css/css-animations/animation-style-element-replaced-with-keyframes-rule-of-same-name.html

<!doctype html>
<meta charset=utf-8>
<title>Changes to @keyframes rules</title>
<link rel="help" href="https://drafts.csswg.org/css-animations-1/">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="support/testcommon.js"></script>
<div id="log"></div>
<script>
'use strict';

test(t => {
  const div = addDiv(t);

  const originalStyleElement = document.createElement("style");
  originalStyleElement.textContent = '@keyframes anim-custom { from, to { left: 100px } }';
  document.head.appendChild(originalStyleElement);

  t.add_cleanup(() => originalStyleElement.remove());

  div.style.animation = 'anim-custom 100s';

  const computedStyle = getComputedStyle(div);
  assert_equals(computedStyle.left, "100px", "The initial @keyframes rule is applied");

  // Remove the original style element and add a new one with an animation with the same name.
  const newStyleElement = document.createElement("style");
  newStyleElement.textContent = '@keyframes anim-custom { from, to { left: 200px } }';
  originalStyleElement.replaceWith(newStyleElement);

  t.add_cleanup(() => newStyleElement.remove());

  assert_equals(computedStyle.left, "200px", "The new @keyframes rule is applied");
}, 'Replacing a <style> element with a new <style> element while both containing the different @keyframes rule with the same name dynamically updates running animations.');

</script>