https://cryptocademy.netlify.app/serviceWorker.js

1// Incrementing OFFLINE_VERSION will kick off the install event and force
2// previously cached resources to be updated from the network.
3const OFFLINE_VERSION = 1.1;
4const CACHE_NAME = 'cryptocademy-offline';
5// Customize this with a different URL if needed.
6const OFFLINE_URL = 'offline.html';
7
8
9
10self.addEventListener('install', (event) => {
11  event.waitUntil((async () => {
12    const cache = await caches.open(CACHE_NAME);
13    // Setting {cache: 'reload'} in the new request will ensure that the response
14    // isn't fulfilled from the HTTP cache; i.e., it will be from the network.
15    await cache.add(new Request(OFFLINE_URL, {cache: 'reload'}));
16  })());
17});
18
19self.addEventListener('activate', (event) => {
20  event.waitUntil((async () => {
21    // Enable navigation preload if it's supported.
22    // See https://developers.google.com/web/updates/2017/02/navigation-preload
23    if ('navigationPreload' in self.registration) {
24      await self.registration.navigationPreload.enable();
25    }
26  })());
27
28  // Tell the active service worker to take control of the page immediately.
29  self.clients.claim();
30});
31
32self.addEventListener('fetch', (event) => {
33  // We only want to call event.respondWith() if this is a navigation request
34  // for an HTML page.
35  if (event.request.mode === 'navigate') {
36    event.respondWith((async () => {
37      try {
38        // First, try to use the navigation preload response if it's supported.
39        const preloadResponse = await event.preloadResponse;
40        if (preloadResponse) {
41          return preloadResponse;
42        }
43
44        const networkResponse = await fetch(event.request);
45        return networkResponse;
46      } 
47      catch (error) {
48        // catch is only triggered if an exception is thrown, which is likely
49        // due to a network error.
50        // If fetch() returns a valid HTTP response with a response code in
51        // the 4xx or 5xx range, the catch() will NOT be called.
52        console.log('Fetch failed; returning offline page instead.', error);
53
54        const cache = await caches.open(CACHE_NAME);
55        const cachedResponse = await cache.match(OFFLINE_URL);
56        
57        return cachedResponse;
58      }
59    })());
60  }
61
62  // If our if() condition is false, then this fetch handler won't intercept the
63  // request. If there are any other fetch handlers registered, they will get a
64  // chance to call event.respondWith(). If no fetch handlers call
65  // event.respondWith(), the request will be handled by the browser as if there
66  // were no service worker involvement.
67});