inkwell/frontend/public/sw.js

// Inkwell service worker: makes the web app installable and shows a page when a
// navigation has no network. Deliberately not offline-first (the desktop and Android
// apps are): it caches only the offline page, so an installed copy is always the live
// web app.
const CACHE = "inkwell-shell-v1";
const OFFLINE_URL = "/offline.html";

self.addEventListener("install", (event) => {
  event.waitUntil(
    caches
      .open(CACHE)
      .then((cache) => cache.add(OFFLINE_URL))
      .then(() => self.skipWaiting()),
  );
});

self.addEventListener("activate", (event) => {
  event.waitUntil(
    caches
      .keys()
      .then((keys) => Promise.all(keys.filter((k) => k !== CACHE).map((k) => caches.delete(k))))
      .then(() => self.clients.claim()),
  );
});

// Only intercept page navigations: try the network, fall back to the cached
// offline page when the server is unreachable. All other requests (hashed
// assets, /api/*) are left untouched and hit the network normally.
self.addEventListener("fetch", (event) => {
  if (event.request.mode !== "navigate") return;
  event.respondWith(fetch(event.request).catch(() => caches.match(OFFLINE_URL)));
});