Storage

React Native · Reference cheat sheet

📋 Overview

Persist data on device: AsyncStorage / MMKV for general prefs, SecureStore / Keychain for secrets, and the filesystem for files. Remember the store is per-install and can be cleared.

🔧 Core concepts

• AsyncStorage — async key/value strings; fine for small prefs.
• MMKV — fast sync-ish storage (via JSI); great for app state.
• SecureStore / Keychain — tokens, not large blobs.
• File system — expo-file-system for downloads/cache.
• Serialization — JSON.stringify / parse with versioned schemas.

💡 Examples

import AsyncStorage from "@react-native-async-storage/async-storage";

const KEY = "settings/v1";

export async function loadSettings<T>(fallback: T): Promise<T> {
  const raw = await AsyncStorage.getItem(KEY);
  if (!raw) return fallback;
  try {
    return JSON.parse(raw) as T;
  } catch {
    return fallback;
  }
}

export async function saveSettings<T>(value: T) {
  await AsyncStorage.setItem(KEY, JSON.stringify(value));
}

import * as SecureStore from "expo-secure-store";

await SecureStore.setItemAsync("session", token);
const token = await SecureStore.getItemAsync("session");

⚠️ Pitfalls

• Storing secrets in AsyncStorage.
• Unbounded growth — no eviction strategy for caches.
• Assuming storage survives reinstall or OS backup policies for secure items.

🔗 Related

• settings.md — preferences UX
• request.md — auth tokens
• clipboard.md — ephemeral data
• Expo/config.md — Expo modules