code: function urlB64ToUint8Array(base64String) {
      const padding = '='.repeat((4 - base64String.length % 4) % 4);
      const base64 = (base64String + padding)
          .replace(/\-/g, '+')
          .replace(/_/g, '/');
  
      const rawData = self.atob(base64);
      const outputArray = new Uint8Array(rawData.length);
  
      for (let i = 0; i < rawData.length; ++i) {
          outputArray[i] = rawData.charCodeAt(i);
      }
      return outputArray;
  }
docs: Helper method to convert the VAPID key to a UInt8 array and supply it to applicationServerKey.