MMKV is an efficient, small mobile key-value storage framework developed by WeChat.

See Tencent/MMKV for more information

react-native-mmkv is a library that allows you to use MMKV inside your React Native applications.

Features

• Get and set strings, booleans and numbers
• Fully synchronous calls, no async/await, no Promises, no Bridge.
• Encryption support (secure storage)
• Multiple instances support (separate user-data with global data)
• Customize storage location
• High performance because everything is written in C++ (even the JS functions have C++ bodies!)
• ~30x faster than AsyncStorage
• Uses JSI instead of the "old" Bridge

Fun fact: since all the JS functions have C++ implementations, you can also directly call them in reanimated worklets, Vision Camera frame processors or custom threads using react-native-multithreading.

Benchmark

AsyncStorage vs MMKV: Reading a value from Storage 1000 times.
Measured in milliseconds on an iPhone 8, lower is better.

Installation

npm install react-native-mmkv

iOS

iOS installation is automatic, just run:

cd ios && pod install

Android

To correctly initialize MMKV on Android, please follow the Installation guide.

Usage

Create a new instance

To create a new instance of the MMKV storage, use the MMKV constructor.

Default

import { MMKV } from 'react-native-mmkv'

const storage = new MMKV()

This creates a new storage instance using the default MMKV storage ID (mmkv.default).

Customize

import { MMKV } from 'react-native-mmkv'

const storage = new MMKV({
  id: `user-${userId}-storage`,
  path: USER_DIRECTORY + '/storage',
  encryptionKey: 'some-encryption-key'
})

This creates a new storage instance using a custom MMKV storage ID. By using a custom storage ID, your storage is separated from the default MMKV storage of your app.

The following values can be configured:

• id: The MMKV instance's ID. If you want to use multiple instances, use different IDs. For example, you can separte the global app's storage and a logged-in user's storage. (default: 'mmkv.default')
• path: The MMKV instance's root path. By default, MMKV stores file inside $(Documents)/mmkv/. You can customize MMKV's root directory on MMKV initialization
• encryptionKey: The MMKV instance's encryption/decryption key. By default, MMKV stores all key-values in plain text on file, relying on iOS's/Android's sandbox to make sure the file is encrypted. Should you worry about information leaking, you can choose to encrypt MMKV.

Set

storage.set('user.name', 'Marc')
storage.set('user.age', 20)
storage.set('is-mmkv-fast-asf', true)

Get

const username = storage.getString('user.name') // 'Marc'
const age = storage.getNumber('user.age') // 20
const isMmkvFastAsf = storage.getBoolean('is-mmkv-fast-asf') // true

Delete

storage.delete('user.name')

Get all keys

const keys = storage.getAllKeys() // ['user.name', 'user.age', 'is-mmkv-fast-asf']

Objects

const user = {
  username: 'Marc',
  age: 20
}

storage.set('user', JSON.stringify(user))

const jsonUser = storage.getString('user') // { 'username': 'Marc', 'age': 20 }
const userObject = JSON.parse(jsonUser)

Delete all keys

storage.deleteAllKeys()

Migrate from AsyncStorage

See #52 for instructions on how to safely migrate your existing AsyncStorage database to MMKV.

Limitations

As the library uses JSI for synchronous native methods access, remote debugging (e.g. with Chrome) is no longer possible. Instead, you should use Flipper.

redux-persist

If you want to use MMKV with redux-persist, create the following storage object:

import { Storage } from 'redux-persist';

// Unfortunately redux-persist expects Promises,
// so we have to wrap our sync calls with Promise resolvers/rejecters
export const reduxStorage: Storage = {
  setItem: (key, value) => {
    storage.set(key, value);
    return Promise.resolve(true);
  },
  getItem: (key) => {
    const value = storage.getString(key);
    return Promise.resolve(value);
  },
  removeItem: (key) => {
    storage.delete(key);
    return Promise.resolve();
  },
};

mobx-persist-store

If you want to use MMKV with mobx-persist-store, create the following storage object:

import { configurePersistable } from 'mobx-persist-store';

configurePersistable({
  storage: {
    setItem: (key, data) => storage.set(key, data),
    getItem: (key) => storage.getString(key),
    removeItem: (key) => storage.delete(key),
  },
});

For more information, check out kanzitelli/rnn-starter.

Contributing

See the contributing guide to learn how to contribute to the repository and the development workflow.

License

MIT