https://www.savira.cz/sw.js

1const offlineUrl = '/offline';
2
3self.addEventListener('install', function(event) {
4    let offlineRequest = new Request(offlineUrl);
5    event.waitUntil(
6        fetch(offlineRequest).then(function(response) {
7            return caches.open('offline').then(function(cache) {
8                console.log('[oninstall] Cached offline page', response.url);
9                return cache.put(offlineRequest, response);
10            });
11        })
12    );
13});
14
15self.addEventListener('fetch', function(event) {
16    let request = event.request;
17
18    if (request.url.match(/\.(css|jpg|jpeg|png|gif|js|woff|woff2|ttf|svg|mp4|webp)$/) || request.url.indexOf(request.referrer) !== 0) {
19        return;
20    } else if (request.method === 'GET') {
21        event.respondWith(
22            fetch(request).catch(function(error) {
23                console.log(
24                    '[onfetch] Failed. Serving cached offline fallback ' +
25                    error
26                );
27                return caches.open('offline').then(function(cache) {
28                    return cache.match(offlineUrl);
29                });
30            })
31        );
32    }
33});