createMiddleware is not a function on cold-start SSR in vite dev (not HMR; @tanstack/react-start@1.168.9, Vite 7.3.3)

[devnomic]

Summary

@tanstack/react-start@1.168.9 throws (0, __vite_ssr_import_N__.createMiddleware) is not a function on the first SSR request after vite dev boots. No HMR involved — error fires on cold start, before any file edit.

Distinct from #7285 (which fails on HMR re-evaluation only, with cold start succeeding). Same root mechanism (Vite SSR module runner mishandling export * re-exports through TanStack's package facade), different surfacing.

npm run build + npm run start (prod SSR via Rollup) work correctly — Rollup statically resolves the export * chain, so the bug only surfaces in vite dev's on-demand SSR module evaluation.

Versions

• @tanstack/react-start: ^1.168.9
• @tanstack/react-router: ^1.170.6
• @tanstack/router-plugin: ^1.168.9
• vite: ^7.3.3
• nitro: ^3.0.260429-beta
• Node: v24.5.0
• OS: macOS (darwin 25.3.0)

Reproduction

Minimal user code triggering the bug:

// src/middlewares/auth.ts
import { createMiddleware } from "@tanstack/react-start"

export const ensureAuthenticatedMiddleware = createMiddleware().server(async ({ next }) => {
  return next({ context: {} })
})

Any file in that imports this middleware will trigger the error on first SSR request.

Stack trace

TypeError: (0 , __vite_ssr_import_2__.createMiddleware) is not a function
    at /<repo>/src/middlewares/auth.ts:8:46
    at ESModulesEvaluator.runInlinedModule (file:///<repo>/node_modules/vite/dist/node/module-runner.js:913:3)
    at ModuleRunner.directRequest (file:///<repo>/node_modules/vite/dist/node/module-runner.js:1146:59)
    at ModuleRunner.cachedRequest (file:///<repo>/node_modules/vite/dist/node/module-runner.js:1053:73)
    at /<repo>/src/routes/_authenticated/-serverfns/auth.ts:1:1
    ...

Diagnosis

createMiddleware is not a direct export of @tanstack/react-start anymore — it's re-exported transitively:

// @tanstack/react-start/dist/esm/index.js
import { useServerFn } from "./useServerFn.js";
import { createServerFn } from "@tanstack/start-client-core";
import { Hydrate } from "@tanstack/react-start-client";
export * from "@tanstack/start-client-core";  // ← createMiddleware lives here
export { Hydrate, createServerFn, useServerFn };

Plain Node ESM resolves the chain correctly:

\$ node -e "import('@tanstack/react-start').then(m => console.log(typeof m.createMiddleware))"
function

But Vite's SSR ESModulesEvaluator returns undefined for .createMiddleware on the namespace it loaded for @tanstack/react-start. The export * re-export from @tanstack/start-client-core is not being walked through to the user module.

Workaround (confirmed working)

Adding both packages to ssr.optimizeDeps.include flattens the re-export chain at optimize time (mirroring Rollup's behavior in prod):

// vite.config.ts
export default defineConfig({
  plugins: [/* ... */],
  ssr: {
    optimizeDeps: {
      include: ["@tanstack/react-start", "@tanstack/start-client-core"],
    },
  },
})

Cold start succeeds with this in place; full reinstall + cache clear without it does not help.

What I've ruled out

• ✅ Fresh rm -rf node_modules && npm install
• ✅ Cleared node_modules/.vite, .vite, .nitro, .output
• ✅ Bumped Vite 7.3.2 → 7.3.3
• ✅ Verified node -e \"import('@tanstack/react-start')\" exports createMiddleware
• ✅ Verified dist/esm/index.js contains the export * re-export at runtime
• ❌ Importing directly from @tanstack/start-client-core bypasses the issue but breaks the client bundle (leaks node:async_hooks into browser code — the react-start facade is intentionally protecting against this via export conditions)

Related

• SSR HMR: createStartHandler is not a function on every re-evaluation (re-occurrence of #5673, 1.167.50) #7285 — same root cause, HMR re-evaluation surface (closed as "fix in Vite 8" but reporters confirm bug persists on Vite 8)
• ReferenceError: Cannot access '__vite_ssr_import_2__' before initialization #5673 — original report against Nitro
• Vite PR linked in SSR HMR: createStartHandler is not a function on every re-evaluation (re-occurrence of #5673, 1.167.50) #7285: vitejs/vite@235140b2d

[ulrichstark]

I have the same issue. Since @tanstack/react-start 1.168.7 the dev server fails immediately with "TypeError: (0 , vite_ssr_import_0.createMiddleware) is not a function". The previous version 1.168.6 doesn't crash the dev server. I can attempt to create a minimal reproducing project if needed, but this probably requires a few hours of work.

[VintageWander]

I have a similar error it seems like

error: (0,__vite_ssr_import_1__.createMiddleware) is not a function. (In '(0,__vite_ssr_import_1__.createMiddleware)({ type: "request" })', '(0,__vite_ssr_import_1__.createMiddleware)' is undefined)
     status: 500,
 statusText: undefined,
    headers: undefined,
       data: undefined,
       body: undefined,
  unhandled: true,

      at anonymous (/Users/wander/Code/RecruitConnect/src/modules/auth/middlewares/auth.ts:12:66)
      at processTicksAndRejections (native:7:39)

 7 |   const session = getCookie("session");
 8 | 
 9 |   if (!session) throw redirect({ to: "/auth/login" });
10 | 
11 |   const record = await db
12 |     .selectFrom("sessions")
                                                                      ^
TypeError: (0,__vite_ssr_import_1__.createMiddleware) is not a function. (In '(0,__vite_ssr_import_1__.createMiddleware)({ type: "request" })', '(0,__vite_ssr_import_1__.createMiddleware)' is undefined)
      at anonymous (/Users/wander/Code/RecruitConnect/src/modules/auth/middlewares/auth.ts:12:66)
      at processTicksAndRejections (native:7:39)

import { redirect } from "@tanstack/react-router";
import { createMiddleware } from "@tanstack/react-start";
import { deleteCookie, getCookie } from "@tanstack/react-start/server";
import { db } from "@/global/libraries/database";

export const authMiddleware = createMiddleware({ type: "request" }).server(async ({ next }) => {
  const session = getCookie("session");

  if (!session) throw redirect({ to: "/auth/login" });

  const record = // ...

  if (!record) {
    deleteCookie("session");
    throw redirect({ to: "/auth/login", replace: true });
  }

  return next({
    context: {
      user: {
        id: record.user_id,
        token: record.token,
      },
    },
  });
});

server.ts

// src/server.ts
import handler, { createServerEntry } from "@tanstack/react-start/server-entry";

export default createServerEntry({
  fetch(request) {
    return handler.fetch(request);
  },
});

This error happens on @tanstack/react-start version 1.168.7 onwards (.8, .9), I pin the version back to 1.168.6 everything works normally

[schiller-manuel]

this needs an upstream fix in vite: vitejs/vite#22493

[schiller-manuel]

i added a potential workaround in start, can you please try out https://github.com/TanStack/router/releases/tag/release-2026-05-21-2113

[pdlug]

The workaround resolved the issue for me.

[ulrichstark]

i added a potential workaround in start, can you please try out https://github.com/TanStack/router/releases/tag/release-2026-05-21-2113

After upgrading to @tanstack/react-start 1.168.10, I get the following error when starting the dev server:

Reloading once in the browser shows me my application with no error.
I will wait for the upstream Vite fix and then try upgrading Tanstack Start again.