This seems to me like WebAssembly works basically like Java, but the bytecode can be compiled to from multiple languages.

Is this correct?

https://en.wikipedia.org/wiki/List_of_JVM_languages

WASM needs to move beyond MVP state and get first-class support for DOM APIs in the browser and some kind of first-class OS-agnostic APIs for outside the browser.

Until then I will be stuck with Java and J2cl/Closure (https://github.com/google/j2cl).