Best way to modify a variable with out storage

Yes, save() will save the state of the program, but it'll also re-run onInit(), so you'd have to take account of that somehow.

EEPROMs are probably the most sensible solution (the OneWire ones are quite easy to work with as well) . Other options are:

• to use an SD card (obviously it's built into the normal Espruino Board, but you'd have to wire it up)
  
• to use the STM32F1Flash module to access Espruino's flash memory directly and save all your information to your own page. Again, that won't work for you though because you're using the F4