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+// In production, we register a service worker to serve assets from local cache.
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+
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+// This lets the app load faster on subsequent visits in production, and gives
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+// it offline capabilities. However, it also means that developers (and users)
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+// will only see deployed updates on the "N+1" visit to a page, since previously
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+// cached resources are updated in the background.
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+
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+// To learn more about the benefits of this model, read https://goo.gl/KwvDNy.
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+// This link also includes instructions on opting out of this behavior.
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+
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+const isLocalhost = Boolean(
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+ window.location.hostname === 'localhost' ||
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+ // [::1] is the IPv6 localhost address.
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+ window.location.hostname === '[::1]' ||
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+ // 127.0.0.1/8 is considered localhost for IPv4.
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+ window.location.hostname.match(
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+ /^127(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}$/
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+ )
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+);
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+
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+export default function register() {
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+ if (process.env.NODE_ENV === 'production' && 'serviceWorker' in navigator) {
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+ // The URL constructor is available in all browsers that support SW.
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+ const publicUrl = new URL(process.env.PUBLIC_URL, window.location);
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+ if (publicUrl.origin !== window.location.origin) {
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+ // Our service worker won't work if PUBLIC_URL is on a different origin
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+ // from what our page is served on. This might happen if a CDN is used to
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+ // serve assets; see https://github.com/facebookincubator/create-react-app/issues/2374
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+ return;
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+ }
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+
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+ window.addEventListener('load', () => {
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+ const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`;
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+
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+ if (isLocalhost) {
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+ // This is running on localhost. Lets check if a service worker still exists or not.
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+ checkValidServiceWorker(swUrl);
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+
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+ // Add some additional logging to localhost, pointing developers to the
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+ // service worker/PWA documentation.
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+ navigator.serviceWorker.ready.then(() => {
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+ console.log(
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+ 'This web app is being served cache-first by a service ' +
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+ 'worker. To learn more, visit https://goo.gl/SC7cgQ'
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+ );
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+ });
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+ } else {
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+ // Is not local host. Just register service worker
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+ registerValidSW(swUrl);
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+ }
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+ });
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+ }
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+}
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+
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+function registerValidSW(swUrl) {
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+ navigator.serviceWorker
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+ .register(swUrl)
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+ .then(registration => {
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+ registration.onupdatefound = () => {
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+ const installingWorker = registration.installing;
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+ installingWorker.onstatechange = () => {
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+ if (installingWorker.state === 'installed') {
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+ if (navigator.serviceWorker.controller) {
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+ // At this point, the old content will have been purged and
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+ // the fresh content will have been added to the cache.
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+ // It's the perfect time to display a "New content is
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+ // available; please refresh." message in your web app.
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+ console.log('New content is available; please refresh.');
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+ } else {
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+ // At this point, everything has been precached.
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+ // It's the perfect time to display a
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+ // "Content is cached for offline use." message.
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+ console.log('Content is cached for offline use.');
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+ }
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+ }
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+ };
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+ };
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+ })
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+ .catch(error => {
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+ console.error('Error during service worker registration:', error);
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+ });
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+}
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+
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+function checkValidServiceWorker(swUrl) {
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+ // Check if the service worker can be found. If it can't reload the page.
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+ fetch(swUrl)
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+ .then(response => {
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+ // Ensure service worker exists, and that we really are getting a JS file.
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+ if (
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+ response.status === 404 ||
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+ response.headers.get('content-type').indexOf('javascript') === -1
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+ ) {
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+ // No service worker found. Probably a different app. Reload the page.
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+ navigator.serviceWorker.ready.then(registration => {
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+ registration.unregister().then(() => {
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+ window.location.reload();
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+ });
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+ });
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+ } else {
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+ // Service worker found. Proceed as normal.
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+ registerValidSW(swUrl);
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+ }
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+ })
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+ .catch(() => {
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+ console.log(
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+ 'No internet connection found. App is running in offline mode.'
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+ );
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+ });
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+}
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+
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+export function unregister() {
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+ if ('serviceWorker' in navigator) {
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+ navigator.serviceWorker.ready.then(registration => {
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+ registration.unregister();
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+ });
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+ }
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+}
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