middlewareHandler is not a function

Help
1

Hello! I used new nodeMiddleware with canary build. Worked ok, I made some production deployments with it. After I created preview deployment it started to error in every middleware invocation with error

TypeError: middlewareHandler is not a function
    at /var/task/___next_launcher.cjs:116:30
    at AsyncLocalStorage.run (node:internal/async_local_storage/async_hooks:91:14)
    at withNextRequestContext (/var/task/___next_launcher.cjs:30:18)
    ...

I would expect it not to crash, Locally my builds doing great

I have

  experimental: {
    nodeMiddleware: true,
  },

and next.js version 15.3.0-canary.36

Next.js

2

Hey @kirill-x. There’s not enough info here for me to be sure of what’s causing the error. I wrote another post with some suggestions for what details are helpful to include.

Please take a look and then add whatever you can here to help the rest of us see what’s going wrong :folded_hands:

1 Like
3

Hey! Im not sure what details are needed for this issue.
Here is error that is displayed instead of my preview website on the routes, that are triggering middleware

500: INTERNAL_SERVER_ERROR
Code: MIDDLEWARE_INVOCATION_FAILED
ID: arn1::2jvf2-1744869020703-69d318d20d0b

This is the full stacktrace from logs on vercel dashboard

TypeError: middlewareHandler is not a function
    at /var/task/___next_launcher.cjs:116:30
    at AsyncLocalStorage.run (node:internal/async_local_storage/async_hooks:91:14)
    at withNextRequestContext (/var/task/___next_launcher.cjs:30:18)
    at Object.serve [as handlerWeb] (/var/task/___next_launcher.cjs:113:18)
    at Object.handler (/opt/rust/nodejs.js:2:14544)
    at Server.<anonymous> (/opt/rust/nodejs.js:2:1716)
    at /opt/rust/nodejs.js:16:6144
    at AsyncLocalStorage.run (node:internal/async_local_storage/async_hooks:91:14)
    at /opt/rust/nodejs.js:16:6132
    at AsyncLocalStorage.run (node:internal/async_local_storage/async_hooks:91:14)

this is deployment ID

dpl_9MXV9H295nB8ZRonuNrUNqnmQKLc

What else could I share to help debug this issue?

4

Thanks for sharing the error info and deployment id. From what I can see in the logs, it looks like that build used an older Next.js canary version. Does the TypeError still happen if you switch to either latest or canary to make sure the most recent updates are included?

5

I had in package.json exact version that currently works fine in production deployment.
I updated version in preview branch to canary now, error is still there.

6

Are you able to share a minimal reproducible example or code snippets to show the middleware and routes triggering it?

7

Hi! I’m also using next js canary version and got the same error. May I ask for updates? Have you figure it out?

8

Never mind. I figured it out, hahaha. I moved my middleware.ts file inside the app folder. Previously, it was located in the root directory, and there was no problem with that locally, but Vercel couldn’t detect it. It seems Vercel can only detect it if it’s inside the app folder. That solved it for me.

9

I dont think I can make an example. I merged my branch to main and now problem is gone. Not sure what it was by it is related to how vercel treat barnch deploymnets

10

The main difference between preview deployments and production is whether NODE_ENV=production or not by default

You can try setting that explicitly in your environment variables to override and see if that helps you reproduce the scenario

If it is an issue that only breaks when in non-production, then double check whether your Next modules are in regular “dependencies” or “devDependencies”

1 Like
11

now this error randomly appeared in production branch after last deployment. It now block release version of the website

Project ID prj_uLlosTk50TCeFeq8nlxbCBAJnDeK

12

Getting exact same error on 10.4.0 canary 9

13

I had to stop using nodejs as middleware because of this error. It seem random and untracable as it only happens in vercel cloud platform

14

Still an issue on. Any update on this?

TypeError: middlewareHandler is not a function
    at /var/task/___next_launcher.cjs:116:30
    at AsyncLocalStorage.run (node:async_hooks:346:14)
    at withNextRequestContext (/var/task/___next_launcher.cjs:30:18)
    at Object.serve [as handlerWeb] (/var/task/___next_launcher.cjs:113:18)
    at Object.handler (/opt/rust/nodejs.js:2:14544)
    at Server.<anonymous> (/opt/rust/nodejs.js:2:1716)
    at /opt/rust/nodejs.js:16:6144
    at AsyncLocalStorage.run (node:async_hooks:346:14)
    at /opt/rust/nodejs.js:16:6132
    at AsyncLocalStorage.run (node:async_hooks:346:14)
15

Getting the same issue. it’s related to node middleware.