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Pseudo-elements in the Web Animations API

To use the Web Animations API (e.g. el.animate()) you need a reference to a DOM element to target. So, how do you use it on pseudo-elements, which don’t really offer a direct reference? Dan Wilson covers a (newish?) part of the API itself:

const logo = document.getElementById('logo');

logo.animate({ opacity: [0, 1] }, {
  duration: 100,
  pseudoElement: '::after'
});

I noticed in Dan’s article that ::marker is supported. I was just playing with that recently while doing our List Style Recipes page. I figured I’d give it a spin by testing the WAAPI and @keyframes on both a ::marker and and ::after element:

At first, I confused myself because it seemed like the WAAPI wasn’t working on ::after, but Dan reminded me that when using a transform, the element can’t be display: inline. Instead, I made it inline-block and it worked fine. However, I did uncover that @keyframes don’t seem to work on ::marker elements in Firefox — hopefully they’ll fix that (and we get Chrome and Safari support for ::marker ASAP).

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