I've swiped the build.js and watch.js from https://github.com/MakuraYami/factorio-mods I guess they got it from BarryKun ?
build zip file
node build watch a directory.
This copies the mod over to the factorio mod directory and automatically applies changes.
node watch For Windows %APPDATA%/.factorio/mods
For Linux ~/.factorio/mods
For Mac not supported