For WASM you can probably use tools like ghidra to decompile and read.

Sure, as I said it's similar to decompiling normal binaries, which is hard to read (even when you're used to it).

Minified js not a lot better then raw ASM, single letter names and crazy optimisation patterns will make your life hell. Patching both I think is out of the question, maybe just inject some new js that interact with the DOM.

I'm not talking about reading minified JS. I'm saying: un-minifying JS gets you a way more readable result than decompiling native binaries does. I've done both more than often enough to know this difference well.

I've written mods and patches for dozens of minified sites, and it's never been too hard. I've written mods and patches for native applications, and it's waaaay harder - even just finding free space in the binary where you can inject your code and jump to/from is annoying, let alone actually writing your changes in ASM. All of this is immediately solved even with minified JS.