Hi there.
I tried your project on my Moto G running KitKat and it works with no problems.
The javascript gets executed in both Release and Debug(legacy) modes.
In Debug (rapid) mode the WebViews fail to find the file
web_view_extras_demo.htm so nothing works.
That's not a bug in the code, just a side effect of using rapid debug mode, read more here:
https://www.b4x.com/android/forum/pages/results/?query=rapid debug file not found&page=1&prefix=0.
I've updated your project to use a WebChromeClient and that all works with no problems too.
So i'm not sure what to suggest.
What device and what version of android are you using to run your project?