longtask-timing/longtask-sync-xhr.html

<!DOCTYPE HTML>
<meta charset=utf-8>
<title>LongTask Timing: synchronous XHR</title>
<body>

<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="resources/utils.js"></script>

<h1>Long Task: synchronous XHR</h1>
<div id="log"></div>
<script>
setup(() => assert_implements(window.PerformanceLongTaskTiming, 'Longtasks are not supported.'));

promise_test(async t => {
    const receivedLongTask = new Promise(resolve =>
    new PerformanceObserver(entries => resolve(entries.getEntries())).observe({entryTypes: ['longtask']}));
    await new Promise(resolve => window.addEventListener('load', () => {
        const xhr = new XMLHttpRequest();
        xhr.open('GET', '/resource-timing/resources/delay-css.py?delay=100', false /* synchronous xhr */);
        xhr.send();
        resolve();
    }));
    const entries = await receivedLongTask;
    assert_equals(entries.length, 1);
}, 'A long synchronous XHR is a longtask');
</script>
</body>