docs: function appendQueryString(url, params){
          var key;
          url = url || '';
          if(params){
              if(url.indexOf('?') === -1){
                  url += '?';
              }
              if(typeof params === 'string'){
                  url += params;
              } else if (typeof params === 'object'){
                  for(key in params){
                      if(!/[?&]$/.test(url)){
                          url += '&';
                      }
                      url += encodeURIComponent(key) + '=' + encodeURIComponent(params[key]);
                  }
              }
          }
  
          return url;
      }