How can I modify the polyline to bezier line

in this below demo, I want to modify the polyline to bezier line, How to implement it ?

http://gojs.net/latest/extensions/PolygonDrawing.html
Thanks.

Did you try setting PolygonDrawingTool.hasArcs to true?

Note, that just supports drawing quadratic bezier curves – if you really want cubic bezier curves, you’ll need to adapt the PolygonDrawingTool yourself.

it works .thanks you very much!! use chinese 谢谢!