subframe-occlusion-tracking.html | Explore in Territory

<!DOCTYPE html>
<div id='target'>Hello, world!</div>

<script>
let observer = null;
let trackVisibility = true;

addEventListener("message", event => {
  if (observer) {
    observer.disconnect();
    observer = null;
    requestAnimationFrame(() => {
      setTimeout(() => {
        event.source.postMessage({expected: false}, "*");
      });
    });
  } else {
    observer = new IntersectionObserver(
      entries => {}, {trackVisibility: trackVisibility, delay: 100});
    observer.observe(document.getElementById('target'));
    requestAnimationFrame(() => {
      setTimeout(() => {
        event.source.postMessage({expected: trackVisibility}, "*");
        trackVisibility = !trackVisibility;
      });
    });
  }
});
</script>

chromium/third_party/blink/web_tests/http/tests/intersection-observer/resources/subframe-occlusion-tracking.html