Comment by kethinov

Vanilla JS is very powerful and has the features you need to build SPAs without a big framework. Proxies and mutation observers are great for maintaining state, Updating the DOM yourself is fine, view transitions are awesome, etc. The only thing that's hard is routing, but there are lots of small dedicated JS libraries to handle that. Here's one I made that gives you the Express API on the frontend: https://github.com/rooseveltframework/single-page-express