In many web applications, it is common to store the state of the application in Redux. However, it is also important to persist this state so that it is not lost when the user refreshes the page or navigates away. One way to achieve this is by synchronizing the Redux state with the browser’s local storage or session storage.

Local storage and session storage are web storage APIs supported by modern browsers. They provide a simple key-value store that allows you to save data directly in the browser. The main difference between local storage and session storage is that local storage persists even after the browser is closed, while session storage is cleared once the browser session ends.

To synchronize the Redux state with the browser’s local storage or session storage, we can follow these steps:

Step 1: Create a Redux Middleware

We will create a Redux middleware that listens for specific actions and updates the storage accordingly. This middleware should be registered when creating the Redux store.

import { createAction } from 'redux-actions';

// Action type to trigger the persistence of state into storage
const PERSIST_STATE = 'PERSIST_STATE';

// Action creator that triggers the persistence action
export const persistState = createAction(PERSIST_STATE);

// Redux middleware
export const storageMiddleware = (store) => (next) => (action) => {
  if (action.type === PERSIST_STATE) {
    // Persist state to storage
    const state = store.getState();
    localStorage.setItem('reduxState', JSON.stringify(state));
  }

  return next(action);
};

Step 2: Add the Middleware to the Redux Store

Now, let’s add the created storageMiddleware to the Redux store.

import { createStore, applyMiddleware } from 'redux';
import { storageMiddleware } from './middlewares';

// Create your reducers and initialState
const reducers = // ...

// Create the Redux store
const store = createStore(
  reducers,
  applyMiddleware(storageMiddleware)
);

export default store;

Step 3: Load State from Storage on App Startup

To ensure that the persisted state is loaded from storage when the application starts, we can create an initialization function that retrieves the state from storage and dispatches it to the Redux store.

import { createAction } from 'redux-actions';

// Action type to trigger the loading of state from storage
const LOAD_STATE = 'LOAD_STATE';

// Action creator that triggers the loading action
export const loadState = createAction(LOAD_STATE);

// Initialization function
export const initializeApp = () => {
  return (dispatch) => {
    try {
      const serializedState = localStorage.getItem('reduxState');
      if (serializedState === null) {
        return undefined; // No stored state
      }
      const state = JSON.parse(serializedState);
      dispatch(loadState(state));
    } catch (error) {
      // Handle error
    }
  };
};

Step 4: Dispatch the Initialization Action

Finally, we need to dispatch the initializeApp action when the application starts. This can be done in the entry point file of your application.

import React from 'react';
import ReactDOM from 'react-dom';
import { Provider } from 'react-redux';
import store from './store';
import { initializeApp } from './actions';

// Dispatch the initialization action
store.dispatch(initializeApp());

ReactDOM.render(
  <Provider store={store}>
    // Your app components
  </Provider>,
  document.getElementById('root')
);

Conclusion

By synchronizing Redux state with the browser’s local storage or session storage, we can ensure that the state persists across page refreshes or even when the browser is closed. This provides an improved user experience and prevents data loss. Remember to handle exceptions and edge cases in your implementation to ensure robustness.

#Redux #LocalStorage