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Test Info: Warnings

<meta charset=utf-8>
<title>Layout Instability: observe after user input</title>
#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; }
<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>
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 =;
const observerPromise = new Promise(resolve => {
const observer = new PerformanceObserver(
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 =;
assert_equals(layoutShiftEntryList.getEntries().length, 1);
const entry = layoutShiftEntryList.getEntries()[0];
assert_equals(entry.entryType, "layout-shift");
assert_equals(, "");
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.');