Prosemirror-Table splitting a cell

SplitCell.js

function splitCellVertically(state, dispatch) {
  if (!isInTable(state)) { return false }
  const rect = selectedRect(state);
  const selectionWidth  = rect.right - rect.left
  const selectionHeight = rect.bottom - rect.top
  if (selectionWidth > 1 || selectionHeight > 1) {return false}
  if (dispatch) {
    const tr = state.tr
    const ref = rect
    const row = rect.bottom
    var map = ref.map;
    var tableStart = ref.tableStart;
    var table = ref.table;

    const $selectedCell = selectionCell(state)
    const selectedCellNode = state.doc.nodeAt($selectedCell.pos)
    const fragmentAfterCursor = selectedCellNode.cut(
      state.selection.head - $selectedCell.pos - 1
    ).content

    var rowPos = tableStart;
    for (var i = 0; i < row; i++) { rowPos += table.child(i).nodeSize; }
    var newCell, refRow = row > 0 ? -1 : 0;
    if (rowIsHeader(map, table, row + refRow))
      { refRow = row == 0 || row == map.height ? null : 0; }
    for (var col = 0, index = map.width * row; col < map.width; col++, index++) {
      // Is current column
      if (col == rect.left) {
        // create new cell
        var type = refRow == null ? tableNodeTypes(table.type.schema).cell
            : table.nodeAt(map.map[index + refRow * map.width]).type;
        newCell = type.createAndFill(null, fragmentAfterCursor);
      } else {
        // increase rowSpan
        var pos = map.map[index - map.width], attrs = table.nodeAt(pos).attrs;
        tr.setNodeMarkup(tableStart + pos, null, setAttr(attrs, "rowspan", attrs.rowspan + 1));
        col += attrs.colspan - 1;
      }
    }
    tr.insert(rowPos, tableNodeTypes(table.type.schema).row.create(null, newCell));
    tr.delete(state.selection.head, $selectedCell.pos + selectedCellNode.nodeSize)

    dispatch(tr);
  }
  return true
}