react-native-mmkv/src/createMMKV.ts

The fastest key/value storage for React Native. ~30x faster than AsyncStorage! Works on Android, iOS and Web.

import { NativeModules, Platform } from 'react-native';
import type { MMKVConfiguration, NativeMMKV } from 'react-native-mmkv';

// global func declaration for JSI functions
declare global {
  function mmkvCreateNewInstance(configuration: MMKVConfiguration): NativeMMKV;
  function nativeCallSyncHook(): unknown;
}

// Root directory of all MMKV stores
const ROOT_DIRECTORY: string | null = null;

export const createMMKV = (config: MMKVConfiguration): NativeMMKV => {
  // Check if the constructor exists. If not, try installing the JSI bindings.
  if (global.mmkvCreateNewInstance == null) {
    // Get the native MMKV ReactModule
    const MMKVModule = NativeModules.MMKV;
    if (MMKVModule == null) {
      let message =
        'Failed to create a new MMKV instance: The native MMKV Module could not be found.';
      message +=
        '\n* Make sure react-native-mmkv is correctly autolinked (run `npx react-native config` to verify)';
      if (Platform.OS === 'ios' || Platform.OS === 'macos') {
        message += '\n* Make sure you ran `pod install` in the ios/ directory.';
      }
      if (Platform.OS === 'android') {
        message += '\n* Make sure gradle is synced.';
      }
      // check if Expo
      const ExpoConstants =
        NativeModules.NativeUnimoduleProxy?.modulesConstants?.ExponentConstants;
      if (ExpoConstants != null) {
        if (ExpoConstants.appOwnership === 'expo') {
          // We're running Expo Go
          throw new Error(
            'react-native-mmkv is not supported in Expo Go! Use EAS (`expo prebuild`) or eject to a bare workflow instead.'
          );
        } else {
          // We're running Expo bare / standalone
          message += '\n* Make sure you ran `expo prebuild`.';
        }
      }

      message += '\n* Make sure you rebuilt the app.';
      throw new Error(message);
    }

    // Check if we are running on-device (JSI)
    if (global.nativeCallSyncHook == null || MMKVModule.install == null) {
      throw new Error(
        'Failed to create a new MMKV instance: React Native is not running on-device. MMKV can only be used when synchronous method invocations (JSI) are possible. If you are using a remote debugger (e.g. Chrome), switch to an on-device debugger (e.g. Flipper) instead.'
      );
    }

    // Call the synchronous blocking install() function
    const result = MMKVModule.install(ROOT_DIRECTORY);
    if (result !== true)
      throw new Error(
        `Failed to create a new MMKV instance: The native MMKV Module could not be installed! Looks like something went wrong when installing JSI bindings: ${result}`
      );

    // Check again if the constructor now exists. If not, throw an error.
    if (global.mmkvCreateNewInstance == null)
      throw new Error(
        'Failed to create a new MMKV instance, the native initializer function does not exist. Are you trying to use MMKV from different JS Runtimes?'
      );
  }

  return global.mmkvCreateNewInstance(config);
};