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(/^127(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}$/)
 19  );
 20  
 21  export function register(config) {
 22    if (process.env.NODE_ENV === "production" && "serviceWorker" in navigator) {
 23      // The URL constructor is available in all browsers that support SW.
 24      const publicUrl = new URL(process.env.PUBLIC_URL, window.location.href);
 25      if (publicUrl.origin !== window.location.origin) {
 26        // Our service worker won't work if PUBLIC_URL is on a different origin
 27        // from what our page is served on. This might happen if a CDN is used to
 28        // serve assets; see https://github.com/facebook/create-react-app/issues/2374
 29        return;
 30      }
 31  
 32      window.addEventListener("load", () => {
 33        const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`;
 34  
 35        if (isLocalhost) {
 36          // This is running on localhost. Let's check if a service worker still exists or not.
 37          checkValidServiceWorker(swUrl, config);
 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://bit.ly/CRA-PWA"
 45            );
 46          });
 47        } else {
 48          // Is not localhost. Just register service worker
 49          registerValidSW(swUrl, config);
 50        }
 51      });
 52    }
 53  }
 54  
 55  function registerValidSW(swUrl, config) {
 56    navigator.serviceWorker
 57      .register(swUrl)
 58      .then((registration) => {
 59        registration.onupdatefound = () => {
 60          const installingWorker = registration.installing;
 61          if (installingWorker == null) {
 62            return;
 63          }
 64          installingWorker.onstatechange = () => {
 65            if (installingWorker.state === "installed") {
 66              if (navigator.serviceWorker.controller) {
 67                // At this point, the updated precached content has been fetched,
 68                // but the previous service worker will still serve the older
 69                // content until all client tabs are closed.
 70                console.log(
 71                  "New content is available and will be used when all " +
 72                    "tabs for this page are closed. See https://bit.ly/CRA-PWA."
 73                );
 74  
 75                // Execute callback
 76                if (config && config.onUpdate) {
 77                  config.onUpdate(registration);
 78                }
 79              } else {
 80                // At this point, everything has been precached.
 81                // It's the perfect time to display a
 82                // "Content is cached for offline use." message.
 83                console.log("Content is cached for offline use.");
 84  
 85                // Execute callback
 86                if (config && config.onSuccess) {
 87                  config.onSuccess(registration);
 88                }
 89              }
 90            }
 91          };
 92        };
 93      })
 94      .catch((error) => {
 95        console.error("Error during service worker registration:", error);
 96      });
 97  }
 98  
 99  function checkValidServiceWorker(swUrl, config) {
100    // Check if the service worker can be found. If it can't reload the page.
101    fetch(swUrl)
102      .then((response) => {
103        // Ensure service worker exists, and that we really are getting a JS file.
104        const contentType = response.headers.get("content-type");
105        if (
106          response.status === 404 ||
107          (contentType != null && contentType.indexOf("javascript") === -1)
108        ) {
109          // No service worker found. Probably a different app. Reload the page.
110          navigator.serviceWorker.ready.then((registration) => {
111            registration.unregister().then(() => {
112              window.location.reload();
113            });
114          });
115        } else {
116          // Service worker found. Proceed as normal.
117          registerValidSW(swUrl, config);
118        }
119      })
120      .catch(() => {
121        console.log("No internet connection found. App is running in offline mode.");
122      });
123  }
124  
125  export function unregister() {
126    if ("serviceWorker" in navigator) {
127      navigator.serviceWorker.ready.then((registration) => {
128        registration.unregister();
129      });
130    }
131  }