IonicでのFirebaseによるプッシュ通知用のトークンを取得するサンプル。

app.module.ts

// src/app/app.module.ts
import { Firebase } from '@ionic-native/firebase';
@NgModule({
//...
providers: [
  Firebase,
],
//...
})
export class AppModule {}

sample.ts

// src/pages/sample/sample.ts
// import省略
@IonicPage()
@Component({
  selector: 'page-sample',
  templateUrl: 'sample.html',
})
export class SamplePage {
  constructor(public platform: Platform, private firebase: Firebase,) {
    this.platform.ready().then(() => {
      
      if (this.platform.is('ios')) {
        this.getPushTokenIOS()
          .pipe(
            mergeMap(token => this.requestDevice(token))
          ).subscribe({
          next: response => {
            // newsトピックを購読する
            this.firebase.subscribe('news')
          },
          error: error => {
            console.error(error);
          }
          });
      }

      if (this.platform.is('android')) {
        this.getPushTokenAndroid()
          .pipe(
            mergeMap(token => this.requestDevice(token))
          ).subscribe({
          next: response => {
            // newsトピックを購読する
            this.firebase.subscribe('news')
          },
          error: error => {
            console.error(error);
          }
        });
      }
    })
  }

  getPushTokenIOS(): Observable<string|boolean> {
    return this.hasPushPermission()
      .pipe(
        mergeMap((permission) => {
          if (permission.isEnabled) {
            return this.getPushToken();
          } else {
            return this.grantPushPermission()
              .pipe(
                mergeMap((grant) => {
                  return this.getPushToken();
                }),
                catchError(error => {
                  return of(false);
                })
              );
          }
        }),
      )
  }

  getPushTokenAndroid(): Observable<string|boolean> {
    return this.hasPushPermission()
      .pipe(
        mergeMap(permission => {
          if (permission.isEnabled) {
            return this.getPushToken();
          } else {
            return of(false);
          }
        })
      )
  }

  private requestDevice(token: string): Observable<any> {
    if (typeof token === 'string') {
      // デバイストークンをサーバに保存する
      // return Observable<any>
    } else {
      return _throw('push token get error');
    }
  }

  private hasPushPermission(): Observable<{ isEnabled: boolean; }> {
    return fromPromise(this.firebase.hasPermission());
  }
  private grantPushPermission(): Observable<any> {
    return fromPromise(this.firebase.grantPermission());
  }
  private getPushToken(): Observable<any> {
    return fromPromise(this.firebase.getToken());
  }
}