I also see there “Emscripten can’t run functions called with ccall”
That’s not very surprising, but not having looked into all the options, I just note WebAssembly is now supported “in all the major web browsers” (i.e. Safari, and finally Edge, but yes not IE).
It should solve the ccall problem (ang Emscripten not needed).
At least this could work for Julia only (or plus C/Python etc.) code, but I believe not still enough for JS interop (if that’s why you want to compile to use JS or its GC, Emscripten may be needed or or some workaround available to interop with JS?).