Modules

This lesson covers Modules. Let us learn this step by step — no rush, no jargon first.

What you will learn

• What modules means — in normal words, not textbook words
• How it works step by step
• Code you can run today on your laptop
• Where teams use this in real projects

Before you start

• Software: Node.js LTS from nodejs.org, VS Code, and a terminal
• Knowledge: Lessons 1–5 in this course
• Previous lesson: Node.js Runtime — Complete Guide

Explain it simply

Modules let you split code into files. You export from one file and require (or import) it in another.

Why developers use this

• Keep files small and focused
• Reuse logic across the project
• Avoid one giant app.js

How it works (step by step)

1. You write JavaScript in a .js file about Modules.
2. You run it with node filename.js in the terminal.
3. Node prints output or starts a server depending on the lesson.
4. You change one line, run again, and see what changed — that is how you learn.

Code example — type this yourself

// math.js
exports.add = (a, b) => a + b;

// app.js
const { add } = require('./math');
console.log(add(2, 3));

exports.add makes the function available. require('./math') loads it (note the ./ for local files).

What each part does

• // math.js — Line 1: runs as written.
• exports.add = (a, b) => a + b; — Line 2: runs as written.
• // app.js — Line 3: runs as written.
• const { add } = require('./math'); — Loads a built-in module or package you installed with npm.
• console.log(add(2, 3)); — Prints to the terminal — great for learning; use proper logging in production.

Real life: where Modules shows up

A startup team uses Modules when they bootstrap their first API. The developer runs a small script on a laptop, stores config in .env, and splits code into modules before the app grows. Start small: one feature working beats a perfect architecture on paper.

Try it yourself — hands-on

1. Create math.js and app.js in the same folder
2. Run node app.js — you should see 5
3. Add a subtract function and use it

Common mistakes (avoid these)

• require('math') without ./ — Node looks in node_modules, not your folder.

Interview note

Interviewers often ask: “What is Modules?” Answer in one sentence, then give a tiny example you actually ran.

Summary

• Use module.exports or exports to share code
• require loads CommonJS modules
• Local files need ./ prefix