There is a certain irony to this. Framework heavy Javascript will be hard to rebuild, even, after 1-2 years (NPM churn). Vanilla JS? Decades. I think you can run a JS script from 1998 without any issues.

Modern Vanilla JS written in 2018 has the same backwards compatibility guarantees, it's extremely likely that you'll be able to run it in 2038.

Once you add Babel, React & co, all bets are off...