trigger event to a widget from widget event

trigger event to a widget from widget event

I made a demo on js fiddle. The question is: I've two selectmenus widget and when happen a change on the first one I would like to trigger a new "change" event to the second selectmenu. At the moment I haven't reach that result.


I can found a workaround  with an external function but ... I would like to understand why  it doesn't work.
Thank you