I think I see what you are saying, but your statements aren't completely right which might be why you are being downvoted. "asm.js represents LLVM bytecode" is not right, just because you can compile one thing to another does not mean it represents it.

You make a good point though; it's not like we are seeing helpful warnings when writing our frontend JS apps. But those warnings are still crucial when actually building & deploying stuff; with various tooling and browsers it's really nice to see a "successful asm.js compilation" message and you know it's working. If you upgrade a tool, you can be sure that it's still working, etc.

Also, it's not uncommon for people to write new languages or compilers and having that feedback that you are on the fast path is really nice.

I think your point has some merit though.

The other benefit to AOT is simply that, when the app starts running, it immediately starts running in the fast path.