when it is safe to save()?

Also BTW is the on init function always guaranteed to run before e.g. my just restored setInterval will fire?

Yes.

Should I set E.on(init) before calling save() so it gets saved too?

If you want to run a function at boot that way rather than using onInit then yes...

After your last post I actually modified the save() docs, they're just not in the reference yet. I've also just tried to add your comments from the last post - so they now read: https://github.com/espruino/Espruino/blob/master/src/jswrap_interactive.c#L167