service-worker.js

const staticAssets = [
  './',
  './script.js',
  './style.css',
  './index.html',
  './favourite.html',
  './favourite.js'
];


self.addEventListener('install', (event) => {
  event.waitUntil(
    caches.open('v1')
      .then(res => {
        console.log('wait.........!')
        return res.addAll(staticAssets);
      })
  );
  console.log('installed');
  // var cache = caches.open('v1');
  // cache.addAll(staticAssets);
});

self.addEventListener('activate', (event) => {
  console.log('activated');
});

self.addEventListener('fetch', (ev) => {
  console.log('Fetch from Service Worker ', ev);
  const req = ev.request;
  const url = new URL(req.url);
  if (url.origin === location.origin) {
    ev.respondWith(cacheFirst(req));
  }
  return ev.respondWith(networkFirst(req));
});

async function cacheFirst(req) {
  let cacheRes = await caches.match(req);
  return cacheRes || fetch(req);
}

async function networkFirst(req) {
  const dynamicCache = await caches.open('v1-dynamic');
  try {
    const networkResponse = await fetch(req);
    dynamicCache.put(req, networkResponse.clone());
    return networkResponse;
  } catch (err) {
    const cacheResponse = await caches.match(req);
    return cacheResponse;
  }
}