Frontend caching strategies

import { openDB, DBSchema, IDBPDatabase } from 'idb';

interface CacheEntry {
  data: unknown;
  timestamp: number;
  ttl: number;
  version: string;
}

interface MyDB extends DBSchema {
  cache: {
    key: string;
    value: CacheEntry;
  };
}

export class CacheManager {
  private memoryCache = new Map<string, CacheEntry>();
  private db: IDBPDatabase<MyDB> | null = null;
  private readonly version = 'v1';

  async init() {
    this.db = await openDB<MyDB>('app-cache', 1, {
      upgrade(db) {
        db.createObjectStore('cache');
      },
    });
  }

  private generateKey(url: string, params?: Record<string, unknown>): string {
    const base = `${url}?${JSON.stringify(params ?? {})}`;
    return `${this.version}:${btoa(unescape(encodeURIComponent(base)))}`;
  }

  async get<T>(url: string, params?: Record<string, unknown>): Promise<T | null> {
    const key = this.generateKey(url, params);
    
    // 1. Check memory
    const memEntry = this.memoryCache.get(key);
    if (memEntry && Date.now() - memEntry.timestamp < memEntry.ttl) {
      return memEntry.data as T;
    }

    // 2. Check IndexedDB
    if (!this.db) return null;
    const dbEntry = await this.db.get('cache', key);
    if (dbEntry && Date.now() - dbEntry.timestamp < dbEntry.ttl) {
      this.memoryCache.set(key, dbEntry);
      return dbEntry.data as T;
    }

    return null;
  }

  async set<T>(url: strin

g, data: T, ttl: number = 300_000, params?: Record<string, unknown>) { const key = this.generateKey(url, params); const entry: CacheEntry = { data, timestamp: Date.now(), ttl, version: this.version };

this.memoryCache.set(key, entry);
if (this.db) {
  await this.db.put('cache', entry, key);
}

}

async invalidate(url: string, params?: Record<string, unknown>) { const key = this.generateKey(url, params); this.memoryCache.delete(key); if (this.db) { await this.db.delete('cache', key); } }

async revalidate<T>(url: string, fetcher: () => Promise<T>, params?: Record<string, unknown>, ttl: number = 300_000): Promise<T> { const cached = await this.get<T>(url, params); const fresh = await fetcher(); await this.set(url, fresh, ttl, params); return cached ?? fresh; } }

