static/service-worker.js

const CACHE_NAME = "my-cache-v1";

self.addEventListener("install", (event) => {
  event.waitUntil(
    caches.open(CACHE_NAME).then((cache) => {
      return cache.addAll([
        "/",
        "/static/css/portal.css",
        "/static/js/app.js",
        "/static/images/favicon.png",
      ]);
    })
  );
  self.skipWaiting();
});

self.addEventListener("activate", (event) => {
  const cacheWhitelist = [CACHE_NAME];
  event.waitUntil(
    caches.keys().then((cacheNames) => {
      return Promise.all(
        cacheNames.map((cacheName) => {
          if (!cacheWhitelist.includes(cacheName)) {
            return caches.delete(cacheName);
          }
        })
      );
    })
  );
  self.clients.claim();
});

self.addEventListener("fetch", (event) => {
  event.respondWith(
    caches.match(event.request).then((response) => {
      return response || fetch(event.request);
    })
  );
});