OL3 (v3.20.0 ), draw holes on polygons. (javascript)

As ol3 have not yet implemented the "draw hole" vector functionality, I did a bit of work to achive it. So, in the meantime, my approach may help you. After the last update it works using 3.20.0 latest openlayers3 version. Propably it works with older versions as well but havent tested.

Also not that I use jsts library in order to verify whether drawn hole vertex is inside a polygon. 

Here is a demo  here(jsfiddle) (updated on 16/12/2016)

preview




It only works for simple (not multi) polygons. But you may add as many holes you like in a single polygon. It also lucks the visual hole effect during drawing (fixed with the new update).
Also prevents the draw hole ouside the selected polygon. 
I ll try to work with these and if I get something better I ll let you know.