No, but there are tons of prettifiers that can get minified/obfuscated JS back into a state that it can be read and reasoned about fairly easily. It's not like minifiying/obfuscating JS compiles it into byte code. It's still plain text.
Free software has never been about the technical possibility of something, but a moral and cultural value. I.E. Just because you can, doesn't mean you should. So favor sites which don't obfuscate or make their (WASM) source code available as free software.
Shouldn't it be possible to decompile from wasm to the language that was used to compile to it (or any target language that could've produced said wasm)?
Yeah, but is that actually required? I don't know much about this, but I'd guess 90% of websites will strip this just like debug info in most proprietary software, 9% don't know about this or forget to remove it, if it's included by default and 1% consciously decides to ship it for transparency.
https://news.ycombinator.com/item?id=15958827