layout-instability/toJSON.html

<!DOCTYPE HTML>
<meta charset=utf-8>
<title>Layout Instability: toJSON</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);

  return new Promise(resolve => {
    const observer = new PerformanceObserver(
      t.step_func(entryList => {
        const entry = entryList.getEntries()[0];
        assert_equals(typeof(entry.toJSON), 'function');
        const json = entry.toJSON();
        assert_equals(typeof(json), 'object');
        const keys = [
          // PerformanceEntry
          'name',
          'entryType',
          'startTime',
          'duration',
          // LayoutShift
          'value',
          'hadRecentInput',
          'lastInputTime',
        ];
        for (const key of keys) {
          assert_equals(json[key], entry[key],
            `LayoutShift ${key} entry does not match its toJSON value`);
        }
        resolve();
      })
    );
    observer.observe({type: 'layout-shift'});
    document.getElementById('myDiv').style = "top: 60px";
  });
}, 'Test toJSON() in LayoutShift.');
</script>
</body>