Importing from a linked local ES modules package using the package name works with “main” property but fails with “module”

[OfirD1]

Version

15.13.0

Platform

Microsoft Windows NT 10.0.19041.0 x64

Subsystem

No response

What steps will reproduce the bug?

To reproduce, do the following:

1. exporter: A Node.js package which is an ES module that exports something (e.g., using export default).
2. importer: A Node.js module that tries to import what exporter exports, using import something from 'exporter'.
3. Use npm link to locally link exporter to importer.

Then:

• The setup runs successfully if exporter's package.json uses the main property.
• The setup run fails if exporter's package.json uses the module property.
  • This failure can be "fixed" by using import something from 'exporter/dist/bundle.js', but that's unacceptable.

Example Code

exporter

|- webpack.config.js
|- package.json
|- /src
  |- index.js
|- /dist
  |- bundle.js

webpack.config.js:

import path from "path";
import { fileURLToPath } from "url";

const __dirname = path.dirname(fileURLToPath(import.meta.url));

export default {
  mode: "development",     
  entry: "./src/index.js",
  output: {
    filename: "bundle.js",
    path: path.resolve(__dirname, "dist"),
    library: {
      type: "module",
    },
  },
  experiments: {
    outputModule: true,
  },
};

package.json:

{
  "name": "exporter",
  "version": "1.0.0",
  "main": "dist/bundle.js", <-- *** NOTE THIS LINE ***
  "scripts": {
    "build": "webpack"
  },
  "devDependencies": {
    "webpack": "^5.51.1",
    "webpack-cli": "^4.8.0"
  },
  "type": "module"
}

index.js:

function util() {
  return "I'm a util!";
}
export default util;

importer

|- package.json
|- /src
  |- index.js

package.json

{
  "name": "importer",
  "version": "1.0.0",
  "type": "module"
}

index.js

import util from 'exporter';

console.log(util());

Then:

1. Linking:

⚡  cd exporter
⚡  npm link
⚡  cd importer
⚡  npm link exporter

2. Executing:

⚡  node importer.js 
I'm a util!

However, if exporter's package.json is changed to:

{
  "name": "exporter",
  "version": "1.0.0",
  "module": "dist/bundle.js", <-- *** NOTE THIS LINE ***
  "scripts": {
    "build": "webpack"
  },
  "devDependencies": {
    "webpack": "^5.51.1",
    "webpack-cli": "^4.8.0"
  },
  "type": "module"
}

Then:

2. Executing:

⚡  node importer.js 

Fails:

Error [ERR_MODULE_NOT_FOUND]: Cannot find package 'importer\node_modules\exporter\' imported from importer\src\index.js

How often does it reproduce? Is there a required condition?

No response

What is the expected behavior?

Node.js should run successfully on both cases

What do you see instead?

Node.js fails to import from a linked package if the latter has the module property set.

Additional information

This was also posted as an SO question, frankly my guess is that's not a bug but I can't be sure.

[aduh95]

As you can see in its package.json documentation, Node.js does not support the "module" field – it simply ignores it. Instead, you need to use the "main" field, and/or the "exports" field. You can check out Package entry points section of the docs to get more info on that.

This is indeed not a bug but working as expected, unless you think we can improve this docs to make the information clearer, I think we can close this issue.