Is this really true? The same JavaScript I wrote 3 years ago still work, for multiple different applications. It's really uncommon that browsers break "user-space" JavaScript, I can't even remember the last heavily dependent API that got removed and cause havoc.

What does change very often is the latest trends/fads in JavaScript frameworks/UI libraries, but if you pick one and stick with it, it won't magically break because JavaScript changed. I think what's causing your problem is here is the want/need to stick with the latest flavor of frameworks/libraries instead of becoming deeply familiar with one and sticking with it.