layout-instability/recent-input.html

<!DOCTYPE HTML>
<meta charset=utf-8>
<title>Layout Instability: observe after user input</title>
<body>
<style>
#myDiv { position: relative; width: 300px; height: 100px; background: blue; }

/* Disable the button's focus ring, which otherwise expands its visual rect by
 * 1px on all sides, triggering a layout shift event.
 */
#button { outline: none; }
</style>
<div id='myDiv'></div>
<button id='button'>Generate a 'click' event</button>
<script src=/resources/testharness.js></script>
<script src=/resources/testharnessreport.js></script>
<script src=/resources/testdriver.js></script>
<script src=/resources/testdriver-vendor.js></script>
<script src=resources/util.js></script>
<script src=/event-timing/resources/event-timing-test-utils.js></script>
<script>
let timeAfterClick;

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();

  const observerPromise = new Promise(resolve => {
    const observer = new PerformanceObserver(
      entryList => {
        resolve(entryList);
      }
    ).observe({ entryTypes: ['layout-shift'] });
  });

  // User input event
  await clickAndBlockMain('button');

  // Modify the position of the div to trigger layout shift.
  document.getElementById('myDiv').style = "top: 60px";

  const layoutShiftEntryList = await observerPromise;
  const endTime = performance.now();

  assert_equals(layoutShiftEntryList.getEntries().length, 1);
  const entry = layoutShiftEntryList.getEntries()[0];
  assert_equals(entry.entryType, "layout-shift");
  assert_equals(entry.name, "");
  assert_greater_than(entry.startTime, startTime,
    "The layout shift entry startTime should be greater than the test startTime.");
  assert_less_than(entry.startTime, endTime,
    "The layout shift entry startTime should be less than the test endTime.");
  assert_equals(entry.duration, 0.0);
  // The layout shift value should be:
  // 300 * (100 + 60) * (60 / maxDimension) / viewport size.
  assert_equals(entry.value, computeExpectedScore(300 * (100 + 60), 60));
  // We should see that there was a click input entry.
  assert_equals(entry.hadRecentInput, true);
  assert_less_than(entry.lastInputTime, entry.startTime,
    "The lastInputTime should be less than the layout shift startTime.");

}, 'Layout shift right after user input is observable via PerformanceObserver.');
</script>

</body>