iframe-loading-lazy-multiple-times.html

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This WPT test may be referenced by the following Test IDs:
- /html/semantics/embedded-content/the-iframe-element/iframe-loading-lazy-multiple-times.html - WPT Dashboard Interop Dashboard

<!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>