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pwa-offline-sync

Skill2 starsChanged 12 days agoMITView on GitHub

Design Cache Storage + IndexedDB strategy and sync queue. Use this skill when building service workers, implementing caching strategies, or investigating offline bugs — even if they just say "make it work offline" or "add caching". Generic pattern for any offline-first application. Not for lifecycle-management.

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SKILL.md

PWA Offline Sync

Purpose: design, implement, and validate offline/PWA behavior (service worker, caches, IndexedDB, sync queue).

When to Use

  • Editing service worker, cache strategies, or sync orchestration.
  • Touching IndexedDB schema, permission caching, or zombie detection.
  • Investigating offline bugs or data conflicts.

Workflow

  1. Assess entity rules -- confirm table of offline-first entities + conflict strategy.
  2. Plan caches -- map static/assets/data to Cache Storage policies (cache-first vs stale-while-revalidate vs network-first).
  3. IndexedDB schema -- define stores for progress, annotations, sync queue, permission cache; version migrations carefully.
  4. Service worker -- implement install/activate/fetch with trace logging, offline fallback page, and error handling.
  5. Sync manager -- queue writes locally, dedupe via mutation IDs, replay when online, implement exponential backoff + zombie detection.
  6. Testing -- simulate offline/online in E2E tests; unit-test queue reducers; verify revoked access is blocked after reconnect.

Checklist

  • Cache + DB version numbers bumped intentionally (no silent clears).
  • Headers sent even when offline data queued.
  • Zombie detection notifies user + stops further reads upon revocation.
  • Service worker cleans up old caches.
  • Memory-safe listeners (remove event handlers when replaced).

See Also

  • lifecycle-management — Resource cleanup and error handling
  • css-render-performance — CSS render performance optimization

Rationalizations

RationalizationReality
"Cache-first is always the best strategy"Different data requires different strategies; stale-while-revalidate or network-first may be more appropriate.
"Sync queue is overkill for our simple app"Even simple apps need conflict resolution when offline writes collide with server state.
"Zombie detection is too complex to implement"Without it, revoked users can continue reading cached data indefinitely.

Red Flags

  • Using a single cache strategy for all data types
  • Not implementing zombie detection for revoked access
  • Forgetting to bump cache/DB version numbers on schema changes

References

  • references/offline-strategies.md - Offline-first architecture patterns
  • references/sync-queue.md - Sync queue design and conflict resolution

Voice & Context

  • Default: professional + blog
  • Reference: voice-profiles skill for definitions and auto-detection.

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