https://homeopgtutor.com/service-worker.js

1/*
2 Copyright 2015 Google Inc. 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'use strict';
15
16// Incrementing CACHE_VERSION will kick off the install event and force previously cached
17// resources to be cached again.
18const CACHE_VERSION = 1;
19let CURRENT_CACHES = {
20  offline: 'offline-v' + CACHE_VERSION
21};
22const OFFLINE_URL = 'offline.html';
23
24function createCacheBustedRequest(url) {
25  let request = new Request(url, {cache: 'reload'});
26  // See https://fetch.spec.whatwg.org/#concept-request-mode
27  // This is not yet supported in Chrome as of M48, so we need to explicitly check to see
28  // if the cache: 'reload' option had any effect.
29  if ('cache' in request) {
30    return request;
31  }
32
33  // If {cache: 'reload'} didn't have any effect, append a cache-busting URL parameter instead.
34  let bustedUrl = new URL(url, self.location.href);
35  bustedUrl.search += (bustedUrl.search ? '&' : '') + 'cachebust=' + Date.now();
36  return new Request(bustedUrl);
37}
38
39self.addEventListener('install', event => {
40  event.waitUntil(
41    // We can't use cache.add() here, since we want OFFLINE_URL to be the cache key, but
42    // the actual URL we end up requesting might include a cache-busting parameter.
43    fetch(createCacheBustedRequest(OFFLINE_URL)).then(function(response) {
44      return caches.open(CURRENT_CACHES.offline).then(function(cache) {
45        return cache.put(OFFLINE_URL, response);
46      });
47    })
48  );
49});
50
51self.addEventListener('activate', event => {
52  // Delete all caches that aren't named in CURRENT_CACHES.
53  // While there is only one cache in this example, the same logic will handle the case where
54  // there are multiple versioned caches.
55  let expectedCacheNames = Object.keys(CURRENT_CACHES).map(function(key) {
56    return CURRENT_CACHES[key];
57  });
58
59  event.waitUntil(
60    caches.keys().then(cacheNames => {
61      return Promise.all(
62        cacheNames.map(cacheName => {
63          if (expectedCacheNames.indexOf(cacheName) === -1) {
64            // If this cache name isn't present in the array of "expected" cache names,
65            // then delete it.
66            console.log('Deleting out of date cache:', cacheName);
67            return caches.delete(cacheName);
68          }
69        })
70      );
71    })
72  );
73});
74
75self.addEventListener('fetch', event => {
76  // We only want to call event.respondWith() if this is a navigation request
77  // for an HTML page.
78  // request.mode of 'navigate' is unfortunately not supported in Chrome
79  // versions older than 49, so we need to include a less precise fallback,
80  // which checks for a GET request with an Accept: text/html header.
81  if (event.request.mode === 'navigate' ||
82      (event.request.method === 'GET' &&
83       event.request.headers.get('accept').includes('text/html'))) {
84    console.log('Handling fetch event for', event.request.url);
85    event.respondWith(
86      fetch(event.request).catch(error => {
87        // The catch is only triggered if fetch() throws an exception, which will most likely
88        // happen due to the server being unreachable.
89        // If fetch() returns a valid HTTP response with an response code in the 4xx or 5xx
90        // range, the catch() will NOT be called. If you need custom handling for 4xx or 5xx
91        // errors, see https://github.com/GoogleChrome/samples/tree/gh-pages/service-worker/fallback-response
92        console.log('Fetch failed; returning offline page instead.', error);
93        return caches.match(OFFLINE_URL);
94      })
95    );
96  }
97
98  // If our if() condition is false, then this fetch handler won't intercept the request.
99  // If there are any other fetch handlers registered, they will get a chance to call
100  // event.respondWith(). If no fetch handlers call event.respondWith(), the request will be
101  // handled by the browser as if there were no service worker involvement.
102});