javascript - 使用 switch 语句来识别对象实例的类型 - 不起作用

Question

我试图关注this previous question .

var Animal = function(){}

var Dog = function(){}
Dog.prototype = Object.create(Animal.prototype);

var dog = new Dog();

switch(dog.constructor){
    case Dog:
        console.log("Good Dog")
        break;
    default:
        console.log("Bad Dog");
}

它记录“Bad Dog”。

我做错了什么？

Answer 1

由于原型(prototype)继承，构造函数引用被覆盖。检查以下代码片段中的日志。

var Animal = function() {}
Animal.prototype.disp = function () {
  return 'I am an Animal';
}
var Dog = function() {}
Dog.prototype = Object.create(Animal.prototype);

var someOtherAnimal = new Dog();
// On inheriting the prototypal chain, the constructor is overridden.
console.log(someOtherAnimal.constructor === Animal);
// over riding the constructor
Dog.prototype.constructor = Dog;

var someAnimal = new Dog();
console.log(someAnimal.constructor === Dog);

switch (someAnimal.constructor) {
  case Dog:
    console.log("Good Dog")
    break;
  default:
    console.log("Bad Dog");
}
// access the animal prototpe.
console.log(someAnimal.disp());