I know the feeling. It's not just modern stuff, I have an old ExtJS app that I dread to update. The best solution I have found is a dev / build environment in a dedicated VM that I can spin up once or twice a year to make updates. Bringing libraries up to date is a fucking nightmare and often a waste of time. For continuously updated apps I have moved away from complicated build processes. Most web apps are fine without a build process, I think there is a lot of premature optimization going on.