ClojureScript. Clojure is one of my favorite languages and my first non-trivial exposure to tools that compiled to JS happened with it (other than CoffeeScript - not a fan), so maybe I’m biased. I just can reason about things with Clojure(Script) better, it has decent interop, great React wrapper, an amazing framework and shadow-cljs <3 . YMM totally V.

OCaml translates to javascript very well. It has two ways too, bucklescript, which converts the AST to javascript and thus makes much more idiomatic and readable javascript, or js_of_ocaml (jsoo), which converts the bytecode to javascript, can often be a little bit faster than bucklescript in some cases but mostly on par, however it doesn’t require the source where bucklescript does require the source, so jsoo is more ‘generically’ useful, though it does output very very low level unreadable javascript. ^.^;

Emscripten has been my main thing that’s converted to javascript to date, but nothing ‘in production’ with it, wasm is better now anyway for those kinds of things.

Purescript sounds interesting too though, but not tried it yet.

Currently Svelte.