MMKV

The fastest key/value storage for React Native.

• 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 easily use MMKV inside your React Native applications. It provides fast and direct bindings to the native C++ library which are accessible through a simple JS API.

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++
• ~30x faster than AsyncStorage
• Uses JSI instead of the "old" Bridge
• iOS, Android and Web support
• Easy to use React Hooks API

Sponsors

react-native-mmkv is sponsored by getstream.io.
Try the React Native Chat tutorial 💬

Benchmark

StorageBenchmark compares popular storage libraries against each other by reading a value from storage for 1000 times:

MMKV vs other storage libraries: Reading a value from Storage 1000 times.
Measured in milliseconds on an iPhone 11 Pro, lower is better.

Installation

React Native

yarn add react-native-mmkv
cd ios && pod install

Expo

expo install react-native-mmkv
expo prebuild

Usage

Create a new instance

To create a new instance of the MMKV storage, use the MMKV constructor. It is recommended that you re-use this instance throughout your entire app instead of creating a new instance each time, so export the storage object.

Default

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

export 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'

export const storage = new MMKV({
  id: `user-${userId}-storage`,
  path: `${USER_DIRECTORY}/storage`,
  encryptionKey: 'hunter2'
})

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. (required if path or encryptionKey fields are specified, otherwise defaults to: '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 (documentation: iOS / Android)
• 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. (documentation: iOS / Android)

Set

storage.set('user.name', 'Marc')
storage.set('user.age', 21)
storage.set('is-mmkv-fast-asf', true)

Get

const username = storage.getString('user.name') // 'Marc'
const age = storage.getNumber('user.age') // 21
const isMmkvFastAsf = storage.getBoolean('is-mmkv-fast-asf') // true

Keys

// checking if a specific key exists
const hasUsername = storage.contains('user.name')

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

// delete a specific key + value
storage.delete('user.name')

// delete all keys
storage.clearAll()

Objects

const user = {
  username: 'Marc',
  age: 21
}

// Serialize the object into a JSON string
storage.set('user', JSON.stringify(user))

// Deserialize the JSON string into an object
const jsonUser = storage.getString('user') // { 'username': 'Marc', 'age': 21 }
const userObject = JSON.parse(jsonUser)

Encryption

// encrypt all data with a private key
storage.recrypt('hunter2')

// remove encryption
storage.recrypt(undefined)

Buffers

storage.set('someToken', new Uint8Array([1, 100, 255]))
const buffer = storage.getBuffer('someToken')
console.log(buffer) // [1, 100, 255]

Testing with Jest

A mocked MMKV instance is automatically used when testing with Jest, so you will be able to use new MMKV() as per normal in your tests. Refer to example/test/MMKV.test.ts for an example.

Documentation

• Hooks
• Value-change Listeners
• Migrate from AsyncStorage
• Using MMKV with redux-persist
• Using MMKV with mobx-persist-storage
• Using MMKV with mobx-persist
• Using MMKV with zustand persist-middleware
• Using MMKV with jotai
• How is this library different from react-native-mmkv-storage?

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.

Debugging

Use flipper-plugin-react-native-mmkv to debug your MMKV storage using Flipper. You can also simply console.log an MMKV instance.

Adopting at scale

react-native-mmkv is provided as is, I work on it in my free time.

If you're integrating react-native-mmkv in a production app, consider funding this project and contact me to receive premium enterprise support, help with issues, prioritize bugfixes, request features, help at integrating react-native-mmkv, and more.

Contributing

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

License

MIT