Squash Odysseus development history

static/js/panels.js

@@ -0,0 +1,53 @@
+/**
+ * Panel loader registry — imports the modules behind a feature panel the
+ * first time that panel is actually used.
+ *
+ * The panels already populate themselves on open (each fetches its own data).
+ * They were just not *loaded* on demand: every one of them sat on the critical
+ * path of every page load, opened or not.
+ *
+ * A panel only belongs here once it has been checked for import-time side
+ * effects that something outside the panel depends on at startup. Entries get
+ * added one panel at a time, not in bulk.
+ *
+ * Note the service worker still precaches these modules (PANEL_PRECACHE in
+ * sw.js) — they are off the critical path, not off the offline manifest.
+ */
+
+const LOADERS = {
+  editor: () => import('./galleryEditor.js?v=20260909movepicklayer1'),
+};
+
+/**
+ * Build a memoising loader over a name -> import-thunk map. Exported so the
+ * behaviour can be tested without pulling a real panel's module graph in.
+ */
+export function createPanelLoader(loaders) {
+  const cache = new Map();
+  return function load(name) {
+    const cached = cache.get(name);
+    if (cached) return cached;
+    const loader = loaders[name];
+    if (!loader) throw new Error(`loadPanel: unknown panel "${name}"`);
+    // A failed load (offline, 404, syntax error) is not memoised — caching the
+    // rejection would leave the panel broken for the rest of the session even
+    // after the network came back.
+    const pending = Promise.resolve().then(loader).catch((err) => {
+      cache.delete(name);
+      throw err;
+    });
+    cache.set(name, pending);
+    return pending;
+  };
+}
+
+/**
+ * Load a panel's module, once. Returns the same promise on every call for the
+ * same panel; throws for a name that is not registered.
+ */
+export const loadPanel = createPanelLoader(LOADERS);
+
+/** Registered panel names — the registry is the list, not a second copy of it. */
+export function panelNames() {
+  return Object.keys(LOADERS);
+}