servo/tests/wpt/web-platform-tests/preload/preload-xhr.html

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

const dummyContent = '<?xml version="1.0" encoding="utf-8"?>\n<root>Text.me</root>\n';
promise_test(async (t) => {
  const url = `resources/dummy.xml?token=${token()}`;
  const link = document.createElement('link');
  link.rel = 'preload';
  link.as = 'fetch';
  link.href = url;
  link.crossOrigin = 'anonymous';

  document.head.appendChild(link);

  const xhr = new XMLHttpRequest();
  await new Promise((resolve, reject) => {
    xhr.onloadend = resolve;
    xhr.onloaderror = reject;
    xhr.open('GET', url);
    xhr.send();
  });
  verifyNumberOfResourceTimingEntries(url, 1);
  assert_equals(xhr.status, 200);
  assert_equals(xhr.responseText, dummyContent);

}, 'Make an XHR request immediately after creating link rel=preload.');

promise_test(async (t) => {
  const url = `resources/dummy.xml?token=${token()}`;
  const link = document.createElement('link');
  link.rel = 'preload';
  link.as = 'fetch';
  link.href = url;
  link.crossOrigin = 'anonymous';

  await new Promise((resolve, reject) => {
    link.addEventListener('load', resolve, {once: true});
    link.addEventListener('error', reject, {once: true});
    document.head.appendChild(link);
  });

  const xhr = new XMLHttpRequest();
  await new Promise((resolve, reject) => {
    xhr.onloadend = resolve;
    xhr.onloaderror = reject;
    xhr.open('GET', url);
    xhr.send();
  });
  verifyNumberOfResourceTimingEntries(url, 1);
  assert_equals(xhr.status, 200);
  assert_equals(xhr.responseText, dummyContent);
}, 'Make an XHR request after loading link rel=preload.');

</script>