wpt/css/css-transitions/transition-zero-duration-with-delay.html at master · web-platform-tests/wpt · GitHub

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<!doctype html>
<html>
<head>
<meta charset=utf-8>
<title>CSS Transitions Test: 0-duration transition with delay applies after delay</title>
<meta name="assert" content="Transition with 0s duration and 0.3s delay applies property change after delay period">
<link rel="help" href="https://drafts.csswg.org/css-transitions/#starting">

<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="./support/helper.js"></script>

</head>
<body>
<div id="log"></div>

<script>
promise_test(async t => {
  const div = addDiv(t, {
    style: 'transition: width 0.1s; width: 0px;'
  });

  // Flush initial state
  getComputedStyle(div).width;
  // First transition to 100px
  div.style.width = '100px';
  await waitForTransitionEnd(div);

  // Change transition to 0s duration with 300ms delay
  div.style.transition = 'width 0s linear 0.3s';

  // Set width back to 0
  div.style.width = '0px';
  // Immediate check - should NOT have changed yet
  const computedStart = getComputedStyle(div).width;
  assert_equals(
    computedStart,
    '100px',
    'Width should remain at 100px initially'
  );
  // Wait for transitionend (should trigger after 300ms delay)
  await waitForTransitionEnd(div);

  // Verify final state
  const finalWidth = getComputedStyle(div).width;

  assert_equals(
    finalWidth,
    '0px',
    'Width should reset to 0 after delay'
  );

}, '0-duration transition with delay applies change after delay period');
</script>

</body>
</html>