1+ // In production, we register a service worker to serve assets from local cache.
2+
3+ // This lets the app load faster on subsequent visits in production, and gives
4+ // it offline capabilities. However, it also means that developers (and users)
5+ // will only see deployed updates on the "N+1" visit to a page, since previously
6+ // cached resources are updated in the background.
7+
8+ // To learn more about the benefits of this model, read https://goo.gl/KwvDNy.
9+ // This link also includes instructions on opting out of this behavior.
10+
11+ const isLocalhost = Boolean (
12+ window . location . hostname === 'localhost' ||
13+ // [::1] is the IPv6 localhost address.
14+ window . location . hostname === '[::1]' ||
15+ // 127.0.0.1/8 is considered localhost for IPv4.
16+ window . location . hostname . match (
17+ / ^ 1 2 7 (?: \. (?: 2 5 [ 0 - 5 ] | 2 [ 0 - 4 ] [ 0 - 9 ] | [ 0 1 ] ? [ 0 - 9 ] [ 0 - 9 ] ? ) ) { 3 } $ /
18+ )
19+ ) ;
20+
21+ export default function register ( ) {
22+ if ( process . env . NODE_ENV === 'production' && 'serviceWorker' in navigator ) {
23+ // The URL constructor is available in all browsers that support SW.
24+ const publicUrl = new URL ( process . env . PUBLIC_URL , window . location ) ;
25+ if ( publicUrl . origin !== window . location . origin ) {
26+ // Our service worker won't work if PUBLIC_URL is on a different origin
27+ // from what our page is served on. This might happen if a CDN is used to
28+ // serve assets; see https://github.com/facebookincubator/create-react-app/issues/2374
29+ return ;
30+ }
31+
32+ window . addEventListener ( 'load' , ( ) => {
33+ const swUrl = `${ process . env . PUBLIC_URL } ;
34+ console . log ( 'process.env.PUBLIC_URL:' , process . env . PUBLIC_URL , 'swUrl:' , swUrl ) ;
35+ if ( isLocalhost ) {
36+ // This is running on localhost. Lets check if a service worker still exists or not.
37+ checkValidServiceWorker ( swUrl ) ;
38+
39+ // Add some additional logging to localhost, pointing developers to the
40+ // service worker/PWA documentation.
41+ navigator . serviceWorker . ready . then ( ( ) => {
42+ console . log (
43+ 'This web app is being served cache-first by a service ' +
44+ 'worker. To learn more, visit https://goo.gl/SC7cgQ'
45+ ) ;
46+ } ) ;
47+ } else {
48+ // Is not local host. Just register service worker
49+ registerValidSW ( swUrl ) ;
50+ }
51+ } ) ;
52+ }
53+ }
54+
55+ function registerValidSW ( swUrl ) {
56+ navigator . serviceWorker
57+ . register ( swUrl )
58+ . then ( registration => {
59+ registration . onupdatefound = ( ) => {
60+ const installingWorker = registration . installing ;
61+ installingWorker . onstatechange = ( ) => {
62+ if ( installingWorker . state === 'installed' ) {
63+ if ( navigator . serviceWorker . controller ) {
64+ // At this point, the old content will have been purged and
65+ // the fresh content will have been added to the cache.
66+ // It's the perfect time to display a "New content is
67+ // available; please refresh." message in your web app.
68+ console . log ( 'New content is available; please refresh.' ) ;
69+ } else {
70+ // At this point, everything has been precached.
71+ // It's the perfect time to display a
72+ // "Content is cached for offline use." message.
73+ console . log ( 'Content is cached for offline use.' ) ;
74+ }
75+ }
76+ } ;
77+ } ;
78+ } )
79+ . catch ( error => {
80+ console . error ( 'Error during service worker registration:' , error ) ;
81+ } ) ;
82+ }
83+
84+ function checkValidServiceWorker ( swUrl ) {
85+ // Check if the service worker can be found. If it can't reload the page.
86+ fetch ( swUrl )
87+ . then ( response => {
88+ // Ensure service worker exists, and that we really are getting a JS file.
89+ if (
90+ response . status === 404 ||
91+ response . headers . get ( 'content-type' ) . indexOf ( 'javascript' ) === - 1
92+ ) {
93+ // No service worker found. Probably a different app. Reload the page.
94+ navigator . serviceWorker . ready . then ( registration => {
95+ registration . unregister ( ) . then ( ( ) => {
96+ window . location . reload ( ) ;
97+ } ) ;
98+ } ) ;
99+ } else {
100+ // Service worker found. Proceed as normal.
101+ registerValidSW ( swUrl ) ;
102+ }
103+ } )
104+ . catch ( ( ) => {
105+ console . log (
106+ 'No internet connection found. App is running in offline mode.'
107+ ) ;
108+ } ) ;
109+ }
110+
111+ export function unregister ( ) {
112+ if ( 'serviceWorker' in navigator ) {
113+ navigator . serviceWorker . ready . then ( registration => {
114+ registration . unregister ( ) ;
115+ } ) ;
116+ }
117+ }
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