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MIGRATE_FROM_ASYNC_STORAGE.md

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Migrate from AsyncStorage

Here's a migration script to copy all values from AsyncStorage to MMKV, and delete them from AsyncStorage afterwards.

storage.ts 
import AsyncStorage from '@react-native-async-storage/async-storage';
import {MMKV} from 'react-native-mmkv';

export const storage = new MMKV();

// TODO: Remove `hasMigratedFromAsyncStorage` after a while (when everyone has migrated)
export const hasMigratedFromAsyncStorage = storage.getBoolean(
  'hasMigratedFromAsyncStorage',
);

// TODO: Remove `hasMigratedFromAsyncStorage` after a while (when everyone has migrated)
export async function migrateFromAsyncStorage(): Promise<void> {
  console.log('Migrating from AsyncStorage -> MMKV...');
  const start = global.performance.now();

  const keys = await AsyncStorage.getAllKeys();

  for (const key of keys) {
    try {
      const value = await AsyncStorage.getItem(key);

      if (value != null) {
        if (['true', 'false'].includes(value)) {
          storage.set(key, value === 'true');
        } else {
          storage.set(key, value);
        }

        AsyncStorage.removeItem(key);
      }
    } catch (error) {
      console.error(
        `Failed to migrate key "${key}" from AsyncStorage to MMKV!`,
        error,
      );
      throw error;
    }
  }

  storage.set('hasMigratedFromAsyncStorage', true);

  const end = global.performance.now();
  console.log(`Migrated from AsyncStorage -> MMKV in ${end - start}ms!`);
}
App.tsx 
...
import { hasMigratedFromAsyncStorage, migrateFromAsyncStorage } from './storage';
...

export default function App() {
  // TODO: Remove `hasMigratedFromAsyncStorage` after a while (when everyone has migrated)
  const [hasMigrated, setHasMigrated] = useState(hasMigratedFromAsyncStorage);

  ...

  useEffect(() => {
    if (!hasMigratedFromAsyncStorage) {
      InteractionManager.runAfterInteractions(async () => {
        try {
          await migrateFromAsyncStorage()
          setHasMigrated(true)
        } catch (e) {
          // TODO: fall back to AsyncStorage? Wipe storage clean and use MMKV? Crash app?
        }
      });
    }
  }, []);

  if (!hasMigrated) {
    // show loading indicator while app is migrating storage...
    return (
      <View style={{ justifyContent: 'center', alignItems: 'center' }}>
        <ActivityIndicator color="black" />
      </View>
    );
  }

  return (
    <YourAppsCode />
  );
}