//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()