A long time ago, before the ocsigen project gave us the js_of_ocaml compiler, they gave obrowser (paper) which is an OCaml bytecode interpreter written in JavaScript.
I know there are various project to compile OCaml directly to wasm, but out of sheer curiosity, I wonder if someone has taken the bytecode path.
There is wasicaml.
Also, it looks like OCamlPro have been working on something called “wasocaml” which they presented to the WebAssembly Garbage Collection Subgroup in January. There are slides and notes from their presentation. According to the slides, it looks like it uses an Flambda to Wasm compilation strategy.