display-none-prevents-starting-in-subtree.html

<!DOCTYPE html>
<link rel=author href="mailto:[email protected]">
<link rel=help href="https://drafts.csswg.org/css-animations/#animations">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/css/css-animations/support/testcommon.js"></script>
<style>
@keyframes margin {
    100% { margin-left: 200px }
}

#child {
  animation: margin 1s forwards;
}
</style>
<div id="container">
    <div>
        <div id="child"></div>
    </div>
</div>
<script>
test(() => {
  const container = document.getElementById("container");
  const animationCount = () => container.getAnimations({ subtree: true }).length;

  assert_equals(animationCount(), 1, `An animation is running on the child initially with "display: block" on the container.`);

  container.style.display = "none";
  assert_equals(animationCount(), 0, `Setting "display: none" on the container canceled the animation.`);

  container.style.marginLeft = "50px";
  container.firstElementChild.style.marginLeft = "100px";
  assert_equals(animationCount(), 0, `Manipulating styles on the container and a child element does not restart the animation.`);
}, 'Elements in a "display: none" tree cannot start CSS Animations.');
</script>

chromium/third_party/blink/web_tests/external/wpt/css/css-animations/display-none-prevents-starting-in-subtree.html