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:
- /layout-instability/buffered-flag.html - WPT Dashboard Interop Dashboard

<!DOCTYPE HTML>

<meta charset=utf-8>

<title>Layout Instability: PerformanceObserver sees entries with buffered flag</title>

<body>

<style>

#myDiv { position: relative; width: 300px; height: 100px; background: blue; }

</style>

<div id='myDiv'></div>

<script src="/resources/testharness.js"></script>

<script src="/resources/testharnessreport.js"></script>

<script src="resources/util.js"></script>

<script>

promise_test(async t => {

  assert_implements(window.LayoutShift, 'Layout Instability is not supported.');

  // Wait for the initial render to complete.

  await waitForAnimationFrames(2);

  const startTime = performance.now();

  return new Promise(resolve => {

    // First observer creates second in callback to ensure the entry has been dispatched by the time

    // the second observer begins observing.

    new PerformanceObserver(() => {

      const endTime = performance.now();

      // Second observer requires 'buffered: true' to see entries.

      new PerformanceObserver(t.step_func(list => {

        assert_equals(list.getEntries().length, 1);

        const entry = list.getEntries()[0];

        assert_equals(entry.entryType, "layout-shift");

        assert_greater_than_equal(entry.startTime, startTime);

        assert_less_than_equal(entry.startTime, endTime);

        assert_equals(entry.duration, 0.0);

        assert_equals(entry.value, computeExpectedScore(300 * (100 + 60),  60));

        resolve();

      })).observe({'type': 'layout-shift', buffered: true});

    }).observe({type: 'layout-shift'});

    // Modify the position of the div to cause a layout-shift entry.

    document.getElementById('myDiv').style = "top: 60px";

});

}, 'PerformanceObserver with buffered flag sees previous layout-shift entry.');

</script>

</body>