class

class Animal{
        constructor(x,y){
            this.x=x
            this.y=y
        }
        sum(){
            return this.x+this.y
        }
    }
    class Human extends Animal{
        constructor(x,y,z){
            super(x,y)  //继承父类的this
            this.z=z
        }
        sum(){
            return this.z+super.sum() //调用父类的this
        }
    }

    let person=new Human(2,3,3)