Offline Persistence

Firebase apps naturally handle network interruptions, but you can explicitly enable disk persistence to allow data to survive app restarts and reboots, even without a connection.

1. Firestore Persistence (Web)

On web, persistence is not enabled by default. You must call enableIndexedDbPersistence.

import { getFirestore, enableIndexedDbPersistence } from "firebase/firestore";

const db = getFirestore();

enableIndexedDbPersistence(db).catch((err) => {
    if (err.code == 'failed-precondition') {
        // Multiple tabs open, persistence can only be enabled in one tab at a time.
        console.log("Persistence failed (multiple tabs)");
    } else if (err.code == 'unimplemented') {
        // The current browser does not support persistence.
        console.log("Persistence is not supported");
    }
});

2. How it Works

• Caching: Queries are served from the local cache when offline.
• Syncing: Once the device comes back online, local changes are sent to the server automatically.
• Metadata: You can check doc.metadata.fromCache to see if the data is live or local.

3. Realtime Database Persistence

For the Realtime Database, simple persistence is enabled like this:

firebase.database().goOffline(); // Manually manage state