code: function (url, onDone) {
  
      SR.Log('url to get: ' + url);
      
      var xmlHttp = new XMLHttpRequest(); 
      
      // set callback when response is returned
  	// returns 'undefined' if no response or request failed
      xmlHttp.onreadystatechange = onHttpResponse(xmlHttp, onDone);
      xmlHttp.open("GET", url, true);
      xmlHttp.send(null);
  }
docs: async version