https://tailrecursion.com/~alan/micha_on_hoplon_vs_react/ is an old explanation of some of the differences that might be helpful
Is javelin usable in Clojure proper (not just ClojureScript)?
No, I don't think so
This promises to be interesting https://github.com/kennytilton/its-alive
FYI you can also use any backend - we use cljs on Node for ours