element-timing/image-not-added.html

<!DOCTYPE HTML>
<meta charset=utf-8>
<title>Element Timing: do not observe a disconnected image</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script>
  async_test(function (t) {
    assert_implements(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
    const observer = new PerformanceObserver(
      t.step_func_done(() => {
        // The image should not have caused an entry, so fail test.
        assert_unreached('Should not have received an entry!');
      })
    );
    observer.observe({entryTypes: ['element']});
    // We add the image 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 equal to 100 and height equal to 100.
      const img = document.createElement('img');
      img.src = 'resources/square100.png';
      img.setAttribute('elementtiming', 'my_image');
      img.setAttribute('id', 'my_id');
      // Image has been created but not added.
      // Wait for 500ms and end test, ensuring no entry was created.
      t.step_timeout(() => {
        t.done();
      }, 500);
    };
  }, 'Image which is not added to DOM tree is not observable.');
</script>