SOURCE

//数据类型判断
const demo = function(val) {
    return Object.prototype.toString.call(val)
}

var data = demo(1)
console.log(data)

class Father {
    constructor(x,y){

    }
    say(){
        console.log(11)
    }
}

class Son extends Father {
    constructor(x, y){
        super(x,y)
    }
    say(){
        console.log(super.say())
    }
    subtract(){
        console.log(this.x - this.y)
    }
}

var son = new Son(5,3)
son.subtract()