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// In production, we register a service worker to serve assets from local cache. |
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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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// 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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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}$/ |
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) |
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); |
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export default function register() { |
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if (process.env.NODE_ENV === 'production' && 'serviceWorker' in navigator) { |
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// The URL constructor is available in all browsers that support SW. |
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const publicUrl = new URL(process.env.PUBLIC_URL, window.location); |
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if (publicUrl.origin !== window.location.origin) { |
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// Our service worker won't work if PUBLIC_URL is on a different origin |
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// from what our page is served on. This might happen if a CDN is used to |
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// serve assets; see https://github.com/facebookincubator/create-react-app/issues/2374 |
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return; |
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} |
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window.addEventListener('load', () => { |
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const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`; |
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if (!isLocalhost) { |
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// Is not local host. Just register service worker |
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registerValidSW(swUrl); |
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} else { |
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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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}); |
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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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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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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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kukiron /
MetaDraft
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This checks looks for references to variables that have not been declared. This is most likey a typographical error or a variable has been renamed.
To learn more about declaring variables in Javascript, see the MDN.