Links on Performance

• Making GitHub’s new homepage fast and performant — Tobias Ahlin describes how the scrolling effects are done more performantly thanks to IntersectionObserver and the fact that it avoids the use of methods that trigger reflows, like getBoundingClientRect. Also, WebP + SVG masks!
  
• Everything we know about Core Web Vitals and SEO — Simon Hearne covers why everyone is so obsessed with CWV right now: SEO. Simon says something I’ve heard a couple of times: The Page Experience Update is more of a carrot approach than stick — there is no direct penalty for failing to meet Google’s goals. That is, you aren’t penalized for poor CWV, but are given a bonus for good numbers. But if everyone around you is getting that bonus except you, isn’t that the same as a penalty?
  
• Setting up Cloudflare Workers for web performance optimisation and testing — Matt Hobbs starts with a 101 intro on setting up a Cloudflare Worker, using it to intercept a CSS file and replace all the font-family declarations with Comic Sans. Maybe that will open your eyes to the possibilities: if you can manipulate all assets like HTML, CSS, and JavaScript, you can force those things into doing more performant things.
  
• Now THAT’S What I Call Service Worker! — Jeremy Wagner sets up a “Streaming” Service Worker that caches common partials on a website (e.g. the header and footer) such that the people of Waushara County, Wisconsin, who have slow internet can load the site somewhere in the vicinity of twice as fast. This is building upon Philip Walton’s “Smaller HTML Payloads with Service Workers” article.
  
• Who has the fastest F1 website in 2021? — Jake Archibald’s epic going-on-10-part series analyzing the performance of F1 racing websites (oh, the irony). Looks like Red Bull is in the lead so far with Ferarri trailing. There is a lot to learn in all these, and it’s somewhat cathartic seeing funny bits like, Their site was slow because of a 1.8MB blocking script, but 1.7MB of that was an inlined 2300×2300 PNG of a horse that was only ever displayed at 20×20. Also, I don’t think I knew that Jake was the original builder of Sprite Cow! (Don’t use that because it turns out that sprites are bad.)
  
• Real-world CSS vs. CSS-in-JS performance comparison — Tomas Pustelnik looks at the performance implications of CSS-in-JS. Or, as I like to point out: CSS-in-React, as that’s always what it is since all the other big JavaScript frameworks have their own blessed styling solutions. Tomas didn’t compare styled-components to hand-written vanilla CSS, but to Linaria, which I would think most people still think of as CSS-in-JS — except that instead of bundling the styles in JavaScript, it outputs CSS. I agree that, whatever a styling library does for DX, producing CSS seems like the way to go for production. Yet another reason I like css-modules. Newer-fancier libs are doing it too.
  
• The Case of the 50ms request — Julia Evans put together this interactive puzzle for trying to figure out why a server request is taking longer than it should. More of a back-end thing than front-end, but the troubleshooting steps feel familiar. Try it on your machine, try it on my machine, see what the server is doing, etc.

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