buffered-flag.html

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This test has a WPT meta file that expects 1 subtest issues.
This WPT test may be referenced by the following Test IDs:
- /element-timing/buffered-flag.html - WPT Dashboard Interop Dashboard

<!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>