react-native-mmkv/src/createMMKV/createMockMMKV.ts

⚡️ The fastest key/value storage for React Native.

import type { MMKV } from '../specs/MMKV.nitro'
import type { Configuration } from '../specs/MMKVFactory.nitro'

/**
 * Mock MMKV instance when used in a Jest/Test environment.
 */
export function createMockMMKV(
  config: Configuration = { id: 'mmkv.default' }
): MMKV {
  const storage = new Map<string, string | boolean | number | ArrayBuffer>()
  const listeners = new Set<(key: string) => void>()

  const notifyListeners = (key: string) => {
    listeners.forEach((listener) => {
      listener(key)
    })
  }

  return {
    id: config.id,
    get length(): number {
      return storage.size
    },
    get size(): number {
      return this.byteSize
    },
    get byteSize(): number {
      // estimate - assumes UTF8
      return JSON.stringify(storage).length
    },
    isReadOnly: false,
    isEncrypted: false,
    clearAll: () => {
      const keysBefore = storage.keys()
      storage.clear()
      // Notify all listeners for all keys that were cleared
      for (const key of keysBefore) {
        notifyListeners(key)
      }
    },
    remove: (key) => {
      const deleted = storage.delete(key)
      if (deleted) {
        notifyListeners(key)
      }
      return deleted
    },
    set: (key, value) => {
      if (key === '') throw new Error('Cannot set a value for an empty key!')
      storage.set(key, value)
      notifyListeners(key)
    },
    getString: (key) => {
      const result = storage.get(key)
      return typeof result === 'string' ? result : undefined
    },
    getNumber: (key) => {
      const result = storage.get(key)
      return typeof result === 'number' ? result : undefined
    },
    getBoolean: (key) => {
      const result = storage.get(key)
      return typeof result === 'boolean' ? result : undefined
    },
    getBuffer: (key) => {
      const result = storage.get(key)
      return result instanceof ArrayBuffer ? result : undefined
    },
    getAllKeys: () => Array.from(storage.keys()),
    contains: (key) => storage.has(key),
    recrypt: () => {
      console.warn('Encryption is not supported in mocked MMKV instances!')
    },
    encrypt: () => {
      console.warn('Encryption is not supported in mocked MMKV instances!')
    },
    decrypt: () => {
      console.warn('Encryption is not supported in mocked MMKV instances!')
    },
    trim: () => {
      // no-op
    },
    name: 'MMKV',
    dispose: () => {},
    equals: () => {
      return false
    },
    addOnValueChangedListener: (listener) => {
      listeners.add(listener)
      return {
        remove: () => {
          listeners.delete(listener)
        },
      }
    },
    importAllFrom: (other) => {
      const keys = other.getAllKeys()
      let imported = 0
      for (const key of keys) {
        const data = other.getBuffer(key)
        if (data != null) {
          storage.set(key, data)
          imported++
        }
      }
      return imported
    },
  }
}