text: // 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 pre-cached.
  							// 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();
  		});
  	}
  }
  