,

CommonJS

CommonJS modules can use the require.main object to determine whether the module is executed directly or imported. The require.main object is the main module that started your Node.js application.

// CommonJS

// main.js
if (require.main === module) {
  // This script is being run directly
  console.log('This script is the main module.');
} else {
  // This script is being imported as a module
  console.log('This script is being imported as a module.');
}

In this example, if you run main.js directly using the main.js node, you will see the output This script is the main module. When I import main.js into another script or module using require('./main') I get the output This script will be imported as a module.

Note that this approach works with Node.js versions that support ES Module (ESM) syntax.

If you are using CommonJS syntax, you may want to use the require.main === module check.

ESM

In the ECMAScript Module (ESM), you can use the "import.meta" object to determine whether a module is executed directly or imported. In particular, you can check the import.meta.url property.

// main.mjs
if (import.meta.url === `file://${process.argv[1]}`) {
  // This module is being run directly
  console.log('This module is the main module.');
} else {
  // This module is being imported as a module
  console.log('This module is being imported as a module.');
}

or you can using module es-main:

// ESM

import esMain from 'es-main';

if (esMain(import.meta)) {
    console.log('called directly');
} else {
    console.log('required as a module');
}

In this example, if you run main.mjs directly using the main.mjs node, you will see the output: "This module is the main module.
" If you import main.mjs into another ESM module using import './main.mjs';, you will see the output This module will be imported as a module. Note the ESM file extension.

Modules are usually .mjs. If you want to use CommonJS syntax, you can use the approach described in the previous answer ("require.main === module").