import { SharedNotificationDelegate } from '@nativescript/shared-notification-delegate';
...

SharedNotificationDelegate.addObserver({
    delegateUniqueKey: "myUniqueKey", // ensures uniqueness, if not set or is null/undefined, allows multiple of the same
    userNotificationCenterWillPresentNotificationWithCompletionHandler: (notificationCenter, notification, handler, stop, next) => {

        console.log("notification received by observer");
        // is this notification something I should handle?
        if (shouldHandleThis) {
            // do stuff
            // intercept it and show alert
            handler(UNNotificationPresentationOptions.Alert);
            return;
        }
        // not mine, next should handle
        next();
    }
});

interface DelegateObserver {
  userNotificationCenterDidReceiveNotificationResponseWithCompletionHandler?(
    center: UNUserNotificationCenter,
    response: UNNotificationResponse,
    completionHandler: () => void,
    next: () => void
  ): void

  userNotificationCenterOpenSettingsForNotification?(
    center: UNUserNotificationCenter,
    notification: UNNotification,
    stop: () => void,
    next: () => void
  ): void

  userNotificationCenterWillPresentNotificationWithCompletionHandler?(
    center: UNUserNotificationCenter,
    notification: UNNotification,
    completionHandler: (p1: UNNotificationPresentationOptions) => void,
    next: () => void
  ): void

  /**
   * if set to not null/undefined, will ensure only one is registered
   */
  delegateUniqueKey?: any
}