Creating a page full of product shots, animations, and videos that still loads fast and performs well can be tricky. Throughout the process of building GitHub’s new homepage, we’ve used the Core Web Vitals as one of our North Stars and measuring sticks. We’re going to take a deep-dive here into two of the strategies that produced the overall biggest performance impact for us: crafting high performance animations and serving the perfect image.
So in summary, when you are preloading fonts make sure that what is preloaded matches with the src defined in your @font-face rules. Remember the first src the browser finds wins. If these don’t match then your users may be downloading two sets of exactly the same fonts. Make sure you check your browser console for preload warnings and font 404 errors. As both of these issues can seriously impact page performance and adding to the data requirements for the site.
Summary: Maintaining a consistent width-to-height ratio, called an aspect ratio, is critical in responsive web design and for preventing cumulative layout shift. Now, there’s a more straightforward way to do this with the new aspect-ratio property launching in Chromium 88, Firefox 87, and Safari Technology Preview 118.
I couldn’t think of how this sort of thing would be useful, but then I saw the Porky Pig cartoon animation. He emerges from behind the bottom frame, but his face overlaps and stacks on top of the top edge of the same frame — the exact same sort of clipping situation we saw earlier. That’s when my wheels started turning. Could I replicate that effect using just CSS? And for extra credit, could I replicate it using a single <div>?