element-timing/buffered-flag.html

<!DOCTYPE HTML>
<meta charset=utf-8>
<title>Element Timing: observe element with buffered flag</title>
<body>
<style>
body {
  margin: 0;
}
</style>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="resources/element-timing-helpers.js"></script>
<script>
  async_test(t => {
    assert_implements(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
    const beforeRender = performance.now();
    const img = document.createElement('img');
    // Initial observer used to know when entry has been dispatched
    new PerformanceObserver(() => {
      // Second observer should require buffered flag to receive the already-dispatched entry.
      new PerformanceObserver(t.step_func_done(entryList => {
        assert_equals(entryList.getEntries().length, 1);
        const entry = entryList.getEntries()[0];
        const pathname = window.location.origin + '/images/black-rectangle.png';
        checkElement(entry, pathname, 'my_image', 'my_id', beforeRender, document.getElementById('my_id'));
        // Test that viewport size is at least 100, so element is fully visible.
        assert_greater_than_equal(document.documentElement.clientWidth, 100, 'Width should be >= 100');
        assert_greater_than_equal(document.documentElement.clientHeight, 100, 'Height should be >= 100');

        checkRect(entry, [0, 100, 0, 50]);
        checkNaturalSize(entry, 100, 50);
      })).observe({type: 'element', buffered: true});
    }).observe({type: 'element'});
    img.src = '/images/black-rectangle.png';
    img.setAttribute('elementtiming', 'my_image');
    img.setAttribute('id', 'my_id');
    document.body.appendChild(img);
  }, 'Element Timing entries are observable via buffered flag.');
</script>
</body>