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<!DOCTYPE HTML>
<meta charset=utf-8>
<title>Largest Contentful Paint: largest image is reported.</title>
<body>
<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 lcp-133x106.png being reported, as it is the largest. -->
<p>This is some text! :)</p>
<img src='' id='lcp1' />
<img src='' id='lcp2' />
<img src='' id='lcp3' />
<p>More text!</p>
<script>
// 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('lcp1'));
document.getElementById('lcp1').src = '/images/lcp-100x50.png';
await promise;
const beforeLoad = performance.now();
promise = image_load_promise(document.getElementById('lcp2'));
document.getElementById('lcp2').src = '/images/lcp-133x106.png';
await promise;
promise = image_load_promise(document.getElementById('lcp3'));
document.getElementById('lcp3').src = '/images/lcp-100x50-alt.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 larger image.
if (entry.id !== 'lcp2')
return;
const url = window.location.origin + '/images/lcp-133x106.png';
const size = 133 * 106;
checkImage(entry, url, 'lcp2', size, beforeLoad);
t.done();
})
})
);
observer.observe({ type: 'largest-contentful-paint', buffered: true });
}, 'Largest Contentful Paint: largest image is reported.');
</script>
</body>
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