fetch/stale-while-revalidate/stale-script.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>Tests Stale While Revalidate works for scripts</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/common/utils.js"></script>
<body>
<script>

const request_token = token();
const script_src = "./resources/stale-script.py?token=" + request_token;

// The script above will call report() via a uniquely generated ID on the
// subresource. If it is a cache hit, the ID will be the same and
// |last_modified_count| won't be incremented.
let last_modified;
let last_modified_count = 0;
function report(mod) {
  if (last_modified == mod)
    return;
  last_modified = mod;
  last_modified_count++;
}

let loadScript = async () => {
  let script = document.createElement("script");
  let script_loaded = new Promise(r => script.onload = r);
  script.src = script_src;
  document.body.appendChild(script);
  await script_loaded;
};

promise_test(async t => {
  await new Promise(r => window.onload = r);

  await loadScript();
  assert_equals(last_modified_count, 1, '(initial version loaded)');

  await loadScript();
  assert_equals(last_modified_count, 1, '(stale version loaded)');

  // Query the server again and again. At some point it must have received the
  // revalidation request. We poll, because we don't know when the revalidation
  // will occur.
  while(true) {
    await new Promise(r => step_timeout(r, 25));
    let response = await fetch(script_src + "&query");
    let count = response.headers.get("Count");
    if (count == '2')
      break;
  }

  await loadScript();
  assert_equals(last_modified_count, 2, '(revalidated version loaded)');

}, 'Cache returns stale resource');

</script>
</body>