[ricardobeat]

To cut the story short, there is basically a single way to do "proper" inheritance in javascript, which is Crockford's prototypal inheritance [1]. There are a dozen variations on it, here is one:

    function inherits (child, parent) {
        extend(child, parent)
        function Ctor () { this.constructor = child }
        Ctor.prototype = parent.prototype
        child.prototype = new Ctor()
        child.__super__ = parent.prototype
        return child
    }

    function Animal ...
    Animal.prototype.x = ...

    function Cat ...
 
    inherits(Cat, Animal)

See Backbone's implementation [2] for another example. This eventually morphed into the standard `Object.create` method [3], supported in IE9+.

[1] http://javascript.crockford.com/prototypal.html

[2] http://backbonejs.org/docs/backbone.html#section-186

[3] https://developer.mozilla.org/en-US/docs/JavaScript/Referenc...