edx-platform/cms/static/js/collections/textbook.js

define(['backbone', 'js/models/textbook'],
        function(Backbone, TextbookModel) {
            var TextbookCollection = Backbone.Collection.extend({
                model: TextbookModel,
                url: function() { return CMS.URL.TEXTBOOKS; }
            });
            return TextbookCollection;
        });