https://medium.com/javascript-in-plain-english/how-to-handle-and-design-the-startup-of-a-react-application-da779f3727e5

useFavoriteCountry.tsx

import AsyncStorage from "@react-native-community/async-storage";
import to from "await-to-js";
import { useCallback, useEffect, useState } from "react";

enum CountrySelectionStatus {
  Loading = "LOADING",
  NotChosen = "NOT_CHOSEN",
  Skipped = "SKIPPED",
}

enum AsyncStorageKeys {
  UserFavoriteCountry = "UserFavoriteCountry",
}

export interface UseFavoriteContext {
  favoriteCountry: string | CountrySelectionStatus;
  setFavoriteCountry: (country: string) => Promise<void>;
}

/**
 * Get and save user favorite information.
 *
 * @export
 * @returns {UseFavoriteContext}
 */
export function useFavoriteCountry(): UseFavoriteContext {
  const setFavoriteCountry = useCallback(async (countryCode: string | CountrySelectionStatus) => {
    await AsyncStorage.setItem(AsyncStorageKeys.UserFavoriteCountry, countryCode);

    setFavoriteCtx(prev => ({
      ...prev,
      favoriteCountry: countryCode,
    }));
  }, []);

  // State
  const [favoriteCtx, setFavoriteCtx] = useState<UseFavoriteContext>({
    favoriteCountry: CountrySelectionStatus.Loading,
    setFavoriteCountry,
  });

  // Read in memory data on load.
  useEffect(() => {
    async function initializeStateFromAsyncStorage() {
      const [err, favoriteCountry] = await to(AsyncStorage.getItem(AsyncStorageKeys.UserFavoriteCountry));
      if (err || favoriteCountry === CountrySelectionStatus.NotChosen) {
        setFavoriteCtx(prev => ({
          ...prev,
          favoriteCountry: CountrySelectionStatus.NotChosen,
        }));
        return;
      }
      setFavoriteCtx(prev => ({
        ...prev,
        favoriteCountry: favoriteCountry!,
      }));
    }
    initializeStateFromAsyncStorage();
  }, []);

  return favoriteCtx;
}