Frontend Development: Where is Redux State Stored?

Redux, a popular state management library, is known for its centralized state management. But where is this state actually stored? Understanding the mechanics behind Redux can make it easier to use effectively.

What is the Redux State?

The Redux state, often simply referred to as the store, is a JavaScript object that contains the entire state of a Redux application. It's the single source of truth for any state that your app needs to maintain.

Here's a simplified example of what a Redux store might look like:

const store = {
  user: {
    name: 'John Doe',
    age: 25,
  },
  posts: [
    { id: 1, title: 'Post 1', content: 'Some content' },
    { id: 2, title: 'Post 2', content: 'Some more content' },
  ],
};

Where is the Redux State Stored?

The Redux state is stored in-memory in a JavaScript object within your application code. Redux does not persist the state between sessions by default, meaning if you refresh your application, your Redux store will be reinitialized.

Contrary to what some might believe, the Redux state is not stored in local storage or any other persistent storage by default, though it can be if you choose to add that functionality with middleware.

Using Middleware for Persistent State

There are Redux middleware options, such as redux-persist, that you can use if you want your Redux state to be stored persistently (e.g., in local storage).

Here's an example of how you can use redux-persist:

import { createStore } from 'redux';
import { persistStore, persistReducer } from 'redux-persist';
import storage from 'redux-persist/lib/storage'; // defaults to localStorage for web

const persistConfig = {
  key: 'root',
  storage,
};

const rootReducer = (state = {}, action) => { /*...*/ };

const persistedReducer = persistReducer(persistConfig, rootReducer);

const store = createStore(persistedReducer);
const persistor = persistStore(store);

This will automatically persist your store in local storage and rehydrate it when the user refreshes or reopens the page.

Conclusion

The Redux state is stored in-memory and does not persist across sessions by default. This means that the state is lost when the page is refreshed or the app is reloaded. However, middleware like redux-persist can be added to make the state persistent across sessions. Understanding where and how Redux state is stored can be critical for effectively managing your application's state.