File: image-loading-lazy-srcset.html

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<!DOCTYPE html>
<head>
<title>loading='lazy' image with srcset</title>
<link rel="help" href="https://html.spec.whatwg.org/multipage/images.html#update-the-image-data">
<link rel="help" href="https://html.spec.whatwg.org/multipage/images.html#will-lazy-load-image-steps">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
</head>
<div style="height:1000vh;"></div>
<img srcset="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABQAAAAUCAIAAAAC64paAAAAG0lEQVR42mP8z0A%2BYKJA76jmUc2jmkc1U0EzACKcASfOgGoMAAAAAElFTkSuQmCC" loading="lazy">
<img loading="lazy" srcset="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABQAAAAUCAIAAAAC64paAAAAG0lEQVR42mP8z0A%2BYKJA76jmUc2jmkc1U0EzACKcASfOgGoMAAAAAElFTkSuQmCC">
<script>
promise_test(async t => {
  let loaded_images = 0;
  const imgs = document.querySelectorAll("img");
  imgs.forEach(img => {
    img.addEventListener("load", () => { loaded_images++; }, { once: true });
  });

  await new Promise(resolve => window.addEventListener("load", resolve));

  assert_equals(loaded_images, 0,
                "lazy-load images with srcset shouldn't be loaded yet");

  const promises = [
    new Promise(resolve => imgs[0].addEventListener("load", resolve)),
    new Promise(resolve => imgs[1].addEventListener("load", resolve)),
  ];

  imgs[1].scrollIntoView();
  await Promise.all(promises);

  imgs.forEach(img => {
    assert_true(img.complete,
                "Now the lazy-load image with srcset should be loaded");
  });
});
</script>