How to Cross-Compile Java Source Code to JavaScript?

Question

Given a set of Java source code files, how can I compile them into one or more JavaScript files that can be used with hand-crafted JavaScript?

GWT is one option, but

Answer 1

While the question is about compiling Java sources to JavaScript I think it's worth mentioning that there is TeaVM which compiles Java bytecode to JavaScript. I have never tried it, but it seems very promising.