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.

• 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.

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

npm install react-native-mmkv

iOS installation is automatic, just run:

cd ios && pod install

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

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

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

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

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

MMKV.delete('user.name')

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

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

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)

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

MMKV.deleteAllKeys()

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

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.

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();
  },
};

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

import { MMKV } from 'react-native-mmkv';
import { configurePersistable } from 'mobx-persist-store';

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

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

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

MIT