Tag: Performance

A Bit of Performance

Here’s a great post by Roman Komarov on what he learned by improving the performance of his personal website. There’s a couple of neat things he does to tackle font loading in particular, such as adding the <link rel="preload"> tags for fonts. This will encourage those font files to download a tiny bit faster which prevents that odd flash of un-styled text we know all too well. Roman also subsets his font files based on language which I find super interesting – as only certain pages of his website use Cyrillic glyphs.

He writes:

I was digging into some of the performance issues during my work for a few weeks, and I thought that it can be interesting to see how those could be applied to my site. I was already quite happy with how it performed (being just a small static site) but managed to find a few areas to improve.

I had also never heard of Squoosh, which happens to be an incredible image optimization tool that looks like this when you’re editing an image:

With that slider in the middle, it shows the difference between the original image and the newly optimized one, which is both super neat and helpful.

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CSS and Network Performance

JavaScript and images tend to get the bulk of the blame for slow websites, but Harry explains very clearly why CSS is equally to blame and harder to deal with:

  1. A browser can’t render a page until it has built the Render Tree;
  2. the Render Tree is the combined result of the DOM and the CSSOM;
  3. the DOM is HTML plus any blocking JavaScript that needs to act upon it;
  4. the CSSOM is all CSS rules applied against the DOM;
  5. it’s easy to make JavaScript non-blocking with async and defer
  6. making CSS asynchronous is much more difficult;
  7. so a good rule of thumb to remember is that your page will only render as quickly as your slowest stylesheet.

There are lots of options to do better with this, including some interesting things that HTTP/2 unlocks.

Check out Šime Vidas’s takeaways as well. It’s all fascinating, but the progressive rendering stuff is particularly cool. I suspect many CSS-in-JS libraries could/should help with doing things this way.

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