fcm.onNotification() how to make it synchronous?

I have to show some content based on fcm data what i fetch but the problem is it’s taking time to fetch data from notification mean while it’s navigating to some other page.I have to wait until fcm data fetched properly.

this.fcm.onNotification().subscribe(data => {
                   //show offers according to notification data
               //no fcm data go to offers page show old offers which are in nativestorage


now the problem is above method triggers when there is notification data other wise it’s not gonna trigger at all.

how should i handle this case??