<head>
<title>Images with loading='lazy' can be lazy loaded multiple times</title>
<link rel="author" title="Dom Farolino" href="mailto:[email protected]">
<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 image out-of-view later in the test -->
<div id="top_div"></div>
<div style="height:1000vh;"></div>
<img id="below_viewport" loading="lazy" src="resources/image.png?image-loading-lazy-multiple-times-first">
<script>
const t = async_test("Images with loading='lazy' can be lazy loaded multiple times");
const image = document.querySelector('#below_viewport');
const top_div = document.querySelector('#top_div');
let has_window_load_fired = false;
// This should be triggered first.
window.addEventListener('load', t.step_func(() => {
has_window_load_fired = true;
// Scroll the loading=lazy below-viewport image into view, so that it loads.
image.scrollIntoView();
}));
image.onload = t.step_func(() => {
assert_true(has_window_load_fired,
"The loading=lazy below-viewport image should not block the " +
"window load event");
changeImageSourceAndScrollToTop();
});
function changeImageSourceAndScrollToTop() {
top_div.scrollIntoView();
// Allow some time for scroll back to top, since we don't
// want the image to still be in the viewport and trigger a
// load due to the scroll being slow.
t.step_timeout(() => {
// Lazily load a "different" image.
image.src = 'resources/image.png?image-loading-lazy-multiple-times-second';
image.onload =
t.unreached_func("The loading=lazy below-viewport image should lazily " +
"load its second image, and not load it eagerly when " +
"the `src` attribute is changed");
// In 1s, scroll the image *back* into view, and record that it loads
// successfully.
t.step_timeout(() => {
image.onload = t.step_func_done();
image.scrollIntoView();
}, 1000);
}, 500);
}
</script>
</body>
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