es6的对象继承

<script type="text/javascript">
    //父类
    class P1{
        constructor(opt){
            this.x = opt.x
        }
        say(){
            console.log(this.x)
        }
    }
    class P2 extends P1{
        constructor(opt){
            super(opt)//super必须调用，这是语法规定，否则会把错
            //扩展方法
            this.y = opt.y
        }
        hi(){
            console.log(this.y)
        }
    }
    const o1 = new P1({x:0});
    const o2 = new P2({x:1,y:2});
    o1.say();//0
    o2.say();//1
    o2.hi();//2
</script>