### Step 3: Integrate with Data Fetching
Wrap your API calls to leverage the cache manager. The pattern returns stale data immediately if available, then fetches fresh data in the background.

```typescript
const cache = new CacheManager();
await cache.init();

export async function fetchWithCache<T>(
  url: string,
  options?: RequestInit,
  ttl?: number
): Promise<T> {
  const cached = await cache.get<T>(url);
  
  // Fire background revalidation
  fetch(url, options)
    .then(res => res.json())
    .then(data => cache.set(url, data, ttl))
    .catch(() => {}); // Silent fail for background updates

  return cached ?? (await fetch(url, options).then(res => res.json()));
}

Step 4: Add Service Worker Interception (Optional but Recommended)

For static assets and repeat API calls, register a service worker that implements network-first with cache fallback.

// sw.js
self.addEventListener('fetch', (event) => {
  if (event.request.url.includes('/api/')) {
    event.respondWith(
      fetch(event.request)
        .then(res => {
          const clone = res.clone();
          caches.open('api-cache').then(c => c.put(event.request, clone));
          return res;
        })
        .catch(() => caches.match(event.request))
    );
  }
});

Architecture Rationale

• Layered storage prevents main-thread blocking while maintaining persistence. Memory cache satisfies synchronous reads; IndexedDB survives navigation and tab closures.
• Key normalization via base64-encoded URL+params prevents collisions across routes, query variations, and authenticated sessions.
• Stale-while-revalidate decouples UI rendering from network latency. Users see instant data; the cache updates silently without blocking interaction.
• TTL + versioning enables safe schema migrations. Changing this.version automatically invalidates all old entries without manual cleanup.

Pitfall Guide

1. Unbounded Cache Growth

Storing responses without eviction policies inevitably triggers quota limits or memory pressure. IndexedDB caps vary by browser (typically 6% of disk or 2GB+), but uncontrolled writes cause QuotaExceededError. Implement LRU eviction or strict TTL decay. Drop entries older than 2x TTL during low-activity windows.

2. Cache Key Collisions

Using raw URLs as keys fails when query order changes, authentication tokens shift, or route parameters mutate. Always normalize keys by sorting parameters, stripping session-specific tokens, and hashing the canonical string. Namespace keys by feature or data domain to isolate invalidation scopes.

3. Synchronous Cache Reads Blocking the Main Thread

localStorage and synchronous IndexedDB polyfills freeze the UI during large reads/writes. Modern IndexedDB is fully asynchronous. Never block render cycles waiting for disk I/O. Preload critical paths into memory cache during app initialization, and use requestIdleCallback for background writes.

4. Ignoring Native HTTP Cache Headers

Bypassing Cache-Control, ETag, and If-None-Match duplicates browser-level caching logic. If your API returns stale-while-revalidate=60, let the browser handle it for static assets. Reserve application-level caching for dynamic, authenticated, or composite endpoints that bypass HTTP caching.

5. Silent Cache Failures Without Graceful Degradation

When IndexedDB fails (private browsing, storage permissions, quota limits), applications crash or hang. Wrap all cache operations in try/catch blocks. Fall back to network fetches transparently. Log cache failures to telemetry, but never block UI rendering on cache availability.

6. Over-Reliance on Service Workers for Dynamic Data

Service workers excel at static asset caching and offline fallbacks, but they lack fine-grained invalidation control. Using SWs for user-specific API responses creates sync nightmares across tabs. Restrict SWs to public, immutable, or semi-static routes. Keep dynamic data caching in the main thread with explicit invalidation hooks.

Best Practices from Production

• Monitor hit/miss ratios: Instrument cache managers to report hit rates, TTL expirations, and invalidation triggers. Aim for >75% hit rates on repeatable queries.
• Version aggressively: Increment cache versions on schema changes, API contract updates, or feature flags. Old caches become liabilities, not assets.
• Isolate invalidation scopes: Invalidate by resource type, not by URL. When a user updates their profile, invalidate all cached profile fragments, not just the exact endpoint.
• Debounce rapid revalidations: Prevent cache thrashing by coalescing identical in-flight requests. Use a pending request map to deduplicate concurrent fetches for the same key.

Production Bundle

Action Checklist

• Initialize layered cache manager on app bootstrap with IndexedDB fallback
• Normalize all cache keys using sorted parameters + version prefix
• Implement stale-while-revalidate pattern for all repeatable API calls
• Set explicit TTL values per data type (static: 3600s, dynamic: 300s, real-time: 0s)
• Add background revalidation with request deduplication and error boundaries
• Instrument cache hit/miss ratios and TTL expirations into telemetry pipeline
• Register service worker for static assets only; exclude authenticated API routes
• Test cache behavior in incognito mode, storage-quota limits, and offline conditions

Decision Matrix

Scenario	Recommended Approach	Why	Cost Impact
Public documentation / marketing site	Service Worker + Cache-First	Assets are immutable; network requests are unnecessary after first load	Reduces CDN egress by 60-80%
User dashboard with frequent updates	In-Memory + IndexedDB + Stale-While-Revalidate	Balances instant UI with background freshness; avoids blocking renders	Increases storage overhead by ~15MB/session
Real-time chat / live metrics	No Client Cache + WebSocket/SSE	Caching introduces unacceptable staleness; push updates are required	Higher bandwidth usage, lower latency
E-commerce product catalog	HTTP Cache Headers + IndexedDB LRU	Product data changes infrequently; native caching handles CDN edge efficiently	Minimal implementation cost, high cache hit rate

Configuration Template

// cache.config.ts
export const CACHE_CONFIG = {
  version: '2024.06',
  ttl: {
    static: 3600_000,
    dynamic: 300_000,
    realTime: 0,
    auth: 1800_000,
  },
  eviction: {
    strategy: 'LRU',
    maxSize: 500,
    cleanupInterval: 60_000,
  },
  fallback: {
    networkOnQuotaExceeded: true,
    silentFailOnError: true,
  },
};

// Initialize
import { CacheManager } from './CacheManager';
export const cache = new CacheManager();
cache.init().catch(console.warn);

Quick Start Guide

1. Install idb (npm i idb) and create CacheManager.ts with the provided implementation.
2. Replace direct fetch() calls with fetchWithCache() or your data library's queryClient.fetchQuery wrapper, passing explicit TTL values.
3. Add cache invalidation hooks to mutation endpoints (e.g., cache.invalidate('/api/user/profile') after POST/PUT).
4. Register sw.js in your build pipeline using vite-plugin-pwa or workbox-webpack-plugin, restricting it to static asset routes.
5. Run Lighthouse and check the "Cache" audit; verify hit rates in your telemetry dashboard within 24 hours of deployment.