gem-hunter
Language: TypeScript
⚡️ The fastest key/value storage for React Native. ~30x faster than AsyncStorage!
| V4 Docs | old V3 Docs |
|---|
Important
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.
npm install react-native-mmkv react-native-nitro-modules cd ios && pod install
npx expo install react-native-mmkv react-native-nitro-modules npx expo prebuild
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.
import { createMMKV } from 'react-native-mmkv' export const storage = createMMKV()
This creates a new storage instance using the default MMKV storage ID (mmkv.default).
If you want to share MMKV data between your app and other apps or app extensions in the same group, open Info.plist and create an AppGroupIdentifier key with your app group's value. MMKV will then automatically store data inside the app group which can be read and written to from other apps or app extensions in the same group by making use of MMKV's multi processing mode.
See Configuring App Groups.
import { createMMKV } from 'react-native-mmkv' export const storage = createMMKV({ id: `user-${userId}-storage`, path: `${USER_DIRECTORY}/storage`, encryptionKey: 'hunter2', encryptionType: 'AES-256', mode: 'multi-process', readOnly: false, compareBeforeSet: false, })
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 separate 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)encryptionType: The MMKV instance's encryption/decryption algorithm. By default, AES-128 encryption will be used, but you can switch to AES-256 for advanced security.mode: The MMKV's process behaviour - when set to multi-process, the MMKV instance will assume data can be changed from the outside (e.g. App Clips, Extensions or App Groups).readOnly: Whether this MMKV instance should be in read-only mode. This is typically more efficient and avoids unwanted writes to the data if not needed. Any call to set(..) will throw.compareBeforeSet: Whether this MMKV instance will compare values for equality before writing them to disk. By default this is disabled, enabling it might improve performance if values are repeatedly written to disk, even if they are already persisted.storage.set('user.name', 'Marc') storage.set('user.age', 21) storage.set('is-mmkv-fast-asf', true)
const username = storage.getString('user.name') // 'Marc' const age = storage.getNumber('user.age') // 21 const isMmkvFastAsf = storage.getBoolean('is-mmkv-fast-asf') // true
const [username, setUsername] = useMMKVString('user.name') const [age, setAge] = useMMKVNumber('user.age') const [isMmkvFastAsf, setIsMmkvFastAsf] = useMMKVBoolean('is-mmkv-fast-asf')
// 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 const wasRemoved = storage.remove('user.name') // delete all keys storage.clearAll()
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) // { username: 'Marc', age: 21 }
// encrypt all data with a private key using AES-128 storage.encrypt('hunter2') // encrypt all data with a private key using AES-256 storage.encrypt('hunter2again', 'AES-256') // remove encryption storage.decrypt()
const buffer = new ArrayBuffer(3) const dataWriter = new Uint8Array(buffer) dataWriter[0] = 1 dataWriter[1] = 100 dataWriter[2] = 255 storage.set('someToken', buffer) const buffer = storage.getBuffer('someToken') console.log(buffer) // [1, 100, 255]
// get size of MMKV storage in bytes const size = storage.byteSize if (size >= 4096) { // clean unused keys and clear memory cache storage.trim() }
To import all keys and values from another MMKV instance, use importAllFrom(...):
const storage = createMMKV(...) const otherStorage = createMMKV(...) const importedCount = storage.importAllFrom(otherStorage)
To check if an MMKV instance exists, use existsMMKV(...):
import { existsMMKV } from 'react-native-mmkv' const exists = existsMMKV('my-instance')
To delete an MMKV instance, use deleteMMKV(...):
import { deleteMMKV } from 'react-native-mmkv' const wasDeleted = deleteMMKV('my-instance')
By default, MMKV logs at Debug level in debug builds and Warning level in release builds. You can override this at build time to control the verbosity of MMKV's native logs.
| Value | Level |
|---|---|
| 0 | Debug |
| 1 | Info |
| 2 | Warning |
| 3 | Error |
| 4 | None |
Set MMKV_logLevel in your app's android/gradle.properties:
MMKV_logLevel=4Set $MMKVLogLevel in your app's ios/Podfile, then run pod install:
$MMKVLogLevel = 4
Or use an environment variable during pod install:
MMKV_LOG_LEVEL=4 pod install
A mocked MMKV instance is automatically used when testing with Jest or Vitest, so you will be able to use createMMKV() as per normal in your tests. Refer to example/__tests__/MMKV.harness.ts for an example using Jest.
If a user chooses to disable LocalStorage in their browser, the library will automatically provide a limited in-memory storage as an alternative. However, this in-memory storage won't persist data, and users may experience data loss if they refresh the page or close their browser. To optimize user experience, consider implementing a suitable solution within your app to address this scenario.
Use @rozenite/mmkv-plugin to debug your MMKV storage using Rozenite.
Use reactotron-react-native-mmkv to automatically log writes to your MMKV storage using Reactotron. See the docs for how to setup this plugin with Reactotron.
Join the Margelo Community Discord to chat about react-native-mmkv or other Margelo libraries.
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.
See the contributing guide to learn how to contribute to the repository and the development workflow.
MIT