<!DOCTYPE HTML>
<meta charset=utf-8>
<title>Largest Contentful Paint: Progressively Loaded Image</title>
<body>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="resources/largest-contentful-paint-helpers.js"></script>
<script src="/common/get-host-info.sub.js"></script>
<script>
promise_test(async function (t) {
assert_implements(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
const beforeLoad = performance.now();
const observer = new PerformanceObserver(
t.step_func_done(function(entryList) {
assert_equals(entryList.getEntries().length, 1);
const entry = entryList.getEntries()[0];
const imgElement = document.getElementById('image_id');
const imageSrc = imgElement.currentSrc;
const imageWidth = imgElement.naturalWidth;
const imageHeight = imgElement.naturalHeight;
const size = imageWidth * imageHeight;
const lcpLoadTime = entry.loadTime;
const lcpRenderTime = entry.renderTime;
const resLoadTime = calculateResourceLoadTime(imageSrc);
assert_greater_than_equal(lcpLoadTime,resLoadTime,'Load before LCP event fired');
assert_greater_than_equal(lcpRenderTime,resLoadTime,'Load before LCP event rendered');
checkImage(entry, imageSrc, 'image_id', size, beforeLoad);
})
);
observer.observe({type: 'largest-contentful-paint', buffered: true})
}, 'Ensure Progressive JPEG LCP load and render events occur after resource loading');
function calculateResourceLoadTime(imageSrc) {
const entries = performance.getEntriesByName(imageSrc);
const resourceEntry = entries[0];
assert_equals(entries.length, 1, 'No Resource timing entry found');
return resourceEntry.responseEnd;
}
</script>
<img src='/images/computer.jpg?pipe=trickle(982:d1)' id='image_id'/>
</body>
</html>
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