observe-text.html - mozsearch

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This WPT test may be referenced by the following Test IDs:
- /largest-contentful-paint/observe-text.html - WPT Dashboard Interop Dashboard

<!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>