这和原型javascript

Question

Why does alert(d.prototype) return a undefined? Shouldn't the prototyope be animaL?

function Dog(){

}
function Animal(){
    this.name = "name";
}
Dog.prototype = new Animal();
var d = new Dog();

alert(d.constructor);
alert(d.prototype);
alert(d.name);

Answer 1

The prototype property is a property of a constructor function. It's not a property of objects created with that constructor function.

Internally any object must know what its prototype is, but it's not exposed as a property with a name.

In some implementations it may be given a weird name. In Firefox it's called __proto__ , but obviously you can't rely on that working in any other browser.

http://www.packtpub.com/article/using-prototype-property-in-javascript

Answer 2

d是一个实例，用于获取原型：

d.constructor.prototype;

Answer 3

FF和chrome可以为你提供__proto__的父对象，可以使用d.__proto__来访问d.__proto__

Answer 4

I think the drawing in http://mckoss.com/jscript/object.htm describes it (I can never remember this myself). There's a property __proto__ in Firefox that references the prototype, but other than that, going from an instance to prototype isn't done (except checking with instanceof ).

Image is borrowed from above mentioned URL.

Answer 5

You shouldn't use Dog.prototype = new Animal(); Try: Dog.prototype = Animal; instead.