这样的状态oop好奇怪呀....

function makeClass(name) {
  var Obj = class {
    constructor(id) {
      this.id = id
    }
    say(msg) {
      console.log(name + ">" + this.id + ":" + msg)
    }
  }
  return Obj
}
var Animal = makeClass("Animal")
var Bird = makeClass("Bird")
var bird = new Bird("1")
bird.say("hello ")
var animal = new Animal("2")
animal.say("你好")
animal.say = bird.say
animal.say("你好,代替")