02 - Introduction to Node.js

• nodejs
• by Sn0wAlice

Introduction

Node.js is a runtime environment that allows JavaScript to run outside the browser. It is built on Google’s V8 JavaScript Engine and is commonly used for backend development.

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1. What is Node.js?

• Node.js is asynchronous, event-driven, and non-blocking.
• It uses the V8 engine, which converts JavaScript into machine code for fast execution.
• It enables server-side scripting, allowing JavaScript to run on a server.

Example:

console.log("Hello, Node.js!");

Run this file with:

node filename.js

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2. Installing Node.js

Step 1: Download & Install

• Visit Node.js official website
• Choose LTS (Long-Term Support) version.
• Verify installation:

node -v
npm -v

Step 2: Using Node REPL

The Node.js Read-Eval-Print-Loop (REPL) allows executing JavaScript interactively:

node
> console.log("Hello");

Exit REPL by pressing Ctrl + C twice.

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3. Understanding the Node.js Architecture

Key Features:

• Single-threaded, non-blocking
• Uses event-driven architecture
• Supports asynchronous programming

The Event Loop

The event loop enables asynchronous execution in Node.js.

console.log("Start");
setTimeout(() => console.log("Delayed"), 2000);
console.log("End");

Output:

Start
End
Delayed

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4. Working with Core Modules

Node.js provides built-in modules like:

• fs (File System) – Work with files.
• http – Create servers.
• path – Handle file paths.
• os – Get OS-related information.
• events – Work with event-driven programming.

Example: Using fs module

const fs = require("fs");
fs.writeFileSync("test.txt", "Hello, Node.js!");
console.log("File written!");

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5. Creating a Basic Web Server

Node.js can create HTTP servers without external frameworks.

const http = require("http");
const server = http.createServer((req, res) => {
    res.writeHead(200, { "Content-Type": "text/plain" });
    res.end("Hello, World!");
});
server.listen(3000, () => console.log("Server running on port 3000"));

Run with:

node server.js

Visit http://localhost:3000 in your browser.

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6. Using External Packages with NPM

• NPM (Node Package Manager) allows installing third-party modules.
• Example: Install Express.js framework

npm install express

• Check installed packages:

npm list --depth=0

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7. Working with Asynchronous Code

Callbacks:

const fs = require("fs");
fs.readFile("test.txt", "utf8", (err, data) => {
    if (err) throw err;
    console.log(data);
});

Promises & Async/Await:

const fsPromises = require("fs/promises");
async function readFile() {
    const data = await fsPromises.readFile("test.txt", "utf8");
    console.log(data);
}
readFile();

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🏆 Exercises

• 1. Verify your Node.js and NPM installation.
• 2. Create and run a simple script that prints your name in Node.js.
• 3. Create a file using the fs module and write some text to it.
• 4. Build a simple HTTP server that returns JSON data.
• 5. Install a package using NPM and use it in your script.

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Conclusion

Node.js is a powerful runtime for executing JavaScript outside the browser. Understanding its core modules, event loop, and async features is essential before moving to frameworks like Express.js.

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