code: function (url, force) {
              if (force || this._timestampURL[url]) {
                  var timestamp = (new Date()).getTime();
                  if (url.indexOf("?") != -1) {
                      return url + "&timestamp=" + timestamp;
                  } else {
                      return url + "?timestamp=" + timestamp;
                  }
              } else {
                  return url;
              }
          }
docs: Add a timestamp to the given URL if it should bypass browser cache.
  @param {String} url URL for which a timestamp should be added if necessary
  @param {Boolean} force if true, the timestamp will always be added
  @return {String} URL with the added timestamp if this is required