Superb article.

There was very little new information for me as I have applied some of these techniques myself based on having developed an intuitive understanding on how a rendering "thread" works and blocks, but for a less experienced developer this article should be incredibly enlightening and provide a solid understanding of what's happening.

I employed use of yielding on a hobby project [0] I made about 15 years ago, particularly when it had to do lots of draw operations on a canvas. I also experimented with using worker threads to render pieces of it on a background thread, but at the time there was no way to copy the data efficiently between them and the main thread, one had to send the data as a base64 encoded PNG and the overhead of encoding, decoding and then copying it onto the canvas made it perform far worse than just doing it all on the main thread.

The website also does Gzip decoding of uploaded files in JavaScript and the library I found at the time did all the work synchronously so could lock up the UI thread easily for 10+ seconds. I tweaked it to be able to yield every 200ms or something, the process of which was very educational, particularly due to it convincing me to never omit the curly braces after an if statement, I spent a very long time trying to understand why it wasn't working until eventually I realized a statement I added wasn't in the if statement's block. It's not that I didn't understand how if statements worked, it's that in my mind the lack of curly braces was initially invisible to me.

[0]: https://mordritch.com/mc_rss/

Reminds me of sprinkling DoEvents all over my VBA code to keep it "snappy" when I started to get into programming

Good article and I wish this was much better known.

The issue is though that it's too focused on interactivity. In reality, 90%++ of slow sites are not slow because of interactivity really, they are slow because they ship enormous react/nextjs bundles and have extremely heavy hydration work to do.

_so many_ sites have bundles >10MB that need to be downloaded, parsed and hydrated.

I've even seen (many) sites which have multiple SPAs stacked inside of them.

If you're on a slow internet connection and/or CPU the page is basically unusable for many tens of seconds and no amount of yielding post bundle hydrate will really solve that.

great article - explains in detail why my sans js websites run so smoothly and so fast.

I learned these lessons from many separate places and have always wished to see them in one place. This was an incredibly great article that I very much enjoyed reading and will be sending to anyone who's in need of ideas about speed. Thanks a lot!

Great piece, OP. We work in WASM and are considering web workers to help with rendering documents off the main thread in that context. I was surprised to read that ArrayBuffer is moved by reference only! Might be an option. Thanks for putting this together.

Top article, kudos! applied some of these techniques previously, and they do matter a lot. thing is, when you learn/teach JS there is usually limited time left to talk these topics, and they are essential more than it seems.

the whole point of cooperative multitasking is to yield now and then (back to the runner), so that it can process the drawing. Besides, at 60fps there's so much that can be computed once every N frames, and the eye does not see it, the animation flows.

It becomes even more interesting when webgpu is involved, but the CSS animator is indeed very fast.

note: some recent work of mine (newskool digital flyer sites) -> bsf.hmsu.org // nouveauxhivers.dub4powder.xyz

Excellent article, I went into it thinking the headline is obvious, but the examples are well crafted and it isn't just the obvious stuff.

This article concludes with the following statement:

> So much of development is trade-offs, and you have to choose according to the situation, which ultimately comes down to the developer’s experience and judgment.

It’s a great article, but I think it is a bit behind the ball in framing scheduling problems as a matter of “experience and judgment”. The problem of allocating work to a scarce resource is one of the oldest and most well-studied in all of computer science. It would make sense to go consult a textbook on the matter before trying to reinvent the wheel.

Brilliant, I had no idea about this stuff. Thanks for writing it up.

On the price ticket example, on my device (Samsung A15, mediocre phone from 2024) I get 11 fps with the slow example and 30 fps with the fast one. (15 if I scroll!)

Is that a case of the back pressure you mentioned?

All the other (fast) examples are 60 fps though :)

One obvious tool that this article doesn't mention is Chrome's performance monitor. Many techniques in the article only have to be applied once you can verify that they are running slow.

In the first example: doesn't pushing the button while typing cause the textfield lose focus? What's the point of the typing in the example?

Nice examples, a bit repetetive perhaps.

One thing that I found quite interesting to see is how the behaviour of the "4.000 particles" demo changes between the 5ms rendering and the "everything now" rendering.

Such an excellently written articles with really nice interactive visualizations!

I want to do a blanket response to people calling this AI slop: the post was written in korean and translated to english. Calling this slop is judgment slop.

I wish await in JavaScript could conditionally yield. Instead I end up having to use arounds like if (shouldYield()) await do yield();

Actor Model, dedicated or shared application worker. Full support for multi-window apps. Resolved since 2019. 26000 commits in, and counting. You are welcome!

https://github.com/neomjs/neo/blob/dev/learn/benefits/body/O...

DELETE ARTICLE BACK PRESSURE! .

FLIGHT §%=

The javascript web is. Restore the interop with noscript/basic HTML and it will lean towards sanity, something lost a few years ago.

localStorage is a webworker

SANDBOX MISSING

.setTimeout(0)

CANNOT C

> So what if off-screen posts were left as empty shells that only take up their height, and got filled with real content as they approach the screen?

Yeah fuck everyone doing that, hello Reddit, Outlook for Web or Bluesky. It makes searching on such "feed" pages with the browser's search function an utter pain in the ass, made worse by the fact that the platforms' own search functions are outright braindead.

Yeah, but if your website with, you know, text and stuff, doesn't do any stupid and unnecessary crap, it doesn't matter where the nonexistent unnecessary yet expensive code doesn't run.

Sandbox missing

.setTimeout(0)

So this is AI slop written? Why would anyone believe I'd want to read AI spam?

Also, the issue I see is who controls browsers as much more profound. We need to find a solution here, as the browser is too important to allow private companies to keep mankind hostage.

Edit: Wow, and the praise-accounts. Is that new on hackernews?

AI;DR – too bad as the content seems to be worthwhile, but then why not take the trouble to write it up yourself. Have it proofread/edited/spruced up all you want afterward, but don't have it do all (or most of) the writing.