CommonJS vs ESM differences in Node.js - Hands-On Comparison

CommonJS vs ESM Differences in Node.js

📖 Scenario: You are building a simple Node.js project that uses modules to organize code. You want to understand the difference between CommonJS and ESM (ECMAScript Modules) by creating examples of each and seeing how to export and import functions.

🎯 Goal: Build two small modules: one using CommonJS syntax and one using ESM syntax. Then import and use these modules in separate main files to see how the syntax differs.

📋 What You'll Learn

Create a CommonJS module file named mathCommonJS.js that exports a function add which adds two numbers.

Create an ESM module file named mathESM.mjs that exports a function multiply which multiplies two numbers.

Create a CommonJS main file named index-cjs.js that imports and uses the add function from the CommonJS module and an ESM main file named index-esm.mjs that imports and uses the multiply function from the ESM module.

Use require() to import the CommonJS module and import statement to import the ESM module.

Ensure the project runs correctly with Node.js 20+.

💡 Why This Matters

🌍 Real World

Node.js projects often use modules to organize code. Understanding CommonJS and ESM helps you work with different libraries and write modular code.

💼 Career

Many Node.js jobs require knowledge of module systems to maintain and build scalable applications. Knowing how to switch between CommonJS and ESM is valuable.

1

Create CommonJS module with add function

Create a file named mathCommonJS.js and write a function called add that takes two parameters a and b and returns their sum. Export this function using module.exports.

Node.js

// Your code here

Need a hint?

Use module.exports = { add }; to export the function in CommonJS.

2

Create ESM module with multiply function

Create a file named mathESM.mjs and write a function called multiply that takes two parameters a and b and returns their product. Export this function using the export keyword.

Node.js

// Your code here

Need a hint?

Use export function multiply(a, b) { ... } to export the function in ESM.

3

Import CommonJS module in index-cjs.js

Create a file named index-cjs.js. Import the add function from mathCommonJS.js using require(). Call add(2, 3) and store the result in a variable called sum. Log the sum to the console.

Node.js

// Your code here

Need a hint?

Use const { add } = require('./mathCommonJS.js'); to import the CommonJS module.

4

Import ESM module in index-esm.mjs

Create a file named index-esm.mjs. Import the multiply function from mathESM.mjs using the import statement. Call multiply(4, 5) and store the result in a variable called product. Log the product to the console.

Node.js

// Your code here

Need a hint?

Use import { multiply } from './mathESM.mjs'; to import the ESM module.