Resolve '__dirname is Not Defined' Error in Node.js

When using ES modules ("type": "module") in Node.js, you may encounter the following error:

ReferenceError: __dirname is not defined in ES module scope

This error happens because ES modules don’t include the CommonJS global variables like __dirname and __filename. Let’s go over how to recreate them and understand what’s happening under the hood.

Understanding the “__dirname” Variable

In CommonJS, Node.js automatically defines two global variables:

• __filename — represents the absolute path of the current file.
• __dirname — represents the directory name of the current file.

However, in ES module scope, these variables are not defined because ES modules use import/export syntax and the URL-based module system, not file-based globals.

To fix this, you can extract the current file path using the import.meta.url property and the path module.

1. Define __dirname Manually in ES Modules

You can recreate __dirname and __filename manually using import.meta.url and path.dirname().

import { dirname } from 'path';
import { fileURLToPath } from 'url';

// Create __filename and __dirname from URL
const __filename = fileURLToPath(import.meta.url);
const __dirname = dirname(__filename);

console.log('Filename:', __filename);
console.log('Directory:', __dirname);

Explanation:

• import.meta.url gives the module’s URL.
• fileURLToPath() converts it into a file path.
• dirname() extracts the directory path.

Now, __dirname behaves the same as it does in CommonJS.

2. Remove "type": "module" to Use CommonJS

If you don’t need ES modules, the simplest fix is to remove "type": "module" from your package.json file.

{
  "type": "commonjs"
}

This switches your project back to CommonJS mode, where __dirname and __filename are automatically available as global variables.

3. Fixing __dirname in Webpack or Rollup

If your project is bundled for the browser, Node.js globals like __dirname don’t exist. To handle that safely, use bundler options.

Webpack Example

node: {
  __dirname: false,
  __filename: false
}

This prevents Webpack from replacing those variables incorrectly.

Rollup Example

In Rollup, you can add a plugin to define globals manually:

import replace from '@rollup/plugin-replace';

export default {
  plugins: [
    replace({
      preventAssignment: true,
      __dirname: JSON.stringify('/src'),
      __filename: JSON.stringify('/src/index.js')
    })
  ]
}

4. Why __dirname is Undefined in ES Module Scope

Unlike CommonJS, ES modules in Node.js use URLs, not file paths. This design improves interoperability with browsers but removes file-based globals like __dirname.

Key technical points:

• ES modules use the import.meta object instead of CommonJS globals.
• The module loader derives paths from URLs rather than the filesystem.
• Node.js intentionally does not provide __dirname to avoid ambiguity across environments.

If you need compatibility with file operations, always reconstruct __dirname manually.

5. Common Mistakes and Debug Tips

❌ Using __dirname directly in ESM code

console.log(__dirname);
// ReferenceError: __dirname is not defined

✅ Correct version

import { dirname } from 'path';
import { fileURLToPath } from 'url';
const __dirname = dirname(fileURLToPath(import.meta.url));
console.log(__dirname);

Pro Tip: When debugging path-related issues, log both the file URL and resolved path:

console.log(import.meta.url);
console.log(fileURLToPath(import.meta.url));

This helps confirm that the URL is being converted properly.

6. Related Concepts and Best Practices

Here’s a quick summary of related Node.js path utilities:

By combining these, you can manage file paths safely across ESM and CommonJS.

Summary

If you see “ReferenceError: __dirname is not defined in ES module scope”, here’s what to do:

1. Manually define __dirname using import.meta.url and path.dirname()
2. Remove "type": "module" to return to CommonJS
3. Configure your bundler (Webpack or Rollup) to handle file paths properly

By applying these methods, you can restore the familiar __dirname and __filename behavior — ensuring your Node.js projects run consistently in both CommonJS and ES module environments.