96Implement a simple Service Worker caching strategy

A Service Worker can answer requests from a cache. Implement the three classic strategies as plain functions, so they can be tested outside a worker. Each takes a Request and { cache, fetch }, where cache has the Cache API's match(request) and put(request, response):

• cacheFirst(request, deps): return the cached response if there is one; otherwise fetch, store a clone in the cache if it is OK (response.ok), and return it. Use it for versioned static assets.
• networkFirst(request, { cache, fetch, timeout = 3000 }): try the network; if it fails or takes longer than timeout ms, fall back to the cache; if there is no cached copy either, rethrow the error. Cache successful network responses. Use it for HTML and API reads.
• staleWhileRevalidate(request, { cache, fetch, waitUntil }): return the cached response immediately if there is one and refresh the cache in the background (pass the refresh promise to waitUntil so the worker stays alive); without a cached copy, wait for the network. Use it for avatars and other content that may be slightly old.

Then write pickStrategy(request): navigations (request.mode === "navigate") and /api/ URLs use networkFirst, URLs ending in .js, .css, .woff2 use cacheFirst, images (request.destination === "image") use staleWhileRevalidate, and anything else returns null (let the browser handle it). Non-GET requests always return null.