Exporting in CommonJS

Create a file called math.js:

function add(a, b) {
  return a + b;
}
  
function subtract(a, b) {
  return a - b;
}
  
// Export functions
module.exports = { add, subtract };

Importing in CommonJS

In app.js, import the module using require():

const math = require("./math");

console.log(math.add(5, 3)); // Outputs: 8
console.log(math.subtract(10, 4)); // Outputs: 6

Exporting a Single Value

module.exports = function (name) {
  return `Hello, ${name}!`;
};

Importing a single exported function:

const greet = require("./greet");
console.log(greet("Alice")); // Outputs: Hello, Alice!

ES6 Modules (ESM)

ES6 Modules are the modern way to work with modules in JavaScript. They use export and import and work in both browsers and Node.js (with "type": "module" in package.json).

Named Exports

Create math.js:

export function add(a, b) {
  return a + b;
}
  
export function subtract(a, b) {
  return a - b;
}

Default Exports

Only one default export per file:

export default function multiply(a, b) {
  return a * b;
}

Importing in ES6 Modules

Importing Named Exports

In app.js:

import { add, subtract } from "./math.js";

console.log(add(5, 3)); // Outputs: 8
console.log(subtract(10, 4)); // Outputs: 6

Importing a Default Export

import multiply from "./math.js";
console.log(multiply(4, 5)); // Outputs: 20

Importing Everything from a Module

import * as math from "./math.js";

console.log(math.add(2, 3));
console.log(math.subtract(7, 2));

Using ES6 Modules in Node.js

To use ES6 modules in Node.js, add "type": "module" in package.json:

Then, use import instead of require().

import { add } from "./math.js";
console.log(add(10, 5));

Differences Between CommonJS and ES6 Modules

FeatureCommonJS (require)ES6 Modules (import)Default inNode.jsModern JavaScript (ES6)Syntaxrequire() / module.exportsimport / exportLoad TypeSynchronousAsynchronousCan be used in BrowsersNo (without bundlers)Yes (Supported in modern browsers)

When to Use Which?

• Use CommonJS for Node.js applications that do not require modern JavaScript syntax.

• Use ES6 Modules for modern JavaScript projects, browsers, and future-proof development.

Conclusion

Modules improve code reusability and organization. ES6 Modules (import/export) are the standard for modern JavaScript, while CommonJS (require/module.exports) is still widely used in Node.js. The next section will cover working with databases in JavaScript, focusing on connecting Node.js to relational and NoSQL databases.