localstorage-about-blank-partitioned-iframe.html

<!doctype html>
<meta charset="utf-8">
<script>
function getOrCreateID(key) {
  if (!localStorage.getItem(key)) {
    const newID = +new Date() + "-" + Math.random();
    localStorage.setItem(key, newID);
  }
  return localStorage.getItem(key);
}

window.addEventListener("load", () => {
  // if we have an opener, we know that we are loaded inside a cross-site
  // iframe (because we opened it ourselves).
  if (parent.opener) {
    const payload = {
      message: "cross-site window iframe loaded",
      userID: getOrCreateID("userID"),
    }
    parent.opener.postMessage(payload, parent.opener.origin);
  }
});

window.addEventListener("message", (e) => {
  if (e.data.command == "create ID") {
    getOrCreateID(e.data.key);

    // storage is set, call back to window.
    const payload = {
      message: "ID created",
      userID: localStorage.getItem("userID"),
    }

    e.source.postMessage(payload, e.source.origin);
  }

  if (e.data.command == "clearStorage") {
    localStorage.clear();
  }
});
</script>

chromium/third_party/blink/web_tests/external/wpt/webstorage/resources/localstorage-about-blank-partitioned-iframe.html