SOURCE

function Parent(name, age){
    this.name = name;
    this.age = age;
    this.play = function() {
        console.log("play");
    }
}

Parent.prototype.say = function() {
    console.log(this.name);
    console.log(this.age);
}

function Child(){}
Child.prototype = new Parent();
Child.prototype.constructor = Child;
Child.prototype.name = 'fangsong';
Child.prototype.age = 19;

const child = new Child();
child.say()
child.play();