add service worker for offline access

main.js

@@ -99,6 +99,19 @@ function endOfComputation() {
 	switchInputs(true);
 }
 
+if ("serviceWorker" in navigator) {
+  navigator.serviceWorker.register("workers/service.js").then(
+    (registration) => {
+      console.log("Service worker registration successful:", registration);
+    },
+    (error) => {
+      console.error(`Service worker registration failed: ${error}`);
+    },
+  );
+} else {
+  console.error("Service workers are not supported.");
+}
+
 const expr = document.querySelector("#expr");
 let selectionStart = 0;
 let selectionEnd = 0;

workers/service.js

@@ -0,0 +1,60 @@
+/*
+Copyright (C) 2025 filifa
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+const VERSION = "v1";
+
+const CACHE_NAME = `mcalc-${VERSION}`;
+
+const APP_STATIC_RESOURCES = [
+	"../index.html",
+	"../legal.html",
+	"../styles.css",
+	"../main.js",
+	"evaluate.js",
+	"lexer.js",
+	"math.js",
+	"parser.js",
+	"../icon.svg"
+];
+
+// On install, cache the static resources
+self.addEventListener("install", (event) => {
+  event.waitUntil(
+    (async () => {
+      const cache = await caches.open(CACHE_NAME);
+      cache.addAll(APP_STATIC_RESOURCES);
+    })(),
+  );
+});
+
+// delete old caches on activate
+self.addEventListener("activate", (event) => {
+  event.waitUntil(
+    (async () => {
+      const names = await caches.keys();
+      await Promise.all(
+        names.map((name) => {
+          if (name !== CACHE_NAME) {
+            return caches.delete(name);
+          }
+          return undefined;
+        }),
+      );
+      await clients.claim();
+    })(),
+  );
+});