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Getting Started with Node.js

What is Node.js?

Node.js is an open-source, cross-platform JavaScript runtime environment built on Chrome's V8 engine. It allows you to run JavaScript on the server side, enabling you to build fast, scalable network applications.

Why Choose Node.js?

• JavaScript Everywhere: Use the same language for frontend and backend.
• High Performance: Built on V8, which compiles JS to native machine code.
• Non-blocking I/O: Handles thousands of concurrent connections with a single thread.
• Rich Ecosystem: NPM provides over 2 million packages.
• Active Community: Backed by OpenJS Foundation and major companies.

System Requirements

• Operating System: Linux, macOS, or Windows
• Memory: Minimum 512 MB RAM (1 GB recommended)
• Disk Space: At least 200 MB for Node.js and NPM
• Node.js Version: LTS (Long Term Support) recommended

Node.js vs Browser JavaScript

Aspect	Browser	Node.js
Global Object	window	global
DOM/BOM	Available	Not available
Module System	ES Modules (import/export)	CommonJS + ES Modules
File System	No access	Full access (fs module)
Runtime	Sandboxed	Full system access

Command Line Basics

Node.js is primarily used through the command line. Here are essential commands:

# Check Node.js version
node --version

# Run a JavaScript file
node app.js

# Start REPL (interactive shell)
node

# Run with inspector for debugging
node --inspect app.js

# Execute a one-liner
node -e "console.log('Hello, Node!')"

The V8 Engine

V8 is Google's open-source high-performance JavaScript engine, written in C++. It compiles JavaScript directly to native machine code using JIT (Just-In-Time) compilation. Node.js embeds V8 to execute JavaScript on the server.

Node.js Architecture

Node.js consists of three main layers:

1. JavaScript (V8): Handles your application code and core JS execution.
2. Node API (libuv): Provides asynchronous I/O operations like file system, networking, and concurrency.
3. Event Loop: Coordinates callbacks and ensures non-blocking execution.

The Event Loop

The event loop is what allows Node.js to perform non-blocking I/O operations despite JavaScript being single-threaded. It works by offloading operations to the system kernel whenever possible.

The event loop has several phases:

• Timers: Executes callbacks scheduled by setTimeout() and setInterval().
• I/O Callbacks: Executes almost all callbacks except timers, close, and setImmediate.
• Idle/Prepare: Used internally by Node.js.
• Poll: Retrieves new I/O events and executes their callbacks.
• Check: Executes setImmediate() callbacks.
• Close Callbacks: Executes close event callbacks (e.g., socket.on('close')).

Prerequisites

Before diving deeper, ensure you have:

• Basic knowledge of JavaScript (variables, functions, loops, objects)
• Familiarity with command line / terminal
• Node.js installed (download from nodejs.org)
• A code editor (VS Code recommended)

Your First Node.js Application

Create a file named hello.js and add:

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

// Access process info
console.log("Node version:", process.version);
console.log("Platform:", process.platform);
console.log("Current directory:", process.cwd());

Run it with: node hello.js