While Loop or setWatch?

Since Espruino does not support interrupt directly and setWatch callback only executes in main loop, I only see only option to setup the IRQ option in setWatch

Realistically the vast majority of hardware is absolutely fine waiting a little while after asserting the IRQ line - you don't generally need to jump in and do stuff immediately, and executing in the main loop is fine.

Having said that, generally when I'm writing modules, if I'm only expecting to wait for a few milliseconds (eg. ~10ms) then I'll just add a while (pin.read()); as you suggest (ideally with a timeout - so var timeout=100;while (--timeout && pin.read());).

If it's more than 10ms I'd use setWatch though