OK, now I found out the root of half of the problem

Why my application did not work on Jolla; the problem was not my javascript, it was actually one of the JSON files I use for configuration... in the latest commit I modified the file format but when I pulled the new version from git to my device I forgot to update the file-in-use to the new template

But the original question remains; Where do I see the web console output from the browser???