sw.js

const cacheName = 'my-pwa-cache';
const filesToCache = [
  '/',
  '/index.html',
  '/style.css',
  '/script.js',
  '/game.js',
  '/icon512_maskable.png',
  '/icon512_rounded.png',
];

self.addEventListener('install', function (event) {
  event.waitUntil(
    caches.open(cacheName).then(function (cache) {
      return cache.addAll(filesToCache);
    })
  );
});

self.addEventListener('fetch', function (event) {
  event.respondWith(
    caches.match(event.request).then(function (response) {
      return response || fetch(event.request);
    })
  );
});

let deferredPrompt;

if ('serviceWorker' in navigator) {
  window.addEventListener('beforeinstallprompt', (e) => {
    // Prevent Chrome 67 and earlier from automatically showing the prompt
    e.preventDefault();
    // Stash the event so it can be triggered later.
    deferredPrompt = e;
    // Update UI to notify the user they can add to home screen
    //...
    deferredPrompt.prompt();
  });
}

// Show the prompt
if (deferredPrompt) {
  deferredPrompt.prompt();
  deferredPrompt.userChoice.then((choiceResult) => {
    if (choiceResult.outcome === 'accepted') {
      console.log('User accepted the A2HS prompt');
    } else {
      console.log('User dismissed the A2HS prompt');
    }
    deferredPrompt = null;
  });
}