Service Worker–Based Persistent Prefetch Cache

[hoangsonww]

Summary
Introduce a service worker layer to persist GhostIO’s prefetched data beyond the in-memory cache. This allows cached API responses to survive page reloads, browser restarts, and offline usage.

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Why

• Current GhostIO caching is in-memory only (lost on reload).
• SPAs and dashboards often reload or navigate across routes → prefetched data is discarded.
• Developers want persistent, offline-ready prefetching (PWA-style).
• Aligns with GhostIO’s goal of improving UX speed + reliability.

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Scope (MVP)

1. Service Worker Integration

   • Register a service worker that listens for GhostIO-prefetched requests.
   • Store prefetched responses in the Cache Storage API.

2. Persistent Cache Retrieval

   • When ghost.get(url) is called:

     • First check in-memory cache.
     • If not found, check service worker cache.
     • If found, hydrate into memory and return.

3. Configurable Cache Policy

   • persistPrefetch (default: false).
   • cacheTTL option: expiry time for persistent entries.
   • maxPersistentSize: optional limit for storage size.

4. Offline Support

   • If user is offline, GhostIO can still serve cached data from service worker.

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Example Usage

import { GhostIO } from "ghost-io";

const ghost = new GhostIO({
  persistPrefetch: true,
  cacheTTL: 1000 * 60 * 60, // 1 hour
});

// Prefetch API data
ghost.prefetch("/api/dashboard");

// Later, even after reload:
const data = await ghost.get("/api/dashboard");
console.log(data); // served from service worker cache if available

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Acceptance Criteria

• Prefetched data persists across reloads and browser restarts.
• Expired cache entries are evicted according to TTL.
• Works seamlessly with existing registerAxios integration.
• Fallback to live network fetch if no cache available.

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Tasks

• Add service worker registration + setup.
• Implement persistPrefetch and cacheTTL config options.
• Extend ghost.get(url) to check persistent cache.
• Add eviction policy for expired items.
• Write Jest/e2e tests for persistence + offline scenarios.
• Update README with usage + config examples.

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