image-loading-lazy-below-viewport.html

<!DOCTYPE html>
<div style="height:1000vh;"></div>

<img id="img" loading="lazy" src="image.png?lazy-below-viewport">

<script>
  const img = document.querySelector('#img');

  img.addEventListener("load", () => {
    parent.postMessage("image_loaded", "*");
  });

  window.addEventListener("load", () => {
    parent.postMessage("window_loaded", "*");
  });

  window.addEventListener("message", event => {
    if (event.data == "scroll") {
      img.scrollIntoView();
    }
  });
</script>

chromium/third_party/blink/web_tests/external/wpt/html/semantics/embedded-content/the-img-element/resources/image-loading-lazy-below-viewport.html