text: // This optional code is used to register a service worker.
  // register() is not called by default.
  
  // 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 subsequent visits to a page, after all the
  // existing tabs open on the page have been closed, since previously cached
  // resources are updated in the background.
  
  // To learn more about the benefits of this model and instructions on how to
  // opt-in, read https://bit.ly/CRA-PWA
  
  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}$/
    )
  );
  
  /**
   * @param {{onUpdate: ?((registration: ServiceWorkerRegistration) => void), onSuccess: ?((registration: ServiceWorkerRegistration) => void)}} [config]
   */
  export function register(config) {
    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.href);
      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/facebook/create-react-app/issues/2374
        return;
      }
  
      window.addEventListener('load', async () => {
        const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`;
  
        if (isLocalhost) {
          // This is running on localhost. Let's check if a service worker still exists or not.
          checkValidServiceWorker(swUrl, config);
  
          // Add some additional logging to localhost, pointing developers to the
          // service worker/PWA documentation.
          await navigator.serviceWorker.ready;
          console.log('This web app is being served cache-first by a service worker. To learn more, visit https://bit.ly/CRA-PWA');
        } else {
          // Is not localhost. Just register service worker
          registerValidSW(swUrl, config);
        }
      });
    }
  }
  
  /**
   * @param {string} swUrl
   * @param {?{onUpdate: ?((registration: ServiceWorkerRegistration) => void), onSuccess: ?((registration: ServiceWorkerRegistration) => void)}} config
   */
  async function registerValidSW(swUrl, config) {
    try {
      const registration = await navigator.serviceWorker.register(swUrl);
      registration.onupdatefound = () => {
        const installingWorker = registration.installing;
        if (installingWorker == null) {
          return;
        }
        installingWorker.onstatechange = () => {
          if (installingWorker.state === 'installed') {
            if (navigator.serviceWorker.controller) {
              // At this point, the updated precached content has been fetched,
              // but the previous service worker will still serve the older
              // content until all client tabs are closed.
              console.log('New content is available and will be used when all tabs for this page are closed. See https://bit.ly/CRA-PWA.');
  
              // Execute callback
              if (config && config.onUpdate) {
                config.onUpdate(registration);
              }
            } 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.');
  
              // Execute callback
              if (config && config.onSuccess) {
                config.onSuccess(registration);
              }
            }
          }
        };
      };
    } catch (error) {
      console.error('Error during service worker registration:', error);
    }
  }
  
  /**
   * @param {string} swUrl
   * @param {?{onUpdate: ?((registration: ServiceWorkerRegistration) => void), onSuccess: ?((registration: ServiceWorkerRegistration) => void)}} config
   */
  async function checkValidServiceWorker(swUrl, config) {
    // Check if the service worker can be found. If it can't reload the page.
    try {
      const response = await fetch(swUrl);
  
      // Ensure service worker exists, and that we really are getting a JS file.
      const contentType = response.headers.get('content-type');
      if (
        response.status === 404 ||
        (contentType != null && contentType.indexOf('javascript') === -1)
      ) {
        // No service worker found. Probably a different app. Reload the page.
        const registration = await navigator.serviceWorker.ready;
        await registration.unregister();
        window.location.reload();
      } else {
        // Service worker found. Proceed as normal.
        registerValidSW(swUrl, config);
      }
    } catch (error) {
      console.log('No internet connection found. App is running in offline mode.');
    }
  }
  
  export async function unregister() {
    if ('serviceWorker' in navigator) {
      const registration = await navigator.serviceWorker.ready;
      await registration.unregister();
    }
  }
  