sw.js

const cacheName = "cache2"; // Change value to force update
const urls = [
  "./",
  "image/icons/android-chrome-192x192.png", // Favicon, Android Chrome M39+ with 4.0 screen density
  "image/icons/android-chrome-512x512.png", // Favicon, Android Chrome M47+ Splash screen with 4.0 screen density
  "image/icons/apple-touch-icon.png", // Favicon, Apple default
  "browserconfig.xml", // IE11 icon configuration file
  "image/icons/favicon.ico", // Favicon, IE and fallback for other browsers
  "image/icons/favicon-16x16.png", // Favicon, default
  "image/icons/favicon-32x32.png", // Favicon, Safari on Mac OS
  "index.html", // Main HTML file
  "js/main.js", // Main Javascript file
  "manifest.json", // Manifest file
  "image/icons/mstile-150x150.png", // Favicon, Windows 8 / IE11
  "image/icons/safari-pinned-tab.svg", // Favicon, Safari pinned tab
  "css/index.css",
  "js/nfc.js",
  "worker.js",
];

self.addEventListener("install", (event) => {
  // Kick out the old service worker
  self.skipWaiting();

  event.waitUntil(
    caches.open(cacheName).then((cache) => {
      return cache.addAll(urls);
    })
  );
});

self.addEventListener("activate", (event) => {
  // Delete any non-current cache
  event.waitUntil(
    caches.keys().then((keys) => {
      Promise.all(
        keys.map((key) => {
          if (![cacheName].includes(key)) {
            return caches.delete(key);
          }
        })
      );
    })
  );
});

// Offline-first, cache-first strategy
// Kick off two asynchronous requests, one to the cache and one to the network
// If there's a cached version available, use it, but fetch an update for next time.
// Gets data on screen as quickly as possible, then updates once the network has returned the latest data.
self.addEventListener("fetch", (event) => {
  event.respondWith(
    caches.open(cacheName).then(async (cache) => {
      const response = await cache.match(event.request);
      return (
        response ||
        fetch(event.request).then((networkResponse) => {
          cache.put(event.request, networkResponse.clone());
          return networkResponse;
        })
      );
    })
  );
});