storeWithOffline.js

function isNetworkConnected(): Promise<boolean> {
  if (Platform.OS === 'ios') {
    return new Promise(resolve => {
      const handleFirstConnectivityChangeIOS = isConnected => {
        NetInfo.isConnected.removeEventListener(
          'change',
          handleFirstConnectivityChangeIOS,
        );
        resolve(isConnected);
      };
      NetInfo.isConnected.addEventListener(
        'change',
        handleFirstConnectivityChangeIOS,
      );
    });
  }

  return NetInfo.isConnected.fetch();
}

const networkMiddleware = createNetworkMiddleware();

export default function configureStore(): Promise<Store> {
  return new Promise((resolve: (arg: Store) => void) => {
    let nCalls = 0;
    let store;
    // resolver() will resolve the promise with the store
    // After rehydration and initial connection detection happens
    function resolver() {
      nCalls += 1;
      if (nCalls === 2) {
        resolve(store);
      }
    }
    
    store = createStore(
      rootReducer,
      undefined,
      compose(
        applyMiddleware(networkMiddleware),
        autoRehydrate(),
      ),
    );

    isNetworkConnected().then(isConnected => {
      store.dispatch({
        type: '@@network-connectivity/CONNECTION_CHANGE',
        payload: isConnected,
      });
      resolver();
    });

    persistStore(
      store,
      {
        storage: AsyncStorage,
        debounce: 500,
      },
      () => resolver(),
    );
  });
}