transport.js

    var Transport = function(methods) {
        var fn = function(options) {
            this.options = options || {};
        };
        _.extend(fn.prototype, Transport.prototype, methods);
        return fn;
    };
    _.extend(Transport.prototype, Backbone.Events, {
        // stub
        validate: function(parsed) { return true; },
        parse: function(data) {
            var parsed;
            // parse the data, we have JSON and regular HTML undistinguished here
            try {
                parsed = JSON.parse(data);
            } catch (e) {
                // can't parse as JSON - treat it as raw html string
                parsed = { html: data };
            }
            return parsed;
        },
        request: function(options) {
            options = options || {};

            var dfd = _.Deferred();

            if (this.options.success) dfd.done(this.options.success);
            if (this.options.failure) dfd.fail(this.options.failure);

            // make sure we don't send shit along the way,
            // it breaks advertisier's CORS
            $.ajaxSettings.beforeSend = function(xhr) {
                xhr.withCredentials = false;
            };

            var context = this.options.context || this;
            $.ajax({
                url: options.url,
                context: this,

                success: function(data) {
                    var parsed = this.parse(data);

                    if ( this.validate(parsed) ) {
                        dfd.resolveWith(context, [parsed, options]);
                    } else {
                        dfd.rejectWith(context, ['No data received', options.url]);
                    }
                },
                error: function(status, xhr, settings) {
                    dfd.rejectWith(context, [status, options.url]);
                }
            });

            return dfd;
        }
    });

    var AdTransport = Transport({
        validate: function(parsed) {
            return !!(parsed.html || parsed.url && (parsed.img.src || parsed.img.src_alt));
        }
    });