Notes on building a Local-First PWA with IndexedDB and Server-Sent Events (SSE)
When building a dealership inventory catalog for sales agents on showroom iPads, we realized standard network-on-every-filter setups were breaking the pace of sales conversations. Every loading spinner broke conversational flow.
We restructured the catalog around a local-first pattern: load the inventory once, keep it on the device, filter in memory, and use a light server signal to invalidate cache only when the inventory actually changes.
Upfront Payload for In-Memory Filtering: Instead of paginated API queries on every filter change (brand, price, mileage), we fetch the full vehicle inventory once.
Instant Rehydration via IndexedDB: To avoid startup latency on repeat visits, we persist the TanStack Query cache to IndexedDB.
Cheap Real-Time Invalidation via RxJS + SSE: To prevent stale data (e.g., sold/repriced cars) without burning serverless budget on polling, we use a single Server-Sent Events (SSE) connection.
Read the full article: https://blaze64.dev/logs/local-first-pwa