new service worker

src/service-worker.js

@@ -1,82 +1,89 @@
-import { timestamp, files, shell, routes } from '@sapper/service-worker';
+import { timestamp, files, shell } from '@sapper/service-worker'
 
-const ASSETS = `cache${timestamp}`;
+const ASSETS = `cache${timestamp}`
 
 // `shell` is an array of all the files generated by the bundler,
 // `files` is an array of everything in the `static` directory
-const to_cache = shell.concat(files);
-const cached = new Set(to_cache);
+const to_cache = shell.concat(files)
+const staticAssets = new Set(to_cache)
 
-self.addEventListener('install', event => {
-	event.waitUntil(
-		caches
-			.open(ASSETS)
-			.then(cache => cache.addAll(to_cache))
-			.then(() => {
-				self.skipWaiting();
-			})
-	);
-});
+self.addEventListener('install', (event) => {
+  event.waitUntil(
+    caches
+      .open(ASSETS)
+      .then((cache) => cache.addAll(to_cache))
+      .then(() => {
+        self.skipWaiting()
+      })
+  )
+})
 
-self.addEventListener('activate', event => {
-	event.waitUntil(
-		caches.keys().then(async keys => {
-			// delete old caches
-			for (const key of keys) {
-				if (key !== ASSETS) await caches.delete(key);
-			}
+self.addEventListener('activate', (event) => {
+  event.waitUntil(
+    caches.keys().then(async (keys) => {
+      // delete old caches
+      for (const key of keys) {
+        if (key !== ASSETS) await caches.delete(key)
+      }
 
-			self.clients.claim();
-		})
-	);
-});
+      self.clients.claim()
+    })
+  )
+})
 
-self.addEventListener('fetch', event => {
-	if (event.request.method !== 'GET' || event.request.headers.has('range')) return;
+/**
+ * Fetch the asset from the network and store it in the cache.
+ * Fall back to the cache if the user is offline.
+ */
+async function fetchAndCache(request) {
+  const cache = await caches.open(`offline${timestamp}`)
 
-	const url = new URL(event.request.url);
+  try {
+    const response = await fetch(request)
+    cache.put(request, response.clone())
+    return response
+  } catch (err) {
+    const response = await cache.match(request)
+    if (response) return response
 
-	// don't try to handle e.g. data: URIs
-	if (!url.protocol.startsWith('http')) return;
+    throw err
+  }
+}
 
-	// ignore dev server requests
-	if (url.hostname === self.location.hostname && url.port !== self.location.port) return;
+self.addEventListener('fetch', (event) => {
+  if (event.request.method !== 'GET' || event.request.headers.has('range'))
+    return
 
-	// always serve static files and bundler-generated assets from cache
-	if (url.host === self.location.host && cached.has(url.pathname)) {
-		event.respondWith(caches.match(event.request));
-		return;
-	}
+  const url = new URL(event.request.url)
 
-	// for pages, you might want to serve a shell `service-worker-index.html` file,
-	// which Sapper has generated for you. It's not right for every
-	// app, but if it's right for yours then uncomment this section
-	/*
-	if (url.origin === self.origin && routes.find(route => route.pattern.test(url.pathname))) {
-		event.respondWith(caches.match('/service-worker-index.html'));
-		return;
-	}
-	*/
+  // don't try to handle e.g. data: URIs
+  const isHttp = url.protocol.startsWith('http')
+  const isDevServerRequest =
+    url.hostname === self.location.hostname && url.port !== self.location.port
+  const isStaticAsset =
+    url.host === self.location.host && staticAssets.has(url.pathname)
+  const skipBecauseUncached =
+    event.request.cache === 'only-if-cached' && !isStaticAsset
 
-	if (event.request.cache === 'only-if-cached') return;
+  if (isHttp && !isDevServerRequest && !skipBecauseUncached) {
+    event.respondWith(
+      (async () => {
+        // always serve static files and bundler-generated assets from cache.
+        // if your application has other URLs with data that will never change,
+        // set this variable to true for them and they will only be fetched once.
+        const cachedAsset = isStaticAsset && (await caches.match(event.request))
 
-	// for everything else, try the network first, falling back to
-	// cache if the user is offline. (If the pages never change, you
-	// might prefer a cache-first approach to a network-first one.)
-	event.respondWith(
-		caches
-			.open(`offline${timestamp}`)
-			.then(async cache => {
-				try {
-					const response = await fetch(event.request);
-					cache.put(event.request, response.clone());
-					return response;
-				} catch(err) {
-					const response = await cache.match(event.request);
-					if (response) return response;
-
-					throw err;
+        // for pages, you might want to serve a shell `service-worker-index.html` file,
+        // which Sapper has generated for you. It's not right for every
+        // app, but if it's right for yours then uncomment this section
+        /*
+				if (!cachedAsset && url.origin === self.origin && routes.find(route => route.pattern.test(url.pathname))) {
+					return caches.match('/service-worker-index.html');
 				}
-			})
-	);
-});
+				*/
+
+        return cachedAsset || fetchAndCache(event.request)
+      })()
+    )
+  }
+})