ask for expo token and save to firebase

registerForPushNotifications = async () =>{//Get the current users id So you can post the token to the user in your databaseconst  currentUser = firebase.auth().currentUser.uidconst { status: existingStatus } = await Permissions.getAsync(Permissions.NOTIFICATIONS);let finalStatus = existingStatus;// only ask if permissions have not already been determined, because// iOS won't necessarily prompt the user a second time.if (existingStatus !== 'granted') {// Android remote notification permissions are granted during the app// install, so this will only ask on iOSconst { status } = await Permissions.askAsync(Permissions.NOTIFICATIONS);finalStatus = status;}// Stop here if the user did not grant permissionsif (finalStatus !== 'granted') {return;}// Get the token that uniquely identifies this devicetry{let token = await Notifications.getExpoPushTokenAsync();// POST the token to your backend server from where you can retrieve it to send push notifications.var updates = {}updates['/expoToken'] = tokenfirebase.database().ref('users').child(currentUser).update(updates)}catch(error){console.log(error)}}