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Test Info: Warnings

<meta charset=utf-8>
<title>Largest Contentful Paint: largest image is reported.</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="resources/largest-contentful-paint-helpers.js"></script>
<!-- There is some text and some images. We care about blue.png being reported, as it is the largest. -->
<p>This is some text! :)</p>
<img src='' id='red' />
<img src='' id='blue' />
<img src='' id='black' />
<p>More text!</p>
// Add listener for load event that is fired when image is loaded.
function image_load_promise(image_element) {
return new Promise(resolve => {
image_element.addEventListener('load', resolve);
promise_test(async (t) => {
assert_implements(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
let promise = image_load_promise(document.getElementById('red'));
document.getElementById('red').src = '/images/red.png';
await promise;
const beforeLoad =;
promise = image_load_promise(document.getElementById('blue'));
document.getElementById('blue').src = '/images/blue.png';
await promise;
promise = image_load_promise(document.getElementById('black'));
document.getElementById('black').src = '/images/black-rectangle.png';
await promise;
const observer = new PerformanceObserver(
t.step_func(entryList => {
entryList.getEntries().forEach(entry => {
// The text or other image could be reported as LCP if it is rendered before the blue image.
if ( !== 'blue')
const url = window.location.origin + '/images/blue.png';
// blue.png is 133 by 106.
const size = 133 * 106;
checkImage(entry, url, 'blue', size, beforeLoad);
observer.observe({ type: 'largest-contentful-paint', buffered: true });
}, 'Largest Contentful Paint: largest image is reported.');