third_party/blink/web_tests/external/wpt/feature-policy/resources/feature-policy-wakelock.html

<script>
"use strict";

Promise.resolve().then(async () => {
  // On success, WakeLock.request() returns a promise that never resolves. To
  // prevent a timeout, abort it with an AbortController and use the different
  // DOMExceptions we get to determine if this worked or not.
  const controller = new AbortController();
  const wakeLock = WakeLock.request("screen", { signal: controller.signal });
  wakeLock.catch(e => {
    if (e.name == "AbortError") {
      // We stopped due to the call to AbortController.abort(), so we did manage
      // to get the lock.
      window.parent.postMessage({ enabled: true }, "*");
    } else if (e.name == "NotAllowedError") {
      // This means requesting the lock failed.
      window.parent.postMessage({ enabled: false }, "*");
    } else {
      // We should not really hit this branch.
      window.parent.postMessage({ enabled: false }, "*");
    }
  });
  controller.abort();
});
</script>