// utils/storage.js

export default function () {
  return next => (reducer, initialState) => {
    const store = next(reducer, initialState);
    store.subscribe(() => {
      const state = store.getState();
      saveState(state);
    });
    return store;
  };
}

function saveState(state) {
  localStorage.setItem('app', state);
}

// app.js
import storageMiddleware from 'utils/storage';

const enhancer = compose(
  applyMiddleware(
    thunk,
  ),
  storageMiddleware(),
);