Configure Vercel to treat a compiled index.js as a serverless function

[davi-ldc]

I’m working on a monorepo with the following setup:

• index.ts (using the Hono framework with hono/vercel) is compiled using tsup into dist/functions/index.js
• Static assets are built with Vite into dist/vite/assets

So my build structure ends up like this:

dist/
├── functions/
│   └── index.js ← this is my API handler
└── vite/
    └── assets/

My vercel.json looks like this:

{
  "$schema": "https://openapi.vercel.sh/vercel.json",
  "version": 2,
  "installCommand": "pnpm install",
  "buildCommand": "pnpm turbo run build",
  "outputDirectory": "dist",
  "rewrites": [
    {
      "source": "/assets/(.*)",
      "destination": "/dist/vite/assets/$1"
    },
    {
      "source": "/(.*)",
      "destination": "/dist/functions/index.js"
    }
  ]
}

Even though I set up a rewrite to /functions/index.js, Vercel is treating the file as a static asset instead of a serverless function. The file is publicly available (e.g. site.vercel.app/functions/index.js) but it’s not executed as a function.

I tried changing the tsup output to api/index.js instead (since Vercel treats files inside the /api directory as functions). But that didn’t work, the api/index.js file didn’t show up in the Vercel deployment output. I guess that Vercel doesn’t allow emitting files outside of the declared “outputDirectory” (which is dist), so writing to ../api is being ignored.

Question:

Is there a supported way to include a compiled serverless function in the output directory and still have Vercel treat it as a serverless function?

Or, is there a way to output a file to /api at the root level (outside outputDirectory) so Vercel recognizes it?

[anshumanb (Anshuman Bhardwaj)]

Hi @davi-ldc, welcome to the Vercel Community!

So, it seems like the way your build outputs are generated they are treated as static assets.

Have you tried using the Vercel - Hono adapter?

If you need more help, please share your public repo or a minimal reproducible example. That will let us all work together from the same code to figure out what’s going wrong.

[davi-ldc]

Hey Anshuman, thanks for the reply!

Sorry for the lack of information. I made a minimal example repo to reproduce the issue:

GitHub - Davi-ldc/vercel-exemple

If you try deploying it to Vercel and select the app/ folder as root, all the output files (including dist/functions/index.js that should be a serverless function) get treated as static assets instead.