notification.js

import { Notifications } from "expo";
import * as Permissions from 'expo-permissions'



    async function registerForPushNotificationsAsync() {
        const { 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 iOS
            const { status } = await Permissions.askAsync(Permissions.NOTIFICATIONS);
            finalStatus = status;
          }
          
          // Stop here if the user did not grant permissions
          if (finalStatus !== "granted") {
            //  Alert.alert('Please enable notification');
            return;
          }
          
          // Get the token that uniquely identifies this device
          let token = await Notifications.getExpoPushTokenAsync();
           var fcm = '' + token;
         
          console.log("*****************"+fcm);
        }



    const asyncFunc = () => {
        return new Promise((resolve, reject) => {
           
            registerForPushNotificationsAsync().then(
                resolve("okkkkkk")
            )

        })
    }
    
    export default asyncFunc