cachefirst

Cache-first is a caching strategy used in web applications and service workers in which a response to a request is served from a local cache if available, with a network fetch used only when the cached entry is missing or invalid. In typical implementations, a service worker opens a named cache, attempts to match the incoming request, and returns the cached response when found. If no cached entry exists, the request is fetched from the network, the response is returned to the page, and a clone of the response is stored in the cache for future use.

This approach offers fast response times and reduced network usage, making it well suited for static assets such as images, stylesheets, JavaScript libraries, and other resources that do not change frequently. It also supports offline access for cached content, which can improve user experience in unreliable network conditions.

However, cache-first can lead to stale content if resources on the server are updated but the cached copies are not promptly refreshed. Cache storage is finite and requires eviction and invalidation policies to prevent unbounded growth. Effective use often involves strategies to refresh data in the background, set expiration, or selectively bypass the cache for dynamic or frequently updated data.

In practice, cache-first is commonly implemented in service workers and can be augmented with libraries such as Workbox, which provide configurable expiration, background updates, and compatibility across browsers. It is one of several caching strategies used to balance performance, freshness, and offline capability in modern web apps.