feat: service worker

.prettierrc

@@ -1,5 +1,6 @@
 {
-	"useTabs": true,
+	"useTabs": false,
+	"tabWidth": 4,
 	"singleQuote": true,
 	"trailingComma": "none",
 	"printWidth": 100,

src/service-worker.ts

@@ -0,0 +1,76 @@
+/// <reference types="@sveltejs/kit" />
+/// <reference no-default-lib="true"/>
+/// <reference lib="esnext" />
+/// <reference lib="webworker" />
+
+import { build, files, version } from '$service-worker';
+
+// Create a unique cache name for this deployment
+const CACHE = `cache-${version}`;
+
+const ASSETS = [
+    ...build, // the app itself
+    ...files // everything in `static`
+];
+
+const sw = self as unknown as ServiceWorkerGlobalScope;
+
+sw.addEventListener('install', (event) => {
+    // Create a new cache and add all files to it
+    async function addFilesToCache() {
+        const cache = await caches.open(CACHE);
+        await cache.addAll(ASSETS);
+    }
+
+    event.waitUntil(addFilesToCache());
+});
+
+sw.addEventListener('activate', (event) => {
+    // Remove previous cached data from disk
+    async function deleteOldCaches() {
+        for (const key of await caches.keys()) {
+            if (key !== CACHE) await caches.delete(key);
+        }
+    }
+
+    event.waitUntil(deleteOldCaches());
+});
+
+sw.addEventListener('fetch', async (event) => {
+    // ignore POST requests etc
+    if (event.request.method !== 'GET') return;
+
+    const url = new URL(event.request.url);
+    // ignore requests from protocols like chrome-extension
+    if (!url.protocol.startsWith('http')) return;
+
+    async function respond(url: URL): Promise<Response> {
+        const cache = await caches.open(CACHE);
+
+        if (url.protocol)
+            if (ASSETS.includes(url.pathname)) {
+                // `build`/`files` can always be served from the cache
+                return cache.match(url.pathname) as Promise<Response>;
+            }
+
+        // for everything else, try the network first, but
+        // fall back to the cache if we're offline
+        try {
+            const response = await fetch(event.request);
+
+            if (response.status === 200) {
+                cache.put(event.request, response.clone());
+            }
+
+            return response;
+        } catch (error) {
+            const match = await cache.match(event.request);
+
+            if (!match) throw error;
+
+            return match;
+        }
+    }
+
+    event.respondWith(respond(url));
+});