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  }