Link to a parent object

Question

I have a couple of nested objects, where A is always a part of B.

May I use the following code to access owner's properties and methods?

function A( owner ) {
  this.value = function () { return owner.value() + 1 };
}

function B() {
  this.value = function () { return 1; };
  this.a = new A( this );
}

var b = new B();
alert( b.a.value() );

Actually, it works. But I would like to know whether it is correct or not.

Answer 1

You may consider to move the methods declaration from the constructors to the prototypes of the constructors. You will save memory if you have a lot of objects A and B, because in your sample for every object there will be a copy of the method inside of it. Moving a method declaration to the prototype will allow all objects to share a single copy of this method. But you will have to keep a reference to the "owner" in A (now you use closures to keep a reference to it).

Answer 2

That's fine, at least from the implementation standpoint. Do you have any specific concerns about this approach?

Answer 3

Actually, it works. But I would like to know whether it is correct or not.

It works because you create new instance of parent and access it there:

this.a = new A( this );

The correct way (for inheritence) is to set child's prototype and constructor:

A.prototype = new B();
A.prototype.constructor = A;

For more explanation, have a look at this question.