Class10(){
 this.showSub = function(a,b){
    alert(a - b);
  }  
}
 
function Class11(){
 this.showAdd = function(a,b){
    alert(a + b);
  } 
}
 
function Class12(){
 Class10.apply(this);
 Class11.apply(this);  
 // Class10.call(this);
 //Class11.call(this); 
}
 
var c2 = new Class12();
c2.showSub(3,1);  //2
c2.showAdd(3,1);  //4

fn.apply(this,array)

fn.apply(this,[params1,params2,...])
//相当于
fn(params1,params2,...)//这里的this指向执行fn函数的作用域

  function C(name, age){
   console.log(this.name)
  }
 
  var name = 'windowname'
  var myObject = {name:"myA",age:"myB"};
  C.apply(myObject) //myA
  C.apply(null)//windowname
 
   function D(){
   this.name = '我是D空间'
   C.apply(this)
  }
 
  D();//我是D空间