PWA, Offline Mode, and IndexedDB: Reliable Web Apps Beyond the Tab
Progressive Web Apps can survive flaky networks when you design caching, sync, and conflict resolution deliberately. This is our playbook for offline-capable products.
Ali Mortazavi
Founder, Paradise Code
When Offline Actually Matters
Field sales, warehouse scanning, event apps, and education in low-connectivity regions benefit from offline-first or offline-tolerant designs. Marketing sites rarely need IndexedDB.
Define offline scope: read-only catalog, draft forms, queued actions, or full CRUD with sync. Scope drives storage size, conflict rules, and testing effort.
Users expect honesty: show connectivity status, last synced time, and what will happen to pending changes. Silent failure erodes trust.
Service Worker Strategy
Cache static assets with a versioned precache list on install. Use stale-while-revalidate for shell resources. Do not cache API responses blindly — stale prices and permissions are dangerous.
Network-first for auth and user-specific JSON; cache-first for immutable assets. Document strategies per route in the service worker source.
Update flow: notify users when a new version is available; skipWaiting with care so you do not interrupt in-progress forms.
IndexedDB Data Modeling
Use a thin wrapper — Dexie, idb — not raw IndexedDB callbacks. Define stores, indexes, and migrations like server schema.
Store normalized records with typed IDs. Embeddings work for read performance but complicate partial updates.
Cap storage growth: prune old drafts, LRU for media blobs, and warn before quota errors on mobile Safari.
Sync and Conflict Resolution
Queue mutations locally with client-generated IDs and timestamps. Replay on reconnect with idempotency keys server-side.
Conflicts: last-write-wins is simple but lossy. Prefer domain rules — server wins on inventory, merge on notes — and surface conflicts to users when automatic resolution is unsafe.
Background Sync API helps when supported; fallback to retry on online event and visibility change.
UX and Testing
Optimistic UI for queued actions with clear pending state. Allow edit and cancel before sync completes.
Test with Chrome offline throttling, airplane mode on devices, and Playwright network conditions. Unit tests alone miss service worker edge cases.
Lighthouse PWA checks are a baseline, not proof of reliable offline business logic.
Production Considerations
HTTPS required. Manifest and icons for install prompts where product strategy wants home-screen presence.
Security: treat offline data as sensitive — encrypt at rest for high-risk fields if platform allows, clear on logout.
PWA with IndexedDB delivers real value when offline scope is narrow, sync is explicit, and UX is transparent. Paradise Code builds these layers only when connectivity pain is validated user research, not speculation.
Insights
Need these ideas implemented in your product?
Paradise Code supports you from consult to full delivery.