Notifications.js

import { Push, PushObject, PushOptions } from '@ionic-native/push';

constructor(private push: Push) { }

...


// comprobamos los permisos
this.push.hasPermission()
  .then((res: any) => {

    if (res.isEnabled) {
      console.log('We have permission to send push notifications');
    } else {
      console.log('We do not have permission to send push notifications');
    }

  });

// inicializamos la configuración para android y ios
const options: PushOptions = {
   android: {
       senderID: 'SENDER_ID'
   },
   ios: {
       senderID: 'SENDER_ID'//si no lo pones, se generará un token para APNS
       alert: 'true',
       badge: true,
       sound: 'false'
   },
   windows: {}
};

const pushObject: PushObject = this.push.init(options);

pushObject.on('notification').subscribe((notification: any) => {
  //aquí recibimos las notificaciones de firebase
});

pushObject.on('registration').subscribe((registration: any) => {
    const registrationId = registration.registrationId;
    //registrationId lo debes guardar en mysql o similar para reutilizar
});

pushObject.on('error').subscribe(error => {
    console.error('Error with Push plugin', error)
});