Node.js Introduction

Last Updated : 12 Mar, 2026

Node.js is a runtime environment that allows JavaScript to run outside the browser for building server-side applications.

  • Built on the V8 JavaScript engine.
  • Supports asynchronous, event-driven programming.
  • Efficient for scalable network applications.
Nodejs
Nodejs

"Hello, World!" Program in Node.js

A “Hello, World!” program is the simplest way to begin with Node.js, showing how JavaScript runs outside the browser.

  • Executes JavaScript in a server or command-line environment.
  • Does not rely on a browser console.
JavaScript 
console.log("Hello, World!");

Output:

helloworld
Hello, World! in NodeJS

Features of Node.JS

  • Server-Side JavaScript: Runs JavaScript outside the browser for backend development.
  • Asynchronous & Non-Blocking: Handles multiple requests efficiently using an event-driven model.
  • Single-Threaded Event Loop: Manages concurrent tasks without thread overhead.
  • V8 Engine: Uses Google’s high-performance engine to execute JavaScript quickly.
  • Scalable & Lightweight: Suitable for microservices and high-traffic applications.
  • Rich NPM Ecosystem: Provides access to thousands of reusable open-source packages.

Working of Node.JS

Node.js is a runtime environment that enables JavaScript to run outside the browser for building scalable server-side applications.

  • Built on the V8 JavaScript engine.
  • Uses asynchronous, event-driven architecture.
  • Suitable for scalable network applications.

Single-Threaded Event Loop Model

Node.js operates on a single thread but efficiently handles multiple concurrent requests using an event loop.

  • Client Sends Request: Requests data, files, or database operations.
  • Event Loop Handles It: Non-blocking tasks are offloaded without stopping execution.
  • Background Processing: Node.js continues handling other requests.
  • Callback Executes: Response is returned once the task completes.
JavaScript 
const fs = require('fs');

fs.readFile('file.txt', 'utf8', (err, data) => {
    if (err) throw err;
    console.log(data); 
});

console.log("Reading file...");

Components of Node.js Architecture

Node.js architecture consists of components that work together to handle asynchronous, non-blocking operations efficiently.

  • V8 Engine: Compiles JavaScript to machine code for fast execution.
  • Event Loop: Manages asynchronous tasks without blocking the main thread.
  • Libuv: Handles I/O operations, thread pool, and timers.
  • Non-Blocking I/O: Executes tasks without waiting for previous ones to complete.

Use Cases of Node.js

Node.js is well suited for building high-performance, scalable, and real-time applications. Common use cases include:

  • Web APIs and Backend Services: Used to build RESTful APIs and GraphQL APIs and power backend services for web and mobile applications.
  • Real-Time Applications: Chat applications (e.g., WhatsApp, Slack). Live streaming services (e.g., Netflix, Twitch).
  • Microservices Architecture: Enables building scalable, independent services, commonly used in cloud-based applications.
  • IoT (Internet of Things) Applications: Handles real-time data streams from devices, making it suitable for smart homes and sensor-based systems.
  • Serverless Computing: Efficiently runs lightweight functions on cloud platforms like AWS Lambda and Azure Functions.
  • Single-Page Applications (SPAs): Supports React, Angular, and Vue.js apps by efficiently handling backend API requests.
  • Data-Intensive Applications: Handles real-time analytics and integrates well with NoSQL databases like MongoDB and Firebase.
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