Otherwise it'd be up to someone to use emscripten to convert the existing C code to JS. For someone with a little experience with it, it should just be a few minutes work.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
The output isn't encoded at all, past what heatshrink provides.
I doubt lxbase62 would do it, but there is https://www.npmjs.com/package/heatshrinkÂ-ts which might help you?
Otherwise it'd be up to someone to use emscripten to convert the existing C code to JS. For someone with a little experience with it, it should just be a few minutes work.