在构造函数变量上定义对象时，JavaScript中会发生什么

Question

Say I have defined a Constructor and a prototype in Javascript like this:

MyGame.Player = function(){
    this.somevar = 42;
};
MyGame.Player.prototype = {
    somevar: null,
    someFunc: function(){}
};

What will happen if I do the following:

MyGame.Player.Helper = function(){...}
MyGame.Player.Helper.prototype = {...}

• Will javascript allow this actually?
• Will the Helper appear as ownProperty in an instance of MyGame.Player() ?
• Can I always create new Helper objects even if I don't have a Player object?

Answer 1

Will javascript allow this actually?

Sure. It's just a function as property of an object. In classical OOP this would be called a class method .

Will the Helper appear as ownProperty in an instance of MyGame.Player()?

Nope. It's a property of the constructor function , not of the instance. The instance only gets all properties assigned to this in the constructor and anything from the prototype . It doesn't inherit properties of the constructor function.

Can I always create new Helper objects even if I don't have a Player object?

Sure, because you call new MyGame.Player.Helper , not new (new MyGame.Player).Helper .

Put another way, you just assigned a function to MyGame.Player.Helper , of course you can call it via MyGame.Player.Helper() , because that's where you just put it.