toOptionsJSON method
Implementation
@override
void toOptionsJSON(StringBuffer buffer) {
  super.toOptionsJSON(buffer);
  if (draggableEnd != null) {
    buffer.writeAll(['"draggableEnd":', draggableEnd, ','], '');
  }
  if (draggableStart != null) {
    buffer.writeAll(['"draggableStart":', draggableStart, ','], '');
  }
  if (draggableX1 != null) {
    buffer.writeAll(['"draggableX1":', draggableX1, ','], '');
  }
  if (draggableX2 != null) {
    buffer.writeAll(['"draggableX2":', draggableX2, ','], '');
  }
}