Building Offline-First Web Apps with Service Workers and IndexedDB
Users expect apps to work everywhere — on airplanes, in subway tunnels, and in areas with spotty coverage. Offline-first architecture makes this possible for web apps.
The Offline-First Stack
–
Service Worker: Intercepts network requests, serves cached responses
–
IndexedDB: Client-side database for structured data
–
Background Sync: Queues mutations for when connectivity returns
–
Cache API: Stores static assets and API responses
Caching Strategies
Cache-first for static assets (CSS, JS, images). Network-first for API data that should be fresh. Stale-while-revalidate for content that can be slightly outdated.
Conflict Resolution
When the same record is modified offline on two devices, you need a conflict resolution strategy. Last-write-wins is simple but lossy. CRDTs (Conflict-free Replicated Data Types) merge changes automatically but add complexity. For most apps, operational transformation with a server-side merge function is the practical middle ground.