Express hosting on Vercel

Help
1

I am trying to host an express js app with better-auth, it used to give me this error -

2025-10-28T04:22:13.659Z [error] Error [ERR_REQUIRE_ESM]: require() of ES Module /var/task/node_modules/jose/dist/webapi/index.js from /var/task/node_modules/@better-auth/core/dist/oauth2/index.cjs not supported.
Instead change the require of index.js in /var/task/node_modules/@better-auth/core/dist/oauth2/index.cjs to a dynamic import() which is available in all CommonJS modules.
    at /opt/rust/nodejs.js:2:13528
    at Function.Vr (/opt/rust/nodejs.js:2:13906)
    at Ue.e.<computed>.Be._load (/opt/rust/nodejs.js:2:13498)
    at TracingChannel.traceSync (node:diagnostics_channel:322:14) {
  code: 'ERR_REQUIRE_ESM'
}

I tried to import it dynamically, but is that the best solution we got?

2

If you’re having trouble deploying an Express app, this guide can help.

You can also ask v0 for suggestions tailored to your own project setup.

4

Hey @gyanendra-7337!

Thanks for joining us here from X, glad we’ve got more context now :blush:

Looks like this error’s happening because your project is mixing CommonJS and ES modules. The jose package is ESM-only, but @better-auth/core is trying to import it using CommonJS (require()), which causes the issue.

Here’s what you can try…

1. Convert your project to ES modules (recommended)

  • Add "type": "module" to your package.json
  • Replace all require() calls with import
  • Make sure to include .js extensions in your imports

This is the cleanest long-term fix and should solve the compatibility issue entirely.

2. Check your better-auth setup

  • Make sure you’re on the latest version of better-auth
  • Check if they have Vercel deployment notes or examples

3. Set your Node.js runtime on Vercel

If you’re using serverless functions, you can explicitly set the runtime:

{
  "functions": {
    "app.js": {
      "runtime": "nodejs18.x"
    }
  }
}

If you’re on Next.js with the App Router, try using an Edge Function or Server Action, which support ES modules out of the box.

5

@pawlean Thanks for this, crazy support from you.
Thanks a lot

1 Like
6

Do you have any idea what tsconfig properties we need to set to add file extensions on build?

7

Glad I could be of help! What I’m here for :slight_smile:

Try updating your tsconfig.json like this:

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "ESNext",
    "moduleResolution": "Bundler",
    "esModuleInterop": true,
    "resolveJsonModule": true,
    "skipLibCheck": true,
    "outDir": "dist"
  }
}

Then either:

  • Manually include .js in your imports (e.g. import { x } from './utils.js'), or
  • Run a tool like tsc-esm-fix after tsc to automatically add file extensions.

TypeScript itself won’t rewrite the paths, so tsc-esm-fix is the simplest way to make your ESM output work cleanly on Vercel.