var eddystone = new Eddystone();
var beacon, service;
eddystone.request() // Scan for Eddystone beacons.
  .then((newBeacon) => {
    beacon = newBeacon;
    return beacon.connect(); // Connect to the Beacon's GATT service.
  })
  .then((newService) => {
    service = newService;
    return service.isLocked(); // Check if the beacon is locked.
  })
  .then((isLocked) => {
    if (isLocked) {
      return Promise.reject('The beacon is locked. Can\'t write new URL');
    }
    // Beacon's not locked. We can proceed with the recording of the new URL.
    // Keep in mind that the encoded URL must NOT be longer than 18 characters.
    return service.writeUrl('https://www.google.com');
  })
  .then(() => {
    beacon.disconnect();
    alert('OK!');
  });