https://www.imperial-properties.com/serviceWorker.js

1const _cacheName = "offline";
2
3const _cacheItems = [
4    "/favicon.ico",
5    "/static/offline.html"
6];
7
8self.addEventListener("install", function (event) {
9    event.waitUntil(
10        caches.open(_cacheName)
11            .then(function (cache) {
12                return cache.addAll(_cacheItems);
13            })
14    );
15});
16
17self.addEventListener("fetch", function (event) {
18    event.respondWith(
19        caches.match(event.request).then(function (response) {
20            return response || fetch(event.request);
21        }).catch(function () {
22            return caches.match("/static/offline.html");
23        })
24    );
25});
26
27self.addEventListener("activate", function (event) {
28    const cacheAllowlist = [_cacheName];
29    event.waitUntil(
30        caches.keys().then(function (cacheNames) {
31            return Promise.all(
32                cacheNames.map(function (cacheName) {
33                    if (cacheAllowlist.indexOf(cacheName) === -1) {
34                        return caches.delete(cacheName);
35                    }
36                })
37            );
38        })
39    );
40});