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// Incrementing OFFLINE_VERSION will kick off the install event and force
// previously cached resources to be updated from the network.
const OFFLINE_VERSION = 1;
const CACHE_NAME = "offline";
self.addEventListener("install", (event) => {
event.waitUntil(
(async () => {
const cache = await caches.open(CACHE_NAME);
// Setting {cache: 'reload'} in the new request will ensure that the
// response isn't fulfilled from the HTTP cache; i.e., it will be from
// the network.
await cache.add(new Request(OFFLINE_URL, { cache: "reload" }));
})()
);
// Force the waiting service worker to become the active service worker.
self.skipWaiting();
});
self.addEventListener("fetch", (event) => {
// We proxify requests through fetch() only if we are offline because it's slower.
if (navigator.onLine === false && event.request.mode === "navigate") {
event.respondWith(
(async () => {
try {
// Always try the network first.
const networkResponse = await fetch(event.request);
return networkResponse;
} catch (error) {
// catch is only triggered if an exception is thrown, which is likely
// due to a network error.
// If fetch() returns a valid HTTP response with a response code in
// the 4xx or 5xx range, the catch() will NOT be called.
const cache = await caches.open(CACHE_NAME);
const cachedResponse = await cache.match(OFFLINE_URL);
return cachedResponse;
}
})()
);
}
});
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