Discover Node.js

Learning Objectives

• Understand Node.js and its purpose
• Learn about modules and packages
• Master npm (Node Package Manager)
• Create reusable code modules
• Build applications with Node.js

Section 25.1: Introducing Node.js

What is Node.js?

JavaScript runtime for executing code outside the browser (servers, CLIs, tools).

Why Node.js?

• Server-side JavaScript
• Non-blocking I/O
• Fast execution
• Large ecosystem (npm)
• Same language everywhere (JavaScript)

Installing Node.js

# Check Node and npm versions
node --version
npm --version

# Run JavaScript file
node filename.js

Your First Node.js Program

// hello.js
console.log("Hello from Node.js!");

let message = "Welcome to server-side JavaScript";
console.log(message);

// Math operations work the same
console.log(2 + 3);  // 5

Section 25.2: Node.js Modules

Built-in Modules

// File system
const fs = require("fs");
let content = fs.readFileSync("file.txt", "utf8");

// Path utilities
const path = require("path");
let filename = path.basename("/path/to/file.txt");

// Operating system info
const os = require("os");
console.log(os.platform());  // "linux"

// URL parsing
const url = require("url");
let parsed = url.parse("https://example.com?id=1");

Creating a Module

// math.js
function add(a, b) {
    return a + b;
}

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

module.exports = {
    add: add,
    subtract: subtract
};

Using Your Module

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

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

Section 25.3: Exporting a Class or Object

Exporting a Class

// Dog.js
class Dog {
    constructor(name, breed) {
        this.name = name;
        this.breed = breed;
    }

    bark() {
        console.log(this.name + " barks!");
    }
}

module.exports = Dog;

Using the Class

// app.js
const Dog = require("./Dog");

let myDog = new Dog("Rex", "Golden Retriever");
myDog.bark();  // Rex barks!

Exporting Multiple Items

// utils.js
const formatDate = (date) => new Date(date).toISOString();

const formatCurrency = (amount) => "
quot; + amount.toFixed(2);

const capitalize = (str) => str.charAt(0).toUpperCase() + str.slice(1);

module.exports = {
    formatDate,
    formatCurrency,
    capitalize
};

Section 25.4: Node.js Packages

npm (Node Package Manager)

# Initialize new project
npm init -y

# Install a package
npm install express
npm install --save-dev nodemon

# List installed packages
npm list

# Update packages
npm update

# Remove package
npm uninstall express

package.json

{
    "name": "my-app",
    "version": "1.0.0",
    "description": "My Node.js application",
    "main": "index.js",
    "scripts": {
        "start": "node index.js",
        "dev": "nodemon index.js"
    },
    "dependencies": {
        "express": "^4.17.1",
        "axios": "^0.21.1"
    },
    "devDependencies": {
        "nodemon": "^2.0.7"
    }
}

Using Installed Packages

// Using express
const express = require("express");
const app = express();

app.get("/", (req, res) => {
    res.send("Hello from Express!");
});

app.listen(3000, () => {
    console.log("Server running on port 3000");
});

Section 25.5: Package Management with NPM

Common npm Commands

# Save to dependencies
npm install express

# Save to dev dependencies
npm install --save-dev jest

# Install from package.json
npm install

# Global installation
npm install -g nodemon

# Update all packages
npm update

# Uninstall package
npm uninstall express

Coding Challenges

Challenge 25.1: Circles Again

Task: Create a Circle module with methods

Challenge 25.2: Accounting Module

Task: Create accounting utilities module

Challenge 25.3: Playing with Dates

Task: Create date formatting utilities

Key Takeaways

✅ Node.js runs JavaScript on servers
✅ Modules are reusable code files
✅ module.exports shares code
✅ require() imports modules
✅ npm manages dependencies
✅ package.json tracks project info

Quiz Questions

• What is Node.js?
• How do you export a module?
• How do you import a module?
• What is npm?
• What does package.json contain?

Next Module: Module 26 - Create a Web Server