/public/js/collections/todos.js

define([
    'underscore',
    'backbone',
    'libs/backbone/localstorage',
    'models/todo'
], function (_, Backbone, Store, Todo) {

    var TodosCollection = Backbone.Collection.extend({

        // Reference to this collection's model.
        model:Todo,

        url:'/todos',

        // Filter down the list of all todo items that are finished.
        done:function () {
            return this.filter(function (todo) {
                return todo.get('done');
            });
        },

        // Filter down the list to only todo items that are still not finished.
        remaining:function () {
            return this.without.apply(this, this.done());
        },

        // We keep the Todos in sequential order, despite being saved by unordered
        // GUID in the database. This generates the next order number for new items.
        nextOrder:function () {
            if (!this.length) return 1;
            return this.last().get('order') + 1;
        },

        // Todos are sorted by their original insertion order.
        comparator:function (todo) {
            return todo.get('order');
        }
    });
    return new TodosCollection;
});