Part 3 – Modules and NPM Demystified

Node.js’s module system and npm (Node Package Manager) are what make it so powerful. This guide will help you master these fundamental concepts.

1. Understanding Modules

Core Modules

Built into Node.js installation:

• fs – File system operations
• http – HTTP server/client
• path – File path utilities
• os – OS-related utilities

Custom Modules

Create your own reusable code:

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

2. Module Usage Patterns

Importing Core Modules

const fs = require('fs');

Importing Local Modules

const greet = require('./greet');
console.log(greet('Developer'));

ES Modules (Modern Approach)

import fs from 'fs';
import greet from './greet.js';

3. package.json Deep Dive

This file is the heart of every Node.js project. Here’s what you need to know:

Key Field	Purpose	Example
dependencies	Production required packages	"express": "^4.18.2"
devDependencies	Development-only packages	"nodemon": "^2.0.22"
scripts	Custom command shortcuts	"start": "node app.js"

4. Essential npm Commands

Package Installation

• npm install package – Local install
• npm install -g package – Global install
• npm install --save-dev package – Dev dependency

Project Management

• npm init – Create new project
• npm update – Update packages
• npm audit – Security check

5. Semantic Versioning Explained

Node.js packages follow semver (semantic versioning):

"dependencies": {
    "express": "^4.18.2",  // Compatible with 4.x.x
    "lodash": "~4.17.21", // Compatible with 4.17.x
    "mongoose": "5.13.16"  // Exact version only
}

Version Symbols: ^ = minor/patch updates, ~ = patch updates only, no symbol = exact version

6. Creating Your Own Module

Step-by-step guide to publishing:

1. Create your module code
2. Add proper package.json
3. Login to npm: npm login
4. Publish: npm publish

7. Best Practices

• Always specify exact versions in production (npm install --save-exact)
• Use .npmignore to exclude unnecessary files
• Regularly run npm outdated and npm update
• Consider using yarn or pnpm for large projects

Next: Building Your First Node.js Server →

npm Cheat Sheet

• npm list --depth=0 – View installed packages
• npm view package versions – See available versions
• npm uninstall package – Remove a package
• npm ci – Clean install (for CI/CD)