wpt/css/css-transitions/custom-property-and-allow-discrete.html at master · web-platform-tests/wpt · GitHub

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<!doctype html>
<html>
<head>
<meta charset=utf-8>
<title>CSS Transitions Test: transition of a custom property with "transition-behavior: allows-discrete"</title>
<meta name="assert" content="Checks that transitioning a custom property with 'transition-behavior: allows-discrete' works as expected">
<link rel="help" href="https://drafts.csswg.org/css-transitions-2/#transition-behavior-property">
<script src="/resources/testharness.js" type="text/javascript"></script>
<script src="/resources/testharnessreport.js" type="text/javascript"></script>
<script src="./support/helper.js" type="text/javascript"></script>
<style>
  .target {
    transition: --foo 10s step-end;
    transition-behavior: allow-discrete;
    --foo: bar;
  }
</style>
</head>
<body>
<div id="log"></div>
<script>
promise_test(async t => {
  const div = addDiv(t, { class: 'target' });

  let transitionCount = 0;
  div.addEventListener("transitionstart", () => transitionCount++);

  // Assert initial value.
  assert_equals(
    getComputedStyle(div).getPropertyValue('--foo').trim(),
    'bar',
    'Computed style reflects initial value before transition'
  );
  div.style.setProperty('--foo', 'baz');

  const anim = assertTransitionKeyframes(div, '--foo', 'bar', 'baz');
  await waitForAnimationFrames(2);

  assert_equals(transitionCount, 1, 'A single "transitionstart" event was dispatched');
  // Assert value during transition.
  assert_equals(
    getComputedStyle(div).getPropertyValue('--foo').trim(),
    'bar',
    'Computed style stays at the old value while transition is running'
  );

  anim.finish();
  await anim.finished;
  // Assert final value.
  assert_equals(
    getComputedStyle(div).getPropertyValue('--foo').trim(),
    'baz',
    'Computed style reflects the new value after transition ends'
  );
}, 'It is possible to transition an unregistered custom property using "transition-behavior: allows-discrete"');

promise_test(async t => {
  const div = addDiv(t);
  div.style.setProperty('--foo', 'bar');

  // Trigger a transition on the custom property.
  getComputedStyle(div).getPropertyValue('--foo');
  div.style.transition = "--foo 10s allow-discrete";
  div.style.setProperty('--foo', 'baz');

  assertTransitionKeyframes(div, '--foo', 'bar', 'baz');
}, 'It is possible to transition an unregistered custom property using "transition-behavior: allows-discrete" when setting "transition-property" in the style change that yields the transition');

</script>
</body>
</html>