It works reasonably well for me so long as I have done all the development first using a browser, then when that works flawlessly I move it over to Shotcut. Shotcut is definitely not the best platform to debug Javascript, though using my framework you don’t have to do that, just modify the CSS and HTML.
There are still a few niggles with making minor changes to the Overlay HTML filters (but mainly when I’m modifying the Javascript) then RELOADING the new version of the filter. It generally works, but I find it best to save the .mlt file then close the file and re-open the .mlt file having changed the HTML/CSS.
Jonray has been making good use of the framework I’ve developed, see:
and other posts he’s made.
and if you go to my website: Shotcut - Elusien's Contributions you’ll see some of the things I’ve done for testing the framework.