That is correct, a minified JS will preserve most of the semantics of the original program.
And since the original source can come from any language, how would one know which decompiler to use.
https://github.com/jashkenas/coffeescript/wiki/List-of-langu...
Wasm was effectively an extension of asm.js. It makes the experience of compile-to-web better, but it isn't much more opaque than other projects.