docs: function requestData() {
      let visible = Math.ceil(_(this).parent.offsetHeight / _(this).itemHeight);
      let scrollIndex = Math.floor(_(this).view.scrollbar.scrollTop / _(this).itemHeight);
      let request = buildRequest.call(this, scrollIndex, visible);
      _(this).request = request;
      _(this).onDataFetch(request, setData.bind(this));
  }