2.extends继承

super关键字

tips:子类会自动继承父类的方法
在继承的构造函数中super必须放在第一行

    class Father{
          constructor(x,y){
              this.x=x;
              this.y=y;
          }
          count(x,y){
            console.log(x+y);
          }
      } 
    class Son extends Father{
        constructor(x,y){
          //在继承的构造函数中super必须放在第一行
            super(x,y);
        }
    }
  var son=new Son();
son.count(2,4)

demo

     class   Person{
         constructor(name,age){
            this.name=name;
            this.age=age
         }
         sayName(){
             console.log(this.name);
         }
     }
     class Student extends Person{
         constructor(name,age,skill){
              super(name,age);
               this.skill=skill;
         }
     }
      var s=new Student("李思",19,"wechat")
      s.sayName()
      console.log(s);