just why

Welp, turns out it’s not real. Just opening DevTools makes all timers 5-100× slower, due to the overhead of capturing stack traces. Even if you do nothing else (don’t record performance, etc)! Guess who accidentally spent a weekend optimizing this 😅 (h/t @paul.irish for explaining why)

Okay, so this is pretty wild: apparently, in Chromium, the deeper you are in the call stack, the slower your `setTimeout()` calls become? gist.github.com/iamakulov/85...

Why are native setTimeout and clearTimeout calls so expensive? Like, here it takes 1.5 ms. What’s the technical reason it’s so slow? Just 100-200 of those in a row (trivial if you’re mounting a bunch of React components that set timers) will easily block the page.

Belated hi from @perfnow.nl! Come talk to us (me & @kurtextrem.de) about React performance, Framer sites, LCP/INP and more :D

Neat lil learning from today’s @perfnow.nl (via Umar Hansa): You can now throttle individual requests in Chrome! Neat for experimenting with stuff like - lazy-loading: does the UI look okay if this chunk takes MUCH longer to arrive - resilience: what happens if this specific CDN is extremely slow

This lil boy (www.framer.com/updates/cms...) actually took multiple weeks of full-time work! That’s because we didn’t only fix copy-paste papercuts, we also took an opportunity to improve Framer’s text editing architecture. Story time!

til oxlint does some insane tricks (custom js ast interface that understands rust memory layout!) to make js plugins fast github.com/oxc-project...

something very cool to see: Chrome recently shipped automatic <link rel="prefetch"> for all links in viewport you could do it previously with libs like Quicklink, but it’s super cool to see this implemented natively (it’s off by default, enabled with one html tag)

feels so good to be writing something again huh

Got bitten by `new URL()` today. Guess why this doesn’t work?

soon in @Framer.com: much better ⌘C ⌘V with google docs, notion, craft, and every other editor out there (my lil non-performance side project)

⚡ Lighthouse (incorrectly) punishes preloading If you’re like me, you probably struggled with Lighthouse scores at least once. “I already optimized everything; why is my score still yellow?” Often, the cause is there’s more to optimize. But sometimes, it’s Lighthouse itself.

Super cool React performance deep dive with @iamakulov.com 👏 @jsheroes.io #JSHeroes2025

📝 Wrote about that one time I was doing performance work and ran into an eval()-based JS minifier from 2004. (Also, it’s compatible with ES2024, guess what) 3perf.com/blog/packer/

Introducing @Framer.com Code Boundaries. No more optimization errors, no more blank pages, and no more searching for broken Components. (Or: how we went down the rabbit hole of React error handling for a month 🧵)

Stumbled upon a fun Chrome issue where you can get a high CLS score when nothing jumps on the screen – simply by using `content-visibility: auto`! Filed a bug: issues.chromium.org/issues/3911...

So excited to have @iamakulov.com this year on the conference. Stay tuned for the full lineup announcement!

This is the most comprehensive deep overview of React INP optimizations I’ve seen to date:

One of the best productivity tips I have ever learned at Framer (from @eelco.lempsink.nl) is: Whenever you want to ask a teammate for help, don’t DM them. Instead, always post your question in a channel (and cc them).

I found the dumbest way to preload an iframe ahead of time: <iframe src="..." sandbox="allow-same-origin"> • Downloads the iframe + its CSS/JS/etc • Puts these resources into the cache, so they’re there when you need them later • Critically, doesn’t execute any JS at all

Today in React wishlist: support for setting several refs on a single <div> github.com/facebook/rea...

This fix for this is so slick: instead of reverting back to the old behavior where Suspense fallbacks have to wait for suspended siblings to render, the new feature commits fallbacks immediately, then schedules a render for the siblings after to "pre-warm" the lazy requests in the tree.

you know what actually fuck you and in fact fuck the horse you rode in on "one of us only tells the truth and one only lies"-ass CSS property

Hi #perfnow! Glad to be at the main conf of the year for the next three days :)