code: function cssPoll() {
          for (var url in monitors) {
              var callbackObj = monitors[url],
                  node = callbackObj.node;
              if (isCssLoaded(node, url)) {
                  if (callbackObj.callback) {
                      callbackObj.callback.call(node);
                  }
                  delete monitors[url];
              }
          }
  
          if (Utils.isEmptyObject(monitors)) {
              logger.debug('clear css poll timer');
              timer = 0;
          } else {
              timer = setTimeout(cssPoll, CSS_POLL_INTERVAL);
          }
      }
docs: single thread is ok