React App

February, 2018

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, document.getElementById('root')); 8 | registerServiceWorker(); 9 | -------------------------------------------------------------------------------- /src/registerServiceWorker.js: -------------------------------------------------------------------------------- 1 | // In production, we register a service worker to serve assets from local cache. 2 | 3 | // This lets the app load faster on subsequent visits in production, and gives 4 | // it offline capabilities. However, it also means that developers (and users) 5 | // will only see deployed updates on the "N+1" visit to a page, since previously 6 | // cached resources are updated in the background. 7 | 8 | // To learn more about the benefits of this model, read https://goo.gl/KwvDNy. 9 | // This link also includes instructions on opting out of this behavior. 10 | 11 | const isLocalhost = Boolean( 12 | window.location.hostname === 'localhost' || 13 | // [::1] is the IPv6 localhost address. 14 | window.location.hostname === '[::1]' || 15 | // 127.0.0.1/8 is considered localhost for IPv4. 16 | window.location.hostname.match( 17 | /^127(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}$/ 18 | ) 19 | ); 20 | 21 | export default function register() { 22 | if (process.env.NODE_ENV === 'production' && 'serviceWorker' in navigator) { 23 | // The URL constructor is available in all browsers that support SW. 24 | const publicUrl = new URL(process.env.PUBLIC_URL, window.location); 25 | if (publicUrl.origin !== window.location.origin) { 26 | // Our service worker won't work if PUBLIC_URL is on a different origin 27 | // from what our page is served on. This might happen if a CDN is used to 28 | // serve assets; see https://github.com/facebookincubator/create-react-app/issues/2374 29 | return; 30 | } 31 | 32 | window.addEventListener('load', () => { 33 | const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`; 34 | 35 | if (isLocalhost) { 36 | // This is running on localhost. Lets check if a service worker still exists or not. 37 | checkValidServiceWorker(swUrl); 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://goo.gl/SC7cgQ' 45 | ); 46 | }); 47 | } else { 48 | // Is not local host. Just register service worker 49 | registerValidSW(swUrl); 50 | } 51 | }); 52 | } 53 | } 54 | 55 | function registerValidSW(swUrl) { 56 | navigator.serviceWorker 57 | .register(swUrl) 58 | .then(registration => { 59 | registration.onupdatefound = () => { 60 | const installingWorker = registration.installing; 61 | installingWorker.onstatechange = () => { 62 | if (installingWorker.state === 'installed') { 63 | if (navigator.serviceWorker.controller) { 64 | // At this point, the old content will have been purged and 65 | // the fresh content will have been added to the cache. 66 | // It's the perfect time to display a "New content is 67 | // available; please refresh." message in your web app. 68 | console.log('New content is available; please refresh.'); 69 | } else { 70 | // At this point, everything has been precached. 71 | // It's the perfect time to display a 72 | // "Content is cached for offline use." message. 73 | console.log('Content is cached for offline use.'); 74 | } 75 | } 76 | }; 77 | }; 78 | }) 79 | .catch(error => { 80 | console.error('Error during service worker registration:', error); 81 | }); 82 | } 83 | 84 | function checkValidServiceWorker(swUrl) { 85 | // Check if the service worker can be found. If it can't reload the page. 86 | fetch(swUrl) 87 | .then(response => { 88 | // Ensure service worker exists, and that we really are getting a JS file. 89 | if ( 90 | response.status === 404 || 91 | response.headers.get('content-type').indexOf('javascript') === -1 92 | ) { 93 | // No service worker found. Probably a different app. Reload the page. 94 | navigator.serviceWorker.ready.then(registration => { 95 | registration.unregister().then(() => { 96 | window.location.reload(); 97 | }); 98 | }); 99 | } else { 100 | // Service worker found. Proceed as normal. 101 | registerValidSW(swUrl); 102 | } 103 | }) 104 | .catch(() => { 105 | console.log( 106 | 'No internet connection found. App is running in offline mode.' 107 | ); 108 | }); 109 | } 110 | 111 | export function unregister() { 112 | if ('serviceWorker' in navigator) { 113 | navigator.serviceWorker.ready.then(registration => { 114 | registration.unregister(); 115 | }); 116 | } 117 | } 118 | --------------------------------------------------------------------------------