element-timing/css-generated-text.html

<!DOCTYPE HTML>
<meta charset=utf-8>
<title>Element Timing: observe generated CSS text</title>
<style>
p::before {
  content: "Generated text prefix";
}
body {
  margin: 20px;
}
</style>
<body>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="resources/element-timing-helpers.js"></script>
<p elementtiming='my_text' id='text_id'></p>
<script>
  async_test(function (t) {
    const beforeRender = performance.now();
    assert_implements(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
    const observer = new PerformanceObserver(
      t.step_func_done(function(entryList) {
        assert_equals(entryList.getEntries().length, 1);
        const entry = entryList.getEntries()[0];
        checkTextElement(entry, 'my_text', 'text_id', beforeRender, document.getElementById('text_id'));
        assert_equals(entry.intersectionRect.left, 20, 'left should be 20.');
        assert_equals(entry.intersectionRect.top, 20, 'top should be 20.');
        // Try a lower bound of height=10, width=80 for the generated text.
        assert_greater_than_equal(entry.intersectionRect.right, 100);
        assert_greater_than_equal(entry.intersectionRect.bottom, 30);
      })
    );
    observer.observe({type: 'element', buffered: true});
  }, 'Generated text content is observable.');
</script>
</body>