caching in service worker

1 files changed, 79 insertions, 3 deletions

diff --git a/src/service-worker.js b/src/service-worker.js
index fa934333..488b36b4 100644
--- a/src/service-worker.js
+++ b/src/service-worker.js
@@ -1,8 +1,84 @@
+/// <reference types="@sveltejs/kit" />
 import { build, files, version } from "$service-worker";
 
-self.addEventListener("install", (event) => {});
-self.addEventListener("activate", (event) => {});
-self.addEventListener("fetch", (event) => {});
+// Create a unique cache name for this deployment
+const CACHE = `cache-${version}`;
+
+const ASSETS = [
+	...build, // the app itself
+	...files, // everything in `static`
+];
+
+self.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());
+});
+
+self.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());
+});
+
+self.addEventListener("fetch", (event) => {
+	// ignore POST requests etc
+	if (event.request.method !== "GET") return;
+
+	async function respond() {
+		const url = new URL(event.request.url);
+		const cache = await caches.open(CACHE);
+
+		// `build`/`files` can always be served from the cache
+		if (ASSETS.includes(url.pathname)) {
+			const response = await cache.match(url.pathname);
+
+			if (response) {
+				return 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 we're offline, fetch can return a value that is not a Response
+			// instead of throwing - and we can't pass this non-Response to respondWith
+			if (!(response instanceof Response)) {
+				throw new Error("invalid response from fetch");
+			}
+
+			if (response.status === 200) {
+				cache.put(event.request, response.clone());
+			}
+
+			return response;
+		} catch (err) {
+			const response = await cache.match(event.request);
+
+			if (response) {
+				return response;
+			}
+
+			// if there's no cache, then just error out
+			// as there is nothing we can do to respond to this request
+			throw err;
+		}
+	}
+
+	event.respondWith(respond());
+});
+
 self.addEventListener("push", (event) => {
 	const { title, body, url } = event.data.json();
 	const icon = "/images/icon.png";