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<!DOCTYPE html>
<head>
<title>Iframes with loading='lazy' load when in the viewport</title>
<link rel="author" title="Scott Little" href="mailto:sclittle@chromium.org">
<link rel="help" href="https://github.com/scott-little/lazyload">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
</head>
<script>
const t = async_test("Test that iframes with loading='lazy' load once they " +
"enter the viewport.");
let has_window_loaded = false;
let has_in_viewport_loaded = false;
const in_viewport_iframe_onload = t.step_func(() => {
assert_false(has_in_viewport_loaded,
"The in_viewport element should load only once.");
has_in_viewport_loaded = true;
});
window.addEventListener("load", t.step_func(() => {
assert_true(has_in_viewport_loaded,
"The in_viewport element should have loaded before " +
"window.load().");
assert_false(has_window_loaded,
"The window.load() event should only fire once.");
has_window_loaded = true;
document.getElementById("below_viewport").scrollIntoView();
}));
const below_viewport_iframe_onload = t.step_func_done(() => {
assert_true(has_window_loaded,
"The window.load() event should have fired before " +
"below_viewport loaded.");
});
</script>
<body>
<iframe id="in_viewport" src="resources/subframe.html?in-viewport"
loading="lazy" width="200px" height="100px"
onload="in_viewport_iframe_onload();"></iframe>
<div style="height:1000vh;"></div>
<iframe id="below_viewport" src="resources/subframe.html?below-viewport"
loading="lazy" width="200px" height="100px"
onload="below_viewport_iframe_onload();"></iframe>
<!-- This async script loads very slowly in order to ensure that, if the
below_viewport element has started loading, it has a chance to finish
loading before window.load() happens, so that the test will dependably
fail in that case instead of potentially passing depending on how long
different resource fetches take. -->
<script async src="/common/slow.py"></script>
</body>
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