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Let's prototype a JavaScript JIT compiler!

Andreas Kling0 HN recommenders · 2023–2025
49K views · tutorial · evergreen · Uploaded 2023-10-11

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.

Compilers, interpreters & program analysisSoftware practice, open source & careers

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4 comments from Hacker News

@Kiro2023 · in “Stack Overflow announces 28% headcount reduction”

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: [VIDEO] That's where Copilot shines, not for locating and copypasting answers from Stack Overflow.

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@Kiro2023 · in “Krita AI Diffusion”

> 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: [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.

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@Nullabillity2023 · in “Krita AI Diffusion”

> Check out 6:05 and 6:25 in this Andreas Kling video for a good example: [VIDEO] Oof. So not only was it a poor replacement for a macro, it didn't even generate the correct code!

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@shakna2025 · in “This Month in Ladybird”

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] [VIDEO]

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