js原型的碰到的问题

Question

    <script type="text/javascript">
        'use strict'
        function Animal(name, age){
            this.name = name
            this.age  = age
            this.say=function(){
                console.log(this)
                if (this instanceof Cat)
                    {console.log("I'm a cat.")}
                else
                    {console.log("I'm a dog")}
            }
        }
        function Cat(name, age){
            this.name= name
            this.age  = age
        }

        function Dog(name, age){
            this.name= name
            this.age  = age            
        }

        let animal = new Animal('小花', 1)
        Cat.prototype =  animal
        var cat = new Cat("喵喵", 20)
        cat.say()
        Dog.prototype =  animal
        var dog = new Dog("大黄", 2)
        dog.say()
        console.log(dog instanceof Dog)
    </script>

上述代码中，为什么调用say之后输出的都是I'm a cat,而不是I'm a cat 和I'm a dog?问题出在哪里？

Answer 1

你的2个动物类的prototype 都设置成了animal