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Test Info: Warnings
- This test has a WPT meta file that expects 1 subtest issues.
- This WPT test may be referenced by the following Test IDs:
- /largest-contentful-paint/first-paint-equals-lcp-text.html - WPT Dashboard Interop Dashboard
<!DOCTYPE HTML>
<meta charset=utf-8>
<title>LargestContentfulPaint compared with FirstPaint and FirstContentfulPaint on single text page.</title>
<body>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script>
setup({"hide_test_state": true});
async_test(function (t) {
assert_implements(window.PerformancePaintTiming, "PerformancePaintTiming is not implemented");
assert_implements(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
let firstPaintTime = 0;
let firstContentfulPaintTime = 0;
let largestContentfulPaintTime = 0;
const observer = new PerformanceObserver(
t.step_func(function(entryList) {
entryList.getEntries().forEach(entry => {
if (entry.name === 'first-paint') {
assert_equals(firstPaintTime, 0, 'Only one first-paint entry.');
assert_equals(entry.entryType, 'paint');
firstPaintTime = entry.startTime;
} else if (entry.name === 'first-contentful-paint') {
assert_equals(firstContentfulPaintTime, 0, 'Only one first-contentful-paint entry.');
assert_equals(entry.entryType, 'paint');
firstContentfulPaintTime = entry.startTime;
} else {
assert_equals(largestContentfulPaintTime, 0, 'Only one largest-contentful-paint entry.');
assert_equals(entry.entryType, 'largest-contentful-paint');
largestContentfulPaintTime = entry.renderTime;
}
// LCP fires necessarily after first-paint and first-contentful-paint.
if (largestContentfulPaintTime) {
assert_equals(firstContentfulPaintTime, largestContentfulPaintTime, 'FCP should equal LCP.');
// In PaintTiming spec, first-paint isn't a hard requirement, browsers can support
// first-contentful-paint only.
if (firstPaintTime) {
assert_less_than_equal(firstPaintTime, firstContentfulPaintTime, 'FP should be less than or equal to FCP.');
}
t.done();
}
});
})
);
observer.observe({type: 'largest-contentful-paint', buffered: true});
observer.observe({type: 'paint', buffered: true});
}, 'FCP and LCP are the same when there is a single text element in the page.');
</script>
<p>Text</p>
</body>