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<!DOCTYPE HTML>
<meta charset=utf-8>
<title>Largest Contentful Paint: src change triggers new entry.</title>
<body>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="resources/largest-contentful-paint-helpers.js"></script>
<img src='' id='image_id' />
<script>
setup({ "hide_test_state": true });
let first_image_src = '/images/black-rectangle.png';
let second_image_src = '/images/blue.png';
let image_id = 'image_id';
// Add listener for load event that is fired when image is loaded.
const image_load_promise = image_element => {
return new Promise(resolve => {
image_element.addEventListener('load', resolve);
});
}
// Create a promise that resolves when an LCP is observed.
const lcp_observation_promise = image_src => {
return new Promise(resolve => {
new PerformanceObserver((entryList) => {
let lcpEntry = entryList.getEntries().find(e => e.url.includes(image_src));
if (lcpEntry) {
resolve(lcpEntry);
}
}).observe({ type: 'largest-contentful-paint' });
});
}
const loadImageAndGetLCPEntry = async image_src => {
let LCPObserverPromise = lcp_observation_promise(image_src);
let image_element = document.getElementById(image_id);
let promise = image_load_promise(image_element);
image_element.src = image_src;
await promise;
return await LCPObserverPromise;
}
promise_test(async t => {
assert_implements(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
// Load first image.
let beforeLoad = performance.now();
let first_LCP = await loadImageAndGetLCPEntry(first_image_src);
// Verify first LCP entry correctness. The black-rectangle.png is 100 x 50.
checkImage(first_LCP, window.location.origin + first_image_src, image_id, 100 * 50, beforeLoad);
// Load second image.
beforeLoad = performance.now();
let second_LCP = await loadImageAndGetLCPEntry(second_image_src);
// Verify second LCP entry correctness. The blue.png is 133 by 106.
checkImage(second_LCP, window.location.origin + second_image_src, image_id, 133 * 106, beforeLoad);
}, 'Largest Contentful Paint: changing src causes a new entry to be dispatched.');
</script>
</body>
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