Plain old JavaScript (without frameworks) holds up rather well. My simplified blackjack game from 1998 (modified in 2003) and a calendar program from 2001 (probably written before then) still work in a modern browser.
The calendar program uses document.write(), which is very embarrassing nowadays, but then again, that was what people did back in 2001.
The calendar program uses document.write(), which is very embarrassing nowadays, but then again, that was what people did back in 2001.