NodeJS Introduction

Last Updated : 21 Feb, 2025

NodeJS is a runtime environment for executing JavaScript outside the browser, built on the V8 JavaScript engine. It enables server-side development, supports asynchronous, event-driven programming, and efficiently handles scalable network applications.

NodeJS is single-threaded, utilizing an event loop to handle multiple tasks concurrently.
It is asynchronous and non-blocking, meaning operations do not wait for execution to complete.
The V8 engine compiles JavaScript to machine code, making NodeJS fast and efficient.

Hello, World!” Program in NodeJS

A “Hello, World!” program is the simplest way to get started with NodeJS. Unlike the browser, where JavaScript runs inside the console, NodeJs executes JavaScript in a server environment or via the command line.

console.log("Hello, World!");

Output:

Hello, World! in NodeJS

Key Features of NodeJS

Server-Side JavaScript: NodeJS allows JavaScript to run outside the browser, enabling backend development.
Asynchronous & Non-Blocking: Uses an event-driven architecture to handle multiple requests without waiting, improving performance.
Single-Threaded Event Loop: Efficiently manages concurrent tasks using a single thread, avoiding thread overhead.
Fast Execution: Powered by the V8 JavaScript Engine, NodeJS compiles code directly to machine code for faster execution.
Scalable & Lightweight: Ideal for building microservices and handling high-traffic applications efficiently.
Rich NPM Ecosystem: Access to thousands of open-source libraries through Node Package Manager (NPM) for faster development.

How NodeJS Works?

NodeJS is a runtime environment that allows JavaScript to run outside the browser. It is asynchronous, event-driven, and built on the V8 JavaScript engine, making it ideal for scalable network applications.

Single-Threaded Event Loop Model

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

Client Sends a Request: The request can be for data retrieval, file access, or database queries.
NodeJS Places the Request in the Event Loop: If the request is non-blocking (e.g., database fetch), it is sent to a worker thread without blocking execution.
Asynchronous Operations Continue in Background: While waiting for a response, NodeJS processes other tasks.
Callback Execution: Once the operation completes, the callback function executes, and the response is sent back to the client.

const fs = require('fs');

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

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

Components of NodeJS Architecture

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.

Where to Use NodeJS?

NodeJS is best suited for applications that require high performance, scalability, and real-time processing. Below are some common use cases:

Web APIs and Backend Services : Ideal for building RESTful APIs and GraphQL APIs. It also Used in backend services for mobile apps and web applications.
Real-Time Applications: Chat applications (e.g., WhatsApp, Slack). Live streaming services (e.g., Netflix, Twitch).
Microservices Architecture: It helps in developing scalable and independent services. It also used in cloud-based applications.
IoT (Internet of Things) Applications: Handles real-time data streaming from IoT devices. It is suitable for smart home automation and sensor-based systems.
Serverless Computing: Works well with AWS Lambda, Azure Functions, and Google Cloud Functions. Runs lightweight serverless functions efficiently.
Single-Page Applications (