adding a loaded flag to Backbone Collections via extension

gistfile1.js

/*
*= require backbone-rails
*/

 (function() {
    var _collection = Backbone.Collection;

    Backbone.Collection = function() {

        // I would like to use Backbone.Events on myself
        _.extend(this, Backbone.Events);

        // this collection is obviously not loaded
        this.loaded = false;

        // set loaded if I loaded something
        var setLoaded = _.once(function() {
            this.loaded = true;
        });

        this.bind("reset", setLoaded, this);
        this.bind("add", setLoaded, this);

        // now lets do the actual initialisation
        _collection.apply(this, arguments);
    }
    Backbone.Collection.prototype.loaded = false;
    _.extend(Backbone.Collection.prototype, _collection.prototype);
    _.extend(Backbone.Collection, _collection);

}).apply(window);