code: function(url, constructReceiver, user_callback) {
      var id = 'a' + utils.random_string(6);
      var url_id = url + '?c=' + escape(WPrefix + '.' + id);
      // Callback will be called exactly once.
      var callback = function(frame) {
          delete _window[WPrefix][id];
          user_callback(frame);
      };
  
      var close_script = constructReceiver(url_id, callback);
      _window[WPrefix][id] = close_script;
      var stop = function() {
          if (_window[WPrefix][id]) {
              _window[WPrefix][id](utils.closeFrame(1000, "JSONP user aborted read"));
          }
      };
      return stop;
  }
docs: Abstract away code that handles global namespace pollution.