I've used Tampermonkey for a couple of moderately complex things and it does work well... I didn't come across a particularly nice way to use an external editor or integrate it with a normal dev workflow though, I wonder if anyone has tricks to share?
I'm fairly satisfied with editing in VS Code, using a tsconfig.json with strict mode and checkJs turned on, then using JSDoc for typing. The ugly bit is the manual copy-paste into the Tampermonkey code area each time.
