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Test Info: Warnings

<title>Largest Contentful Paint: initially out-of-viewport image gets an LCP entry once they are visible.</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
.flex-container {
display: flex;
flex-direction: row;
width: 1000px;
overflow-x: hidden;
scroll-behavior: auto;
<div class='flex-container' id="container">
<img src='/images/yellow.png?pipe=trickle(d1)' width="1000" height="1000"/>
<img src='/images/green-1x1.png?1' width="1000" height="1000"/>
<img src='/images/green-1x1.png?2' width="1000" height="1000"/>
<img src='/images/green-1x1.png?3' width="1000" height="1000"/>
// Spin the carousel
setup({"hide_test_state": true});
const images = document.querySelectorAll('img');
let selected = 0;
const container = document.getElementById("container");
const transition = () => {
container.scrollLeft = selected * 1000;
selected = (selected + 1) % images.length;
setInterval(transition, 1000);
promise_test(async t => {
return new Promise(resolve => {
"LargestContentfulPaint is not implemented");
const observer = new PerformanceObserver(entryList => {
entryList.getEntries().forEach(entry => {
// May receive a text entry. Ignore that entry.
if (!entry.url) {
assert_true(entry.url.includes("yellow.png"), "Re-visible image has an entry");
observer.observe({type: 'largest-contentful-paint', buffered: true});
t.step_timeout(() => {
assert_unreached("The image should have become visible by now, which should have triggered an LCP entry.");
}, 2000);
}, 'Image visibility: out-of-viewport images are observable by LargestContentfulPaint once they become visible.');