Bangle board name defines to a file

is build_jswrapper and build_jswrapper_efficient. Doing the same thing just one is build for speed?

Yes - actually I think build_jswrapper_efficient should be removed (I've just got rid of it now) - the last update of note was 10 years ago, and I think at the start of Espruino I'd hoped I could make something that was a bit faster than the current solution (but it never actually worked)