89 lines
3.3 KiB
JavaScript
89 lines
3.3 KiB
JavaScript
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/*
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Copyright 2015, 2019, 2020 Google LLC. All Rights Reserved.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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const CACHE_NAME = 'offline';
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// Customize this with a different URL if needed.
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const OFFLINE_URL = 'static/offline.html';
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self.addEventListener('install', event => {
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event.waitUntil(
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(async () => {
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const cache = await caches.open(CACHE_NAME);
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// Setting {cache: 'reload'} in the new request will ensure that the
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// response isn't fulfilled from the HTTP cache; i.e., it will be from
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// the network.
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await cache.add(new Request(OFFLINE_URL, { cache: 'reload' }));
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})()
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);
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// Force the waiting service worker to become the active service worker.
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self.skipWaiting();
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});
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self.addEventListener('activate', event => {
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event.waitUntil(
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(async () => {
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// Enable navigation preload if it's supported.
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// See https://developers.google.com/web/updates/2017/02/navigation-preload
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if ('navigationPreload' in self.registration) {
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await self.registration.navigationPreload.enable();
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}
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})()
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);
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// Tell the active service worker to take control of the page immediately.
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self.clients.claim();
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});
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self.addEventListener('fetch', event => {
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// We only want to call event.respondWith() if this is a navigation request
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// for an HTML page.
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if (event.request.mode === 'navigate') {
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event.respondWith((async () => {
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try {
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// First, try to use the navigation preload response if it's supported.
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const preloadResponse = await event.preloadResponse;
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if (preloadResponse) {
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return preloadResponse;
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}
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// Always try the network first.
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const networkResponse = await fetch(event.request);
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return networkResponse;
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} catch (error) {
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// catch is only triggered if an exception is thrown, which is likely
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// due to a network error.
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// If fetch() returns a valid HTTP response with a response code in
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// the 4xx or 5xx range, the catch() will NOT be called.
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console.log('Fetch failed; returning offline page instead.', error);
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const cache = await caches.open(CACHE_NAME);
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const cachedResponse = await cache.match(OFFLINE_URL);
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return cachedResponse;
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}
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})());
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}
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// If our if() condition is false, then this fetch handler won't intercept the
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// request. If there are any other fetch handlers registered, they will get a
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// chance to call event.respondWith(). If no fetch handlers call
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// event.respondWith(), the request will be handled by the browser as if there
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// were no service worker involvement.
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});
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