larger-image.html - mozsearch

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

<!DOCTYPE HTML>

<meta charset=utf-8>

<title>Largest Contentful Paint: largest image is reported.</title>

<body>

  <script src="/resources/testharness.js"></script>

  <script src="/resources/testharnessreport.js"></script>

  <script src="resources/largest-contentful-paint-helpers.js"></script>

  <!-- There is some text and some images. We care about lcp-133x106.png being reported, as it is the largest. -->

  <p>This is some text! :)</p>

  <img src='' id='lcp1' />

  <img src='' id='lcp2' />

  <img src='' id='lcp3' />

  <p>More text!</p>

  <script>

    // Add listener for load event that is fired when image is loaded.

    function image_load_promise(image_element) {

      return new Promise(resolve => {

        image_element.addEventListener('load', resolve);

});

    promise_test(async (t) => {

      assert_implements(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");

      let promise = image_load_promise(document.getElementById('lcp1'));

      document.getElementById('lcp1').src = '/images/lcp-100x50.png';

      await promise;

      const beforeLoad = performance.now();

      promise = image_load_promise(document.getElementById('lcp2'));

      document.getElementById('lcp2').src = '/images/lcp-133x106.png';

      await promise;

      promise = image_load_promise(document.getElementById('lcp3'));

      document.getElementById('lcp3').src = '/images/lcp-100x50-alt.png';

      await promise;

      const observer = new PerformanceObserver(

        t.step_func(entryList => {

          entryList.getEntries().forEach(entry => {

            // The text or other image could be reported as LCP if it is rendered before the larger image.

            if (entry.id !== 'lcp2')

              return;

            const url = window.location.origin + '/images/lcp-133x106.png';

            const size = 133 * 106;

            checkImage(entry, url, 'lcp2', size, beforeLoad);

            t.done();

})

})

);

      observer.observe({ type: 'largest-contentful-paint', buffered: true });

    }, 'Largest Contentful Paint: largest image is reported.');

  </script>

</body>