Service Worker

if ("serviceWorker" in navigator) {
  window.addEventListener("load", async () => {
    try {
      const reg = await navigator.serviceWorker.register("/sw.js");
      console.log("SW registered:", reg.scope);
    } catch (err) {
      console.error("SW failed:", err);
    }
  });
}

// sw.js example
self.addEventListener("install", e => self.skipWaiting());
self.addEventListener("fetch", e => {
  e.respondWith(caches.match(e.request).then(r => r || fetch(e.request)));
});