Generate a service worker file

// Cache-first: serve from cache, fall back to network.
const CACHE_NAME = "v1";
const PRECACHE = ["/", "/index.html", "/styles.css", "/app.js"];

self.addEventListener("install", (e) => {
  e.waitUntil(caches.open(CACHE_NAME).then((c) => c.addAll(PRECACHE)));
  self.skipWaiting();
});

self.addEventListener("activate", (e) => {
  e.waitUntil(caches.keys().then((keys) =>
    Promise.all(keys.filter((k) => k !== CACHE_NAME).map((k) => caches.delete(k)))
  ));
  self.clients.claim();
});

self.addEventListener("fetch", (e) => {
  e.respondWith(
    caches.match(e.request).then((cached) =>
      cached || fetch(e.request).then((res) => {
        const clone = res.clone();
        caches.open(CACHE_NAME).then((c) => c.put(e.request, clone));
        return res;
      })
    )
  );
});