ESM in extensionless executable files (`import` statement inside dependency chain)

test_bin

#!/usr/bin/env node

/**
* This is a POC of https://github.com/nodejs/modules/issues/152#issuecomment-1068515887
*
* The requires statement below should fail with an error while
* using an ESM import buried inside the module dependency chain:
*   import crypto from 'crypto';
*   ^^^^^^
* SyntaxError: Cannot use import statement outside a module
*/
console.log('Running `./test_bin` (extensionless binary)..');

console.log('Loading `./test_lib.js` (internal library)..');
const app = require('./test_lib.js');

test_lib.js

console.log('Loading `./test_lib_dep.js` (internal dependency)..');

const dep = require('./test_lib_dep.js');

module.exports = dep;

test_lib_dep.js

/**
 * This dependency is buried several levels deep inside the module depdendency chain
 * thus highlighting the fact that ESM `import` statements cannot always be controlled
 * by the calling code.
 */

import crypto from 'crypto';

console.log('Printing some random bytes: %s', crypto.randomBytes(10));

Right, but that's because test_lib.js is CJS, so test_lib_dep needs to have an .mjs extension.