css/css-transitions/before-load-001.html

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>CSS Transitions Test: Transitioning before load event</title>
<meta name="assert" content="Test checks that transitions are run even before the load event fires">
<!-- NOTE: This test covers unspecified behavior and should probably be
     removed. It this behavior *were* specified, it would probably be
     specified here: -->
<link rel="help" title="5. Transition Events" href="https://drafts.csswg.org/css-transitions/#starting">
<link rel="author" title="Rodney Rehm" href="http://rodneyrehm.de/en/">

<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>

</head>
<body>

<script>
// Make sure a transition can run before the load event fires.

let loadEventFired = false;
window.addEventListener('load', () => {
  loadEventFired = true;
}, false);

async_test(t => {
  const div = addDiv(t, { style: 'transition: height .01s linear; ' +
                                 'height: 1px' });
  getComputedStyle(div).height;
  div.style.height = '100px';

  div.addEventListener('transitionrun', t.step_func_done(() => {
    assert_false(
      loadEventFired,
      'load event should not have fired yet'
    );
    document.getElementById('cat').src = '';
  }));
});
</script>

<img src="support/cat.png?pipe=trickle(d100)" id="cat">
</body>
</html>