Question

I’m currently trying to test whether it’s possible to make one object inherit from another object AFTER both objects have been created using literals. I tried to aim the constructors and prototypes at one another but it seems like no matter what, the only way Im going to pull this off is by building a new object using one of the pre-existing ones.. Let me know if I’m wrong. Here was my quick attempt to solve the problem.

Object.relate = function(parent, child){
    function F(){};
    F.prototype = parent;
    child.constructor = F;
}
alpha = {a:1};
beta = {b:2};

Object.relate(alpha, beta); 

Answer 1

In your code beta can access properties defined on alpha by using beta.constructor.prototype.

When you use new on a function like

var obj = new F();

then obj.__proto__ is automatically set to F.prototype. When you have already existing objects and you are not creating the object using new you must set the __proto__ by yourself.

obj.__proto__ = F.prototype;

So in your example you need to call

child.__proto__ = parent;

Resources:

• https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Object/proto
• http://killdream.github.com//blog/2011/10/understanding-javascript-oop/index.html#sec-4-1

The problem is that now every browser expose the __proto__ property. IE doesn’t support it so you cannot create a browser-compatible solution without actually creating a new object and copying the properties.