observe-text.html | Explore in Territory

<!DOCTYPE HTML>
<meta charset=utf-8>
<title>Largest Contentful Paint: observe text.</title>
<body>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
p {
  font-size: 12px;
}
</style>
<script>
  async_test(function (t) {
    assert_implements(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
    let beforeRender;
    const observer = new PerformanceObserver(
      t.step_func_done(function(entryList) {
        assert_equals(entryList.getEntries().length, 1);
        const entry = entryList.getEntries()[0];
        assert_equals(entry.entryType, 'largest-contentful-paint');
        assert_greater_than_equal(entry.renderTime, beforeRender);
        assert_greater_than_equal(performance.now(), entry.renderTime);
        assert_approx_equals(entry.startTime, entry.renderTime, 0.001,
          'startTime should be equal to renderTime to the precision of 1 millisecond.');
        assert_equals(entry.duration, 0);
        // Some lower bound: height of at least 12 px.
        // Width of at least 100 px.
        // TODO: find a good way to bound text width.
        assert_greater_than_equal(entry.size, 1200);
        assert_equals(entry.loadTime, 0);
        assert_equals(entry.id, 'my_text');
        assert_equals(entry.url, '');
        assert_equals(entry.element, document.getElementById('my_text'));
      })
    );
    observer.observe({type: 'largest-contentful-paint', buffered: true});
    beforeRender = performance.now();
  }, 'Text element is observable as a LargestContentfulPaint candidate.');
</script>

<p id='my_text'>This is important text! :)</p>
</body>
chromium/third_party/blink/web_tests/external/wpt/largest-contentful-paint/observe-text.html
