<!DOCTYPE html>
<head>
  <title>Iframes with loading='lazy' can be lazy loaded multiple times</title>
  <link rel="author" title="Dom Farolino" href="mailto:dom@chromium.org">
  <link rel="help" href="https://html.spec.whatwg.org/multipage/urls-and-fetching.html#lazy-loading-attributes">
  <script src="/resources/testharness.js"></script>
  <script src="/resources/testharnessreport.js"></script>
</head>

<body>
  <!-- This is used to represent the top of the viewport, so we can scroll the
       below-viewport iframe out-of-view later in the test -->
  <div id="top_div"></div>
  <div style="height:1000vh;"></div>
  <iframe id="below_viewport" loading="lazy" src="resources/unload-reporter.html?first"></iframe>

<script>
  const t = async_test();
  const iframe = document.querySelector('#below_viewport');
  const top_div = document.querySelector('#top_div');

  let has_window_load_fired = false;
  let iframe_being_unloaded = false;

  // This should be triggered first.
  window.addEventListener('load', t.step_func(() => {
    has_window_load_fired = true;
    // Scroll the loading=lazy below-viewport iframe into view, so that it loads.
    iframe.scrollIntoView();
  }));

  window.addEventListener('message', t.step_func(msg => {
    if (msg.data === 'unloading')
      iframe_being_unloaded = true;
  }));

  iframe.onload = t.step_func(() => {
    assert_true(has_window_load_fired,
                "The loading=lazy below-viewport iframe should not block the " +
                "window load event");
    changeIframeSourceAndScrollToTop();
  });

  function changeIframeSourceAndScrollToTop() {
    top_div.scrollIntoView();

    // Lazily load a "different" iframe.
    iframe.src = 'resources/unload-reporter.html?second';
    iframe.onload =
      t.unreached_func("The loading=lazy below-viewport iframe should lazily " +
                       "load its second resource, and not load it eagerly " +
                       "when the `src` attribute is changed");

    // In 1s, scroll the iframe *back* into view, and record that it loads
    // successfully.
    t.step_timeout(() => {
      assert_false(iframe_being_unloaded,
                   "The iframe's old resource is not eagerly unloaded");

      iframe.onload = t.step_func_done(() => {
        assert_true(iframe_being_unloaded,
                    "The iframe's old resources was unloaded correctly");
      });

      iframe.scrollIntoView();
    }, 1000);
  }
</script>
</body>
