[EagnaIonat]

You are probably doing something others have done before frequently.

I find the LLMs struggle constantly with languages there is little documentation or out of date. RAG, LoRA and multiple agents help, but they have their own issues as well.

[nl]

The OP was working on a "a small JavaScript/HTML web application"

This is a particular sweetspot for LLMs at the moment. I'll regularly one-shot entire NextJS codebases with custom styling in both Codex and Claude.

But it turns out the OP is using Copilot. That just isn't competitive anymore.

[weavejester]

I'll see if I can run the experiment again with Codex, if not on the exact same project then a similar one. The advice I'm getting in the other comments is that Codex is more state of the art.

As a quick check I asked Codex to look over the existing source code, generated via Copilot using the GPT-5 agent. I asked it to consider ways of refactoring, and then to implement them. Obviously a fairer test would be to start from scratch, but that would require more effort on my part.

The refactor didn't break anything, which is actually pretty impressive, and there are some improvements. However if a human suggested this refactor I'd have a lot of notes. There's functions that are badly named or placed, a number of odd decisions, and it increases the code size by 40%. It certainly falls far short of what I'd consider a capable coder should be doing.