https://ngalamker.com/_service-worker.js

1// Cache name - replace v1 with v2, v3, etc to clear service worker cache on your server
2var CACHE_NAME = 'Cache-Version-v1';
3
4// Files required to make this app work offline
5var REQUIRED_FILES = [
6    'index.php'
7];
8
9self.addEventListener('install', function(event) {
10  // Perform install step:  loading each required file into cache
11  event.waitUntil(
12    caches.open(CACHE_NAME)
13      .then(function(cache) {
14        // Add all offline dependencies to the cache
15        return cache.addAll(REQUIRED_FILES);
16      })
17      .then(function() {
18        return self.skipWaiting();
19      })
20  );
21});
22
23self.addEventListener('fetch', function(event) {
24  event.respondWith(
25    caches.match(event.request)
26      .then(function(response) {
27        // Cache hit - return the response from the cached version
28        if (response) {
29          return response;
30        }
31        // Not in cache - return the result from the live server
32        // `fetch` is essentially a "fallback"
33        return fetch(event.request);
34      }
35    )
36  );
37});
38
39self.addEventListener('activate', function(event) {
40  // Calling claim() to force a "controllerchange" event on navigator.serviceWorker
41  event.waitUntil(self.clients.claim());
42});