Let's prototype a JavaScript JIT compiler!
Andreas KlingCited 4× on HN, 2023–2025
tutorial · advanced · evergreen · 2023–2025 on HN
Andreas Kling live-codes a prototype JavaScript JIT compiler for the LibJS engine used in SerenityOS and Ladybird. He builds a standalone bytecode VM, a simple interpreter, and then a simple JIT in about 80 minutes.
HN commenters cite it as a concrete example of how a skilled developer uses Copilot, mostly as fancy autocomplete for codebase-specific work.
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4 comments from Hacker News
Ladybird is 425k LOC. Chromium is 3.5m LOC. Starting a new browser, using LLMs... Is not going to maintain enough context. Whilst Andreas does use Copilot a fair bit [0], he tends to do a line at a time, frequently disagree and rewrites his own, before prompting again. That is... He basically uses it as a fancy autocomplete. Not much else. [0] ▶ this video
> The code is usually the same code I'd get a few web searches away My impression is that people normally don't use Copilot as a substitute for finding solutions (ChatGPT is much better for that), but as a way to help with otherwise tedious tasks that are really specific to your codebase. Check out 6:05 and 6:25 in this Andreas Kling video for a good example: ▶ this video Regarding your second point Copilot helps me when I least expects it. I think the video illustrates what I mean with that as well.
> Check out 6:05 and 6:25 in this Andreas Kling video for a good example: ▶ this video Oof. So not only was it a poor replacement for a macro, it didn't even generate the correct code!
The stuff Copilot helps me with is not the stuff SO could help me with. Check out 6:05 and 6:25 in this Andreas Kling video: ▶ this video That's where Copilot shines, not for locating and copypasting answers from Stack Overflow.