Lazy-loading TreeGrid

In the tree grid below, collapsed nodes have a single dummy child. When a node is expanded, more nodes are loaded on demand.

This is a common pattern known as 'lazy-loading'.

  // create the grid
  var theGrid = new wijmo.grid.FlexGrid('#theGrid', {
    childItemsPath: 'children',
    headersVisibility: 'Column',
    groupCollapsedChanged: groupCollapsedChanged,
    autoGenerateColumns: false,
    columns: [{
        binding: 'name',
        header: 'Customer Name',
        width: '*'
      },
      {
        binding: 'id',
        header: 'ID',
        align: 'center',
        cssClass: 'id-column'
      }
    ],
    itemsSource: getData(),
  });

  // start collapsed
  theGrid.collapseGroupsToLevel(0);

  // update row when items are loaded
  function updateRowCount(grid) {
    document.getElementById('rowCount').textContent = wijmo.Globalize.format(grid.rows.length, 'n0');
  }
  updateRowCount(theGrid);

  // load data when collapse node is expanded
  function groupCollapsedChanged(s, e) {
    var row = s.rows[e.row],
      item = row.dataItem;

    // did we just expand a node with a dummy child?
    if (!row.isCollapsed &&
      item.children.length == 1 &&
      item.children[0].name == '') {

      // can't lazy load while updating rows
      if (s.rows.isUpdating) {
        row.isCollapsed = true;
        return;
      }

      // replace the dummy child with actual nodes
      item.children.length = 0;
      var cnt = Math.round(Math.random() * 5) + 1;
      for (var i = 0; i < cnt; i++) {
        var node = createNode();
        item.children.push(node);
      }

      // refresh the view
      s.collectionView.refresh();

      // collapse the new item's child items
      for (var i = row.index + 1; i < s.rows.length; i++) {
        var childRow = s.rows[i];
        if (childRow.level <= row.level) {
          break;
        }
        childRow.isCollapsed = true;
      }

      // update row count
      updateRowCount(s);
    }
  }

  // create/retrieve data
  function getData() {
    var tree = [];
    tree.push(createNode());
    tree.push(createNode());
    return tree;
  }
  var nodeId;

  function createNode(dummy) {
    var first = 'Al,Bob,Cal,Dan,Ed,Fred,Greg,Hal,Ian,Jack,Karl,Lou,Moe,Nate,Oleg,Paul,Quincy,Rod,Sue,Uwe,Vic,Walt,Xiu,Yuri,Zack'.split(','),
      last = 'Adams,Baum,Cole,Dell,Evans,Fell,Green,Hill,Isman,Jones,Krup,Lee,Monk,Nye,Opus,Pitt,Quaid,Riems,Stark,Trell,Unger,Voss,Wang,Xie,Zalm'.split(','),
      name = dummy ? '' : getOneOf(first) + ' ' + getOneOf(last),
      children = [];
    if (!dummy) {
      children.push(createNode(true));
    }
    if (nodeId == null) nodeId = 0;
    return {
      id: nodeId++,
      name: name,
      children: children
    };
  }

  function getOneOf(arr) {
    return arr[Math.floor(Math.random() * arr.length)];
  }