https://www.woodviewos.com/service-worker.js

1/*
2Copyright 2015, 2019, 2020, 2021 Google LLC. All Rights Reserved.
3 Licensed under the Apache License, Version 2.0 (the "License");
4 you may not use this file except in compliance with the License.
5 You may obtain a copy of the License at
6 http://www.apache.org/licenses/LICENSE-2.0
7 Unless required by applicable law or agreed to in writing, software
8 distributed under the License is distributed on an "AS IS" BASIS,
9 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
10 See the License for the specific language governing permissions and
11 limitations under the License.
12*/
13
14// Incrementing OFFLINE_VERSION will kick off the install event and force
15// previously cached resources to be updated from the network.
16// This variable is intentionally declared and unused.
17// Add a comment for your linter if you want:
18// eslint-disable-next-line no-unused-vars
19const OFFLINE_VERSION = 1;
20const CACHE_NAME = "offline";
21// Customize this with a different URL if needed.
22const OFFLINE_URL = "offline.html";
23
24self.addEventListener("install", (event) => {
25    event.waitUntil(
26        (async () => {
27            const cache = await caches.open(CACHE_NAME);
28            // Setting {cache: 'reload'} in the new request will ensure that the
29            // response isn't fulfilled from the HTTP cache; i.e., it will be from
30            // the network. 
31            await cache.add(new Request(OFFLINE_URL, { cache: "reload" }));
32        })()
33    );
34    // Force the waiting service worker to become the active service worker.
35    self.skipWaiting();
36});
37
38self.addEventListener("activate", (event) => {
39    event.waitUntil(
40        (async () => {
41            // Enable navigation preload if it's supported.
42            // See https://developers.google.com/web/updates/2017/02/navigation-preload 
43            if ("navigationPreload" in self.registration) {
44                await self.registration.navigationPreload.enable();
45            }
46        })()
47    );
48
49    // Tell the active service worker to take control of the page immediately.
50    self.clients.claim();
51});
52
53self.addEventListener("fetch", (event) => {
54    // We only want to call event.respondWith() if this is a navigation request
55    // for an HTML page.
56    if (event.request.mode === "navigate") {
57        event.respondWith(
58            (async () => {
59                try {
60                    // First, try to use the navigation preload response if it's supported. 
61                    const preloadResponse = await event.preloadResponse;
62                    if (preloadResponse) {
63                        return preloadResponse;
64                    }
65
66                    // Always try the network first.
67                    const networkResponse = await fetch(event.request);
68                    return networkResponse;
69                } catch (error) {
70                    // catch is only triggered if an exception is thrown, which is likely
71                    // due to a network error.
72                    // If fetch() returns a valid HTTP response with a response code in
73                    // the 4xx or 5xx range, the catch() will NOT be called.
74                    console.log("Fetch failed; returning offline page instead.", error);
75
76                    const cache = await caches.open(CACHE_NAME);
77                    const cachedResponse = await cache.match(OFFLINE_URL);
78                    return cachedResponse;
79                }
80            })()
81        );
82    }
83
84    // If our if() condition is false, then this fetch handler won't intercept the
85    // request. If there are any other fetch handlers registered, they will get a
86    // chance to call event.respondWith(). If no fetch handlers call
87    // event.respondWith(), the request will be handled by the browser as if there
88    // were no service worker involvement.
89});