Offline-First Design

Also Known As

TL;DR

Explanation

Offline-first assumes the network is unreliable — store everything locally first, then sync to the server when connectivity is available. Technologies: IndexedDB (client-side structured storage), Service Worker (intercept requests and serve from cache), Background Sync API (defer network requests until online), CRDTs (Conflict-free Replicated Data Types) for conflict-free merging. Patterns: optimistic updates (show change immediately, sync in background), conflict resolution (last-write-wins, server-wins, or manual merge), and sync queue (pending operations stored and retried).

Common Misconception

Why It Matters

Common Mistakes

• No conflict resolution strategy — concurrent offline edits from multiple devices corrupt data.
• Storing sensitive data in IndexedDB without encryption — IndexedDB is not encrypted by default.
• No user feedback on sync status — users need to know when their data is saved vs pending sync.
• Offline-first for real-time features — chat and live collaboration require constant connectivity.

Code Examples

// No offline support — data lost when network drops:
async function saveNote(note) {
    await fetch('/api/notes', {
        method: 'POST',
        body: JSON.stringify(note),
    });
    // If fetch fails: error, data lost, user frustrated
}

// Offline-first: save locally, sync in background:
async function saveNote(note) {
    const db = await openDB('notes-store', 1);
    await db.put('notes', { ...note, synced: false }); // Save locally first
    showUI('Saved locally');

    if (navigator.onLine) {
        await syncToServer(note);
        await db.put('notes', { ...note, synced: true });
        showUI('Synced');
    } else {
        // Background Sync: retry when online:
        await navigator.serviceWorker.ready.then(sw =>
            sw.sync.register('sync-notes')
        );
    }
}

References

• ↗ https://offlinefirst.org/

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