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        /^127(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[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}/service-worker.js`;
 34  
 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  }