SW

1 files changed, 82 insertions, 0 deletions

diff --git a/service-worker.js b/service-worker.js
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index 0000000..aaac385
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+++ b/service-worker.js
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+/*
+Copyright 2015, 2019 Google Inc. All Rights Reserved.
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+ You may obtain a copy of the License at
+ http://www.apache.org/licenses/LICENSE-2.0
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+*/
+
+// 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';
+
+const STATIC_URLS = [ 
+  "/",
+  "/index.html",
+  "/manifest.webmanifest",
+  "/icon-192x192.png",
+  "/icon-256x256.png",
+  "/icon-384x384.png",
+  "/icon-512x512.png"
+]; 
+
+self.addEventListener('install', (event) => {
+  event.waitUntil((async () => {
+    const cache = await caches.open(CACHE_NAME);
+    await cache.addAll(STATIC_URLS);
+  })());
+});
+
+self.addEventListener('activate', (event) => {
+  event.waitUntil((async () => {
+    // Enable navigation preload if it's supported.
+    // See https://developers.google.com/web/updates/2017/02/navigation-preload
+    if ('navigationPreload' in self.registration) {
+      await self.registration.navigationPreload.enable();
+    }
+  })());
+
+  // Tell the active service worker to take control of the page immediately.
+  self.clients.claim();
+});
+
+self.addEventListener('fetch', (event) => {
+  // We only want to call event.respondWith() if this is a navigation request
+  // for an HTML page.
+  if (event.request.mode === 'navigate') {
+    event.respondWith((async () => {
+      try {
+        // First, try to use the navigation preload response if it's supported.
+        const preloadResponse = await event.preloadResponse;
+        if (preloadResponse) {
+          return preloadResponse;
+        }
+
+        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.
+        console.log('Fetch failed; returning offline page instead.', error);
+
+        const cache = await caches.open(CACHE_NAME);
+        const cachedResponse = await cache.match(OFFLINE_URL);
+        return cachedResponse;
+      }
+    })());
+  }
+
+  // If our if() condition is false, then this fetch handler won't intercept the
+  // request. If there are any other fetch handlers registered, they will get a
+  // chance to call event.respondWith(). If no fetch handlers call
+  // event.respondWith(), the request will be handled by the browser as if there
+  // were no service worker involvement.
+});
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