49 | );
50 | };
51 |
52 | export default Counter;
53 |
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/public/index.html:
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25 | React App
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/src/serviceWorker.js:
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1 | // This optional code is used to register a service worker.
2 | // register() is not called by default.
3 |
4 | // This lets the app load faster on subsequent visits in production, and gives
5 | // it offline capabilities. However, it also means that developers (and users)
6 | // will only see deployed updates on subsequent visits to a page, after all the
7 | // existing tabs open on the page have been closed, since previously cached
8 | // resources are updated in the background.
9 |
10 | // To learn more about the benefits of this model and instructions on how to
11 | // opt-in, read https://bit.ly/CRA-PWA
12 |
13 | const isLocalhost = Boolean(
14 | window.location.hostname === 'localhost' ||
15 | // [::1] is the IPv6 localhost address.
16 | window.location.hostname === '[::1]' ||
17 | // 127.0.0.1/8 is considered localhost for IPv4.
18 | window.location.hostname.match(
19 | /^127(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}$/
20 | )
21 | );
22 |
23 | export function register(config) {
24 | if (process.env.NODE_ENV === 'production' && 'serviceWorker' in navigator) {
25 | // The URL constructor is available in all browsers that support SW.
26 | const publicUrl = new URL(process.env.PUBLIC_URL, window.location.href);
27 | if (publicUrl.origin !== window.location.origin) {
28 | // Our service worker won't work if PUBLIC_URL is on a different origin
29 | // from what our page is served on. This might happen if a CDN is used to
30 | // serve assets; see https://github.com/facebook/create-react-app/issues/2374
31 | return;
32 | }
33 |
34 | window.addEventListener('load', () => {
35 | const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`;
36 |
37 | if (isLocalhost) {
38 | // This is running on localhost. Let's check if a service worker still exists or not.
39 | checkValidServiceWorker(swUrl, config);
40 |
41 | // Add some additional logging to localhost, pointing developers to the
42 | // service worker/PWA documentation.
43 | navigator.serviceWorker.ready.then(() => {
44 | console.log(
45 | 'This web app is being served cache-first by a service ' +
46 | 'worker. To learn more, visit https://bit.ly/CRA-PWA'
47 | );
48 | });
49 | } else {
50 | // Is not localhost. Just register service worker
51 | registerValidSW(swUrl, config);
52 | }
53 | });
54 | }
55 | }
56 |
57 | function registerValidSW(swUrl, config) {
58 | navigator.serviceWorker
59 | .register(swUrl)
60 | .then(registration => {
61 | registration.onupdatefound = () => {
62 | const installingWorker = registration.installing;
63 | if (installingWorker == null) {
64 | return;
65 | }
66 | installingWorker.onstatechange = () => {
67 | if (installingWorker.state === 'installed') {
68 | if (navigator.serviceWorker.controller) {
69 | // At this point, the updated precached content has been fetched,
70 | // but the previous service worker will still serve the older
71 | // content until all client tabs are closed.
72 | console.log(
73 | 'New content is available and will be used when all ' +
74 | 'tabs for this page are closed. See https://bit.ly/CRA-PWA.'
75 | );
76 |
77 | // Execute callback
78 | if (config && config.onUpdate) {
79 | config.onUpdate(registration);
80 | }
81 | } else {
82 | // At this point, everything has been precached.
83 | // It's the perfect time to display a
84 | // "Content is cached for offline use." message.
85 | console.log('Content is cached for offline use.');
86 |
87 | // Execute callback
88 | if (config && config.onSuccess) {
89 | config.onSuccess(registration);
90 | }
91 | }
92 | }
93 | };
94 | };
95 | })
96 | .catch(error => {
97 | console.error('Error during service worker registration:', error);
98 | });
99 | }
100 |
101 | function checkValidServiceWorker(swUrl, config) {
102 | // Check if the service worker can be found. If it can't reload the page.
103 | fetch(swUrl)
104 | .then(response => {
105 | // Ensure service worker exists, and that we really are getting a JS file.
106 | const contentType = response.headers.get('content-type');
107 | if (
108 | response.status === 404 ||
109 | (contentType != null && contentType.indexOf('javascript') === -1)
110 | ) {
111 | // No service worker found. Probably a different app. Reload the page.
112 | navigator.serviceWorker.ready.then(registration => {
113 | registration.unregister().then(() => {
114 | window.location.reload();
115 | });
116 | });
117 | } else {
118 | // Service worker found. Proceed as normal.
119 | registerValidSW(swUrl, config);
120 | }
121 | })
122 | .catch(() => {
123 | console.log(
124 | 'No internet connection found. App is running in offline mode.'
125 | );
126 | });
127 | }
128 |
129 | export function unregister() {
130 | if ('serviceWorker' in navigator) {
131 | navigator.serviceWorker.ready.then(registration => {
132 | registration.unregister();
133 | });
134 | }
135 | }
136 |
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