element-timing/images-repeated-resource.html

<!DOCTYPE HTML>
<meta charset=utf-8>
<title>Element Timing: observe elements with the same resource</title>
<body>
<style>
body {
  margin: 0;
}
</style>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="resources/element-timing-helpers.js"></script>
<script>
  let beforeRender;
  let numEntries = 0;
  let responseEnd1;
  let responseEnd2;
  let img;
  let img2;
  const index = window.location.href.lastIndexOf('/');
  const pathname = window.location.href.substring(0, index) +
      '/resources/square100.png';
  async_test(function (t) {
    if (!window.PerformanceElementTiming) {
      assert_unreached("PerformanceElementTiming is not implemented");
    }
    const observer = new PerformanceObserver(
      t.step_func(function(entryList) {
        entryList.getEntries().forEach(entry => {
          // Easier to check the |element| attribute here since element ID is the same for both images.
          checkElement(entry, pathname, entry.identifier, 'image_id', beforeRender, null);
          checkNaturalSize(entry, 100, 100);
          if (entry.identifier === 'my_image') {
            ++numEntries;
            responseEnd1 = entry.responseEnd;
            assert_equals(entry.element, img);
          }
          else if (entry.identifier === 'my_image2') {
            ++numEntries;
            responseEnd2 = entry.responseEnd;
            assert_equals(entry.element, img2);
          }
        });
        if (numEntries == 2) {
          assert_equals(responseEnd1, responseEnd2);
          t.done();
        }
      })
    );
    observer.observe({entryTypes: ['element']});
    // We add the images during onload to be sure that the observer is registered
    // in time for it to observe the element timing.
    window.onload = () => {
      // Add image of width and height equal to 100.
      img = document.createElement('img');
      img.src = 'resources/square100.png';
      img.setAttribute('elementtiming', 'my_image');
      img.setAttribute('id', 'image_id');
      document.body.appendChild(img);

      img2 = document.createElement('img');
      img2.src = 'resources/square100.png';
      img2.setAttribute('elementtiming', 'my_image2');
      img2.setAttribute('id', 'image_id');
      document.body.appendChild(img2);

      beforeRender = performance.now();
    };
  }, 'Element with elementtiming attribute is observable.');
</script>

</body>