Following the firebase function getting started guide and getting a seemingly simple error once trying to deploy with:
firebase deploy --only functions
i d
As an extra doing npm --prefix %RESOURCE_DIR% run lint like @Deji James said, made me some progress but still didn't work.
As a suggestion I found this https://github.com/firebase/firebase-tools/issues/610
and @merlinnot says here Hey guys, you all probably have sth in your predeploy in firebase.json, don't you? Just delete what you have there for now if it's not that important.
worked for me. PS. before deciding to delete, I have done all reinstall things, uninstall things. Only this is worked.