service-worker.js

const APP_VERSION = '1.0.2';
const CACHE_PREFIX = 'clickomania-cache-v';
const CACHE_NAME = `${CACHE_PREFIX}${APP_VERSION}`;
const OFFLINE_ASSETS = [
  './',
  './index.html',
  './favicon.png',
  './manifest.json',
  './service-worker.js',
  './version.json'
];

self.addEventListener('install', event => {
  event.waitUntil(
    caches.open(CACHE_NAME).then(cache => cache.addAll(OFFLINE_ASSETS))
  );
  self.skipWaiting();
});

self.addEventListener('activate', event => {
  event.waitUntil(
    caches.keys().then(keys =>
      Promise.all(
        keys
          .filter(key => key.startsWith(CACHE_PREFIX) && key !== CACHE_NAME)
          .map(key => caches.delete(key))
      )
    )
  );
  self.clients.claim();
});

self.addEventListener('fetch', event => {
  const { request } = event;
  if (request.method !== 'GET') {
    return;
  }

  event.respondWith(
    fetch(request)
      .then(response => {
        const copy = response.clone();
        caches.open(CACHE_NAME).then(cache => cache.put(request, copy));
        return response;
      })
      .catch(() =>
        caches.match(request).then(cachedResponse => {
          if (cachedResponse) {
            return cachedResponse;
          }
          if (request.mode === 'navigate') {
            return caches.match('./index.html');
          }
          return Response.error();
        })
      )
  );
});