File: lazy-out-of-band-load.html

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<!doctype html>
<title>Lazy loaded image doesn't get loaded eagerly after another image gets loaded with the same source</title>
<link rel="help" href="https://github.com/whatwg/html/issues/10671">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<body>
<script>
async function run_test(prop, image, t) {
  let value = `${image}?lazy-out-of-band-load-` + Math.random();
  let img = document.createElement("img")
  img[prop] = value;
  img.loading = "lazy";
  img.style.display = "none";
  img.addEventListener("error", t.unreached_func("error: should never try to load"));
  img.addEventListener("load", t.unreached_func("load: should never try to load"));
  document.body.appendChild(img);

  await new Promise(r => t.step_timeout(r, 100));

  // now load another image with the same src, but not lazy.
  img = document.createElement("img");
  img[prop] = value;

  await new Promise(r => {
    img.addEventListener("load", r, { once: true });
    img.addEventListener("error", r, { once: true });
    document.body.appendChild(img);
  });

  // Wait a bit to make sure we don't get a broken load.
  await new Promise(r => t.step_timeout(r, 100));
}

for (let prop of ["src", "srcset"]) {
  for (let path of ["/images/green.png", "/images/not-found"]) {
    promise_test(t => run_test(prop, path, t), `${prop} = ${path}`);
  }
}
</script>