requestPermission for web push notifications

requestPermissionForWebPush.txt

function requestPermission() {
  return new Promise((resolve, reject) => {
    const permissionResult = Notification.requestPermission((result) => {
      // Handling deprecated version with callback.
      resolve(result);
    });

    if (permissionResult) {
      permissionResult.then(resolve, reject);
    }
  })
  .then((permissionResult) => {
    if (permissionResult !== 'granted') {
      throw new Error('Permission not granted.');
    }
  });
}