# All files / src/lib registerServiceWorker.js

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     // In production, we register a service worker to serve assets from local cache.

    // This lets the app load faster on subsequent visits in production, and gives
    // it offline capabilities. However, it also means that developers (and users)
    // will only see deployed updates on the "N+1" visit to a page, since previously
    // cached resources are updated in the background.

    // To learn more about the benefits of this model, read https://goo.gl/KwvDNy.
    // This link also includes instructions on opting out of this behavior.

    const isLocalhost = Boolean(
      window.location.hostname === "localhost" ||
        // [::1] is the IPv6 localhost address.
        window.location.hostname === "[::1]" ||
        // 127.0.0.1/8 is considered localhost for IPv4.
        window.location.hostname.match(/^127(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}$/)
    );

    export default function register() {
      if (process.env.NODE_ENV === "production" && "serviceWorker" in navigator) {
        // The URL constructor is available in all browsers that support SW.
        const publicUrl = new URL(process.env.PUBLIC_URL, window.location);
        if (publicUrl.origin !== window.location.origin) {
          // Our service worker won't work if PUBLIC_URL is on a different origin
          // from what our page is served on. This might happen if a CDN is used to
          // serve assets; see https://github.com/facebookincubator/create-react-app/issues/2374
          return;
        }

        window.addEventListener("load", () => {
          const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`;

          if (isLocalhost) {
            // This is running on localhost. Lets check if a service worker still exists or not.
            checkValidServiceWorker(swUrl);

            // Add some additional logging to localhost, pointing developers to the
            // service worker/PWA documentation.
            navigator.serviceWorker.ready.then(() => {
              console.log(
                "This web app is being served cache-first by a service " +
                  "worker. To learn more, visit https://goo.gl/SC7cgQ"
              );
            });
          } else {
            // Is not local host. Just register service worker
            registerValidSW(swUrl);
          }
        });
      }
    }

    function registerValidSW(swUrl) {
      navigator.serviceWorker
        .register(swUrl)
        .then(registration => {
          registration.onupdatefound = () => {
            const installingWorker = registration.installing;
            installingWorker.onstatechange = () => {
              if (installingWorker.state === "installed") {
                if (navigator.serviceWorker.controller) {
                  // At this point, the old content will have been purged and
                  // the fresh content will have been added to the cache.
                  // It's the perfect time to display a "New content is
                  // available; please refresh." message in your web app.
                  console.log("New content is available; please refresh.");
                } else {
                  // At this point, everything has been precached.
                  // It's the perfect time to display a
                  // "Content is cached for offline use." message.
                  console.log("Content is cached for offline use.");
                }
              }
            };
          };
        })
        .catch(error => {
          console.error("Error during service worker registration:", error);
        });
    }

    function checkValidServiceWorker(swUrl) {
      // Check if the service worker can be found. If it can't reload the page.
      fetch(swUrl)
        .then(response => {
          // Ensure service worker exists, and that we really are getting a JS file.
          if (
            response.status === 404 ||
            response.headers.get("content-type").indexOf("javascript") === -1
          ) {
            // No service worker found. Probably a different app. Reload the page.
            navigator.serviceWorker.ready.then(registration => {
              registration.unregister().then(() => {
                window.location.reload();
              });
            });
          } else {
            // Service worker found. Proceed as normal.
            registerValidSW(swUrl);
          }
        })
        .catch(() => {
          console.log("No internet connection found. App is running in offline mode.");
        });
    }

    export function unregister() {
      if ("serviceWorker" in navigator) {
        navigator.serviceWorker.ready.then(registration => {
          registration.unregister();
        });
      }
    }