Cache First (also known as Cache Falling Back to Network) checks the local cache before making any network request. If the resource is found in cache, it's returned immediately — resulting in near-instant load times. Only when the resource is not cached (a cache miss) does it fetch from the network and then store the response for future use. This strategy is ideal for static assets that rarely change, like fonts, CSS, images, and app shells. Popularized by service worker patterns in Progressive Web Apps (PWAs).

Network First (also called Network Falling Back to Cache) always attempts to fetch fresh data from the network first. If the network request succeeds, it updates the cache with the new response and returns it. If the network fails (e.g., user is offline), it falls back to the cached version. This strategy ensures users always see the most up-to-date content when online, while still providing offline support. It's commonly used for API responses, news feeds, and dynamic content where freshness matters.

Use Cache First when: resources are static and versioned (e.g., /static/logo.v2.png), performance is critical, and stale data is acceptable for a short time. Examples: fonts, CSS, JS bundles, images.

Use Network First when: data freshness is important, the content changes frequently, and you want offline fallback. Examples: API responses, user dashboards, search results, live feeds. The trade-off is slightly slower responses (network latency) in exchange for guaranteed freshness.

With Cache First, a stale cache means users may see outdated content until the cache is cleared or the resource is re-fetched. This is why versioned URLs (e.g., style.v3.css) are recommended.

With Network First, stale cache is less of an issue because the network is checked first. The cached version only serves as a fallback when offline. You can also implement Stale While Revalidate — serve from cache immediately, then update cache in the background — as a hybrid approach balancing speed and freshness.

Absolutely! Modern service worker implementations often use multiple strategies for different resource types. For example: Cache First for static assets (CSS/JS/images), Network First for API calls, and Stale While Revalidate for content that needs both speed and freshness. Tools like Workbox (by Google) make it easy to configure route-based caching strategies in your service worker.

Service workers intercept network requests via the fetch event listener. For Cache First, the worker calls caches.match(request) first; if null, it calls fetch(request) and then cache.put(request, response.clone()). For Network First, it calls fetch(request) first, and only on error does it fall back to caches.match(request). The Cache API (caches.open()) provides the underlying storage mechanism, persisting responses as Request/Response pairs.