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@megacarlossm
Forked from JMPerez/service-worker.js
Created September 28, 2020 12:31
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An example of a service worker for serving network first, cache second
// the cache version gets updated every time there is a new deployment
const CACHE_VERSION = 10;
const CURRENT_CACHE = `main-${CACHE_VERSION}`;
// these are the routes we are going to cache for offline support
const cacheFiles = ['/', '/about-me/', '/projects/', '/offline/'];
// on activation we clean up the previously registered service workers
self.addEventListener('activate', evt =>
evt.waitUntil(
caches.keys().then(cacheNames => {
return Promise.all(
cacheNames.map(cacheName => {
if (cacheName !== CURRENT_CACHE) {
return caches.delete(cacheName);
}
})
);
})
)
);
// on install we download the routes we want to cache for offline
self.addEventListener('install', evt =>
evt.waitUntil(
caches.open(CURRENT_CACHE).then(cache => {
return cache.addAll(cacheFiles);
})
)
);
// fetch the resource from the network
const fromNetwork = (request, timeout) =>
new Promise((fulfill, reject) => {
const timeoutId = setTimeout(reject, timeout);
fetch(request).then(response => {
clearTimeout(timeoutId);
fulfill(response);
update(request);
}, reject);
});
// fetch the resource from the browser cache
const fromCache = request =>
caches
.open(CURRENT_CACHE)
.then(cache =>
cache
.match(request)
.then(matching => matching || cache.match('/offline/'))
);
// cache the current page to make it available for offline
const update = request =>
caches
.open(CURRENT_CACHE)
.then(cache =>
fetch(request).then(response => cache.put(request, response))
);
// general strategy when making a request (eg if online try to fetch it
// from the network with a timeout, if something fails serve from cache)
self.addEventListener('fetch', evt => {
evt.respondWith(
fromNetwork(evt.request, 10000).catch(() => fromCache(evt.request))
);
evt.waitUntil(update(evt.request));
});
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