diff --git a/frontend/src/views/TreeView.tsx b/frontend/src/views/TreeView.tsx
index c0778282..b95f7028 100644
--- a/frontend/src/views/TreeView.tsx
+++ b/frontend/src/views/TreeView.tsx
@@ -183,7 +183,7 @@ function TreeCanvas({ source, tree, src, toast }: {
 
   // Autosave the view document.
   const firstSave = useRef(true)
-  const saveTimer = useRef<number>()
+  const saveTimer = useRef<number | undefined>(undefined)
   const saveNow = useCallback(() => {
     const doc: TreeViewDoc = {
       version: 1,
@@ -228,7 +228,7 @@ function TreeCanvas({ source, tree, src, toast }: {
     el.addEventListener('wheel', onWheel, { passive: false })
     return () => el.removeEventListener('wheel', onWheel)
   }, [])
-  const scrollTimer = useRef<number>()
+  const scrollTimer = useRef<number | undefined>(undefined)
   const onScroll = () => {
     const el = scrollRef.current
     if (!el) return
diff --git a/frontend/vite.config.ts b/frontend/vite.config.ts
index e25db006..8b94649d 100644
--- a/frontend/vite.config.ts
+++ b/frontend/vite.config.ts
@@ -9,9 +9,10 @@ export default defineConfig({
     sourcemap:   false,
     rollupOptions: {
       output: {
-        manualChunks: {
-          plotly: ['plotly.js-dist-min'],
-        },
+        // Vite 8 (rolldown) accepts manualChunks only as a function; the
+        // object form it replaces listed plotly.js-dist-min by package name.
+        manualChunks: (id: string) =>
+          id.includes('plotly.js-dist-min') ? 'plotly' : undefined,
       },
     },
   },