Node.js "ERR_UNSUPPORTED_DIR_IMPORT" During Build in CI

In ESM, importing a directory does not implicitly load its index.js the way CommonJS does. An import that points at a folder throws ERR_UNSUPPORTED_DIR_IMPORT.

What this error means

After moving to "type": "module" or running a built ESM bundle, a directory-style import fails in CI even though the same path worked under CommonJS.

node

Error [ERR_UNSUPPORTED_DIR_IMPORT]: Directory import
'/work/repo/dist/utils' is not supported resolving ES modules imported
from /work/repo/dist/index.js
  code: 'ERR_UNSUPPORTED_DIR_IMPORT'

Common causes

Importing a folder under ESM

ESM requires a fully specified file path. import x from "./utils" resolves a directory and is rejected; CommonJS used to silently load utils/index.js.

Build output kept extensionless directory imports

A compiler configured for CommonJS-style resolution emitted directory imports that are invalid for the ESM runtime.

How to fix it

Import the explicit index file

Reference the file directly, including its extension, so the ESM resolver has an exact target.

src/index.js

// before
import { fn } from './utils';
// after
import { fn } from './utils/index.js';

Configure the compiler for Node ESM resolution

Set TypeScript module resolution to a Node ESM mode so it emits and checks fully specified paths.

tsconfig.json

{
  "compilerOptions": {
    "module": "NodeNext",
    "moduleResolution": "NodeNext"
  }
}

How to prevent it

Always use fully specified file paths (with extensions) in ESM source.
Use module/moduleResolution of NodeNext so the compiler enforces ESM paths.
Run the built ESM bundle in CI, not just the dev/transpile path.