How to fix Error: module.exports is undefined (trying to use exported value that doesn't exist) in Node.js

// Wrong - exports assigned in callback
const fs = require('fs');
fs.readFile('config.json', (err, data) => {
  module.exports = JSON.parse(data); // Too late!
});

// Correct - exports assigned immediately
const config = require('./config-loader');
module.exports = config;

// Export a function that returns a promise
module.exports = async function loadConfig() {
  const data = await fs.promises.readFile('config.json');
  return JSON.parse(data);
};

// module.js
function myFunction() { return 'hello'; }
function anotherFunction() { return 'world'; }

// Export both functions
module.exports = { myFunction, anotherFunction };

// main.js
const { myFunction, anotherFunction } = require('./module');
console.log(myFunction()); // 'hello'

// Wrong - trying to destructure single export
const { myFunction } = require('./module'); // undefined!

// Correct - import the whole export
const myFunction = require('./module');

// Wrong - reassignment loses previous properties
module.exports.foo = 'bar';
module.exports.baz = 'qux';
module.exports = { newValue: 'test' }; // foo and baz are now gone!

// Correct - set all properties at once
module.exports = {
  foo: 'bar',
  baz: 'qux',
  newValue: 'test'
};

// Or add properties without reassignment
exports.foo = 'bar';
exports.baz = 'qux';
exports.newValue = 'test';

{
  "type": "module"  // ES Modules
}

// ES Module syntax
export const myFunction = () => 'hello';
export default myFunction;

// Import
import myFunction, { myFunction as named } from './module.js';

// CommonJS syntax
module.exports = { myFunction };

// Import
const { myFunction } = require('./module');

// Clear cache for a specific module (development only)
delete require.cache[require.resolve('./module')];

// Then require again
const myModule = require('./module');

npm run build
node dist/index.js