code: function () {
                              hints = hints || {};
                              var itemPromise = (
                                  typeof hints.groupMemberKey === "string" && that._listBinding.fromKey ?
                                      that._listBinding.fromKey(hints.groupMemberKey) :
                                  typeof hints.groupMemberIndex === "number" && that._listBinding.fromIndex ?
                                      that._listBinding.fromIndex(hints.groupMemberIndex) :
                                  hints.groupMemberDescription !== undefined && that._listBinding.fromDescription ?
                                      that._listBinding.fromDescription(hints.groupMemberDescription) :
                                      that._listBinding.first()
                              );
  
                              var fetchBefore = Math.floor(0.5 * (that._batchSize - 1));
                              that._fetchBatch(itemPromise, fetchBefore, that._batchSize - 1 - fetchBefore);
                          }
docs: fetchInitialBatch