Readded service worker (pwa)

Author: Fiahblade

src/service-worker.ts

@@ -0,0 +1,80 @@
+//SRC https://dev.to/100lvlmaster/create-a-pwa-with-sveltekit-svelte-a36
+import { build, files, version } from '$service-worker';
+
+const worker = (self as unknown) as ServiceWorkerGlobalScope;
+const FILES = `cache${version}`;
+
+// `build` is an array of all the files generated by the bundler,
+// `files` is an array of everything in the `static` directory
+const to_cache = build.concat(files);
+const staticAssets = new Set(to_cache);
+
+worker.addEventListener('install', (event) => {
+  event.waitUntil(
+    caches
+      .open(FILES)
+      .then((cache) => cache.addAll(to_cache))
+      .then(() => {
+        worker.skipWaiting();
+      })
+  );
+});
+
+worker.addEventListener('activate', (event) => {
+  event.waitUntil(
+    caches.keys().then(async (keys) => {
+      // delete old caches
+      for (const key of keys) {
+        if (key !== FILES) await caches.delete(key);
+      }
+
+      worker.clients.claim();
+    })
+  );
+});
+
+/**
+ * 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: Request) {
+  const cache = await caches.open(`offline${version}`);
+
+  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;
+
+    throw err;
+  }
+}
+
+worker.addEventListener('fetch', (event) => {
+  if (event.request.method !== 'GET' || event.request.headers.has('range')) return;
+
+  const url = new URL(event.request.url);
+
+  // 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 (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));
+
+        return cachedAsset || fetchAndCache(event.request);
+      })()
+    );
+  }
+});
+