Which project does this relate to?

Start

Describe the bug

Hot Module Reloading (HMR) does not re-run beforeLoad or loader functions when their code changes.
Even though Vite logs indicate a hot update ([vite] program reload), the functions retain old behavior until a full page refresh.

This causes issues when working on things like localization or dynamic imports that rely on beforeLoad.

Your Example Website or App

create-tanstack base project

Steps to Reproduce the Bug or Issue

1. Create a new project:

   pnpm create @tanstack/start@latest

2. Add this to src/routes/index.tsx:

export const Route = createFileRoute("/")({
  component: App,
  beforeLoad: async () => {
    console.log("hi");
  },
});

3. Run the dev server and edit the console.log message.

Observed behavior:
• The console still prints the old message until a full refresh.
• The Vite terminal logs show:

[vite] (client) hmr update /src/routes/index.tsx
[vite] (ssr) page reload src/routes/index.tsx
[vite] program reload

•	Using the same code in a useEffect does hot reload properly.

Adding this snippet at the bottom of each route fixes the problem:

if (import.meta.hot) {
  import.meta.hot.accept(() => {
    import.meta.hot.invalidate();
  });
}

…but it’s not practical to add to every route file manually.

Expected behavior

HMR should automatically re-run updated beforeLoad and loader code without requiring a full page refresh.

Additional context

💡 Suggested Fix

A simple Vite plugin resolves the issue by invalidating router modules when route files change:

import type { Plugin } from "vite"

export function tanstackRouterHMR(): Plugin {
  return {
    name: "tanstack-router-hmr",
    enforce: "post",
    handleHotUpdate(ctx) {
      const invalidatedModules = []
      for (const mod of ctx.server.moduleGraph.idToModuleMap.values()) {
        if (mod.id?.includes("/router.ts")) {
          invalidatedModules.push(mod)
        }
      }
      return invalidatedModules
    },
  }
}

This ensures route changes propagate correctly through routeTree.gen.ts and router.tsx.

⸻

🧩 Context

Discovered while editing .json message files for i18next — changes to localized messages didn’t reflect until a hard refresh, even though they were dynamically imported inside beforeLoad.