# Caching strategies — Web Performance Optimization

Source: https://www.geekswithgeeks.com/en/web-performance/web-perf-06

> Use HTTP caching, service workers, and cache headers to serve content faster on repeat visits.

## HTTP Cache headers

Use `Cache-Control: public, max-age=31536000` for static assets. Set short TTL (e.g., 1 hour) for HTML. Add `ETag` or `Last-Modified` for cache validation. Example: `Cache-Control: max-age=3600, must-revalidate`.

## CDN and edge caching

Store static assets on geographically distributed servers. CDN reduces latency by serving from closest location. Use cache purging to instantly invalidate stale content when deployments happen.

## Client-side caching with Service Workers

Intercept network requests and serve cached versions offline. Use cache strategies: Cache First (for static), Network First (for dynamic), Stale-While-Revalidate (serve stale, update in background).

## Cache invalidation strategies

Use content hashing in filenames (app.a1b2c3d.js) for cache busting. Immediately invalidate on deploy. Monitor cache hit rates (target >90%). Balance between aggressiveness and freshness.

Quick check

**Quiz:** What is a good cache TTL for static assets?

- [ ] 1 year (31536000 seconds)
- [ ] 1 hour
- [ ] No caching