redux-persist

What is redux-persist?

redux-persist is a library that allows you to save the Redux store in persistent storage, such as local storage, session storage, or even custom storage engines. This helps in maintaining the state of the application across page reloads.

What are redux-persist's main functionalities?

Persisting Redux State

This feature allows you to persist the Redux state using a storage engine like local storage. The `persistReducer` function wraps your root reducer, and `persistStore` initializes the persistor.

const persistConfig = { key: 'root', storage }; const persistedReducer = persistReducer(persistConfig, rootReducer); const store = createStore(persistedReducer); const persistor = persistStore(store);

Rehydrating State

Rehydration is the process of loading the persisted state back into the Redux store when the application starts. This ensures that the state is restored to its previous state before the page was reloaded.

persistStore(store, null, () => { console.log('Rehydration complete'); });

Custom Storage Engines

You can use custom storage engines if the default local storage or session storage does not meet your requirements. This example shows how to create a noop storage engine for environments where local storage is not available.

import createWebStorage from 'redux-persist/lib/storage/createWebStorage'; const createNoopStorage = () => { return { getItem(_key) { return Promise.resolve(null); }, setItem(_key, value) { return Promise.resolve(value); }, removeItem(_key) { return Promise.resolve(); } }; }; const storage = typeof window !== 'undefined' ? createWebStorage('local') : createNoopStorage();

Other packages similar to redux-persist

redux-localstorage

redux-localstorage is another library that allows you to persist Redux state to local storage. It is similar to redux-persist but offers a more modular approach, allowing you to choose different storage adapters and serializers.

redux-persist-transform-encrypt

redux-persist-transform-encrypt is a transformer for redux-persist that encrypts your persisted state. This is useful if you need to store sensitive information securely. It works as an add-on to redux-persist, providing encryption capabilities.

redux-persist-cookie-storage

redux-persist-cookie-storage is a storage engine for redux-persist that uses cookies instead of local storage or session storage. This can be useful for server-side rendering or when you need to share state across different subdomains.

README

Redux Persist

Persist and rehydrate a redux store.

Quickstart

npm install redux-persist

Usage Examples:

1. Basic Usage
2. Nested Persists
3. Hot Module Replacement
4. Code Splitting [coming soon]

Basic Usage

Basic usage involves adding persistReducer and persistStore to your setup. IMPORTANT Every app needs to decide how many levels of state they want to "merge". The default is 1 level. Please read through the state reconciler docs for more information.

// configureStore.js

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

import rootReducer from './reducers'

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

const persistedReducer = persistReducer(persistConfig, rootReducer)

export default () => {
  let store = createStore(persistedReducer)
  let persistor = persistStore(store)
  return { store, persistor }
}

If you are using react, wrap your root component with PersistGate. This delays the rendering of your app's UI until your persisted state has been retrieved and saved to redux. NOTE the PersistGate loading prop can be null, or any react instance, e.g. loading={<Loading />}

import { PersistGate } from 'redux-persist/integration/react'

// ... normal setup, create store and persistor, import components etc.

const App = () => {
  return (
    <Provider store={store}>
      <PersistGate loading={null} persistor={persistor}>
        <RootComponent />
      </PersistGate>
    </Provider>
  );
};

API

Full API

persistReducer(config, reducer)

• arguments
  • config object
    • required config: key, storage
    • notable other config: whitelist, blacklist, version, stateReconciler, debug
  • reducer function
    • any reducer will work, typically this would be the top level reducer returned by combineReducers
• returns an enhanced reducer

persistStore(store, [config, callback])

• arguments
  • store redux store The store to be persisted.
  • config object (typically null)
  • callback function will be called after rehydration is finished.
• returns persistor object

persistor object

• the persistor object is returned by persistStore with the following methods:
  • .purge()
    • purges state from disk and returns a promise
  • .flush()
    • immediately writes all pending state to disk and returns a promise
  • .pause()
    • pauses persistence
  • .persist()
    • resumes persistence

State Reconciler

State reconcilers define how incoming state is merged in with initial state. It is critical to choose the right state reconciler for your state. There are three options that ship out of the box, let's look at how each operates:

1. hardSet (import hardSet from 'redux-persist/lib/stateReconciler/hardSet') This will hard set incoming state. This can be desirable in some cases where persistReducer is nested deeper in your reducer tree, or if you do not rely on initialState in your reducer.
   • incoming state: { foo: incomingFoo }
   • initial state: { foo: initialFoo, bar: initialBar }
   • reconciled state: { foo: incomingFoo } // note bar has been dropped
2. autoMergeLevel1 (default) This will auto merge one level deep. Auto merge means if the some piece of substate was modified by your reducer during the REHYDRATE action, it will skip this piece of state. Level 1 means it will shallow merge 1 level deep.
   • incoming state: { foo: incomingFoo }
   • initial state: { foo: initialFoo, bar: initialBar }
   • reconciled state: { foo: incomingFoo, bar: initialBar } // note incomingFoo overwrites initialFoo
3. autoMergeLevel2 (import autoMergeLevel2 from 'redux-persist/lib/stateReconciler/autoMergeLevel2') This acts just like autoMergeLevel1, except it shallow merges two levels
   • incoming state: { foo: incomingFoo }
   • initial state: { foo: initialFoo, bar: initialBar }
   • reconciled state: { foo: mergedFoo, bar: initialBar } // note: initialFoo and incomingFoo are shallow merged

Example

import hardSet from 'redux-persist/lib/stateReconciler/hardSet'

const persistConfig = {
  key: 'root',
  storage,
  stateReconciler: hardSet,
}

React Integration

Redux persist ships with react integration as a convenience. The PersistGate component is the recommended way to delay rendering until persistence is complete. It works in one of two modes:

1. loading prop: The provided loading value will be rendered until persistence is complete at which point children will be rendered.
2. function children: The function will be invoked with a single bootstrapped argument. When bootstrapped is true, persistence is complete and it is safe to render the full app. This can be useful for adding transition animations.

Blacklist & Whitelist

By Example:

// BLACKLIST
const persistConfig = {
  key: 'root',
  storage: storage,
  blacklist: ['navigation'] // navigation will not be persisted
};

// WHITELIST
const persistConfig = {
  key: 'root',
  storage: storage,
  whitelist: ['navigation'] // only navigation will be persisted
};

Nested Persists

Nested persist can be useful for including different storage adapters, code splitting, or deep filtering. For example while blacklist and whitelist only work one level deep, but we can use a nested persist to blacklist a deeper value:

import { combineReducers } from 'redux'
import { persistReducer } from 'redux-persist'
import storage from 'redux-persist/lib/storage'

import { authReducer, otherReducer } from './reducers'

const rootPersistConfig = {
  key: 'root',
  storage: storage,
  blacklist: ['auth']
}

const authPersistConfig = {
  key: 'auth',
  storage: storage,
  blacklist: ['somethingTemporary']
}

const rootReducer = combineReducers({
  auth: persistReducer(authPersistConfig, authReducer),
  other: otherReducer,
})

export default persistReducer(rootPersistConfig, rootReducer)

Migrations

persistReducer has a general purpose "migrate" config which will be called after getting stored state but before actually reconciling with the reducer. It can be any function which takes state as an argument and returns a promise to return a new state object.

Redux Persist ships with createMigrate, which helps create a synchronous migration for moving from any version of stored state to the current state version. [Additional information]

Transforms

Transforms allow you to customize the state object that gets persisted and rehydrated.

There are several libraries that tackle some of the common implementations for transforms.

• immutable - support immutable reducers
• compress - compress your serialized state with lz-string
• encrypt - encrypt your serialized state with AES
• filter - store or load a subset of your state
• filter-immutable - store or load a subset of your state with support for immutablejs
• expire - expire a specific subset of your state based on a property

When the state object gets persisted, it first gets serialized with JSON.stringify(). If parts of your state object are not mappable to JSON objects, the serialization process may transform these parts of your state in unexpected ways. For example, the javascript Set type does not exist in JSON. When you try to serialize a Set via JSON.stringify(), it gets converted to an empty object. Probably not what you want.

Below is a Transform that successfully persists a Set property, which simply converts it to an array and back. In this way, the Set gets converted to an Array, which is a recognized data structure in JSON. When pulled out of the persisted store, the array gets converted back to a Set before being saved to the redux store.

const myTransform = createTransform(
  // transform state on its way to being serialized and persisted.
  (inboundState, key) => {
    // convert mySet to an Array.
    return { ...inboundState, mySet: [...inboundState.mySet] };
  },
  // transform state being rehydrated
  (outboundState, key) => {
    // convert mySet back to a Set.
    return { ...outboundState, mySet: new Set(outboundState.mySet) };
  },
  // define which reducers this transform gets called for.
  { whitelist: ['someReducer'] }
);

The createTransform function takes three parameters.

1. An "inbound" function that gets called right before state is persisted.
2. An "outbound" function that gets called right before state is rehydrated.
3. Config.

Storage Engines

• localStorage import storage from 'redux-persist/lib/storage'
• sessionStorage import storageSession from 'redux-persist/lib/storage/session'
• AsyncStorage react-native import { AsyncStorage } from 'react-native'
• localForage recommended for web
• electron storage Electron support via electron store
• redux-persist-filesystem-storage react-native, to mitigate storage size limitations in android (#199, #284)
• redux-persist-node-storage for use in nodejs environments.
• redux-persist-sensitive-storage react-native, for sensitive information (uses react-native-sensitive-info).
• redux-persist-expo-securestore react-native, for sensitive information using Expo's SecureStore. Only available if using Expo SDK (Expo, create-react-native-app, standalone).
• redux-persist-fs-storage react-native-fs engine
• redux-persist-cookie-storage Cookie storage engine, works in browser and Node.js, for universal / isomorphic apps
• redux-persist-weapp-storage Storage engine for wechat mini program, also compatible with wepy
• redux-persist-webextension-storage Storage engine for browser (Chrome, Firefox) web extension storage
• @bankify/redux-persist-realm Storage engine for Realm database, you will need to install Realm first
• custom any conforming storage api implementing the following methods: setItem getItem removeItem. (NB: These methods must support promises)