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MMKV


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.
  • 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

Set

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

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

Get

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

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

Delete

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

MMKV.delete('user.name')

Get all keys

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

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

Objects

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

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

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

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

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 { MMKV } from "react-native-mmkv";
import { Storage } from "redux-persist";

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

Contributing

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

License

MIT