Frameworkless serverless function import cannot find module

Help
1

I have a relatively simple setup that essentially bundles some source code and outputs to dist using esbuild. This works and I can see it in the output tab of my function.

However, when I attempt to import it from my serverless function in the api folder, i.e. “api/x.ts”, it cannot find the module.

The code itself is very simple for x.ts

export { GET } from "../handler.js"

with the output directory structure being:
api/
├─ x.js
├─ middleware
handler.js
middleware

This is running on node 22.x. I cannot determine why I cannot import handler.js from my serverless function. I’ve added “includeFiles”: “handler.js” to my vercel.json.

The actual error is:
Error [ERR_MODULE_NOT_FOUND]: Cannot find module ‘/var/task/handler.js’ imported from /var/task/api/x.js

Thank you

2

Resolved this after many different configurations of paths! A dynamic import was required and moreover the path was not “handler.js” but rather “dist/handler.js”.

I think this is a consequence of using vercel cli and having outputDir defined but not rootDir. Though the Vercel functions UI showing the output structure mentioned above is misleading, at least in this case.