code: function recoverCellIndex(rowIndex, cellIndex) {
              if (!_virtualTable[rowIndex]) {
                  return cellIndex;
              }
              if (!_virtualTable[rowIndex][cellIndex]) {
                  return cellIndex;
              }
  
              var newCellIndex = cellIndex;
              while (_virtualTable[rowIndex][newCellIndex]) {
                  newCellIndex++;
                  if (!_virtualTable[rowIndex][newCellIndex]) {
                      return newCellIndex;
                  }
              }
          }
docs: Recover free index of row to append Cell.
  
  @param {int} rowIndex Index of row to find free space.
  @param {int} cellIndex Index of cell to find free space in table.