Bake JavaScript into firmware

As @Wilberforce says, I'd suggest just getting it working, using save() or E.setBootCode(), then reading out the complete contents flash memory. You can then write that to any new devices - of course how you do that depends on the device you're using :)

If you're compiling yourself you can compile in JS code to get executed pretty easily too, but it's realistically more painful than just reading what's in flash memory