code: function () {
        //data fetching logic
        fetchData().then(
          function (result) {
            handleNewData(result.data);
          },
          function (errorResponse) {
            if (errorHandler) {
              errorHandler(self.name, lang, errorResponse).then(handleNewData, rejectDeferredWithPartName);
            } else {
              rejectDeferredWithPartName();
            }
          });
      }
docs: private helper