Extending the defaults of a Model superclass in Backbone.js

The problem is that Inventory.prototype.defaults and Extended.prototype.defaults has the same reference, because you have not override the reference.

So you can do this in 2 ways, maybe more but i only found this 2:

Edit: The first example is incorrect (see comments); please refer to the second.

var ExtendedInventory = Inventory.extend({
    defaults: {
        rabit:25
    }
});

_.extend(ExtendedInventory.prototype.defaults, Inventory.prototype.defaults);

or

var ExtendedInventory = Inventory.extend({
    defaults: _.extend({},Inventory.prototype.defaults,
         {rabit:25}
    )
});

I think the first looks cleaner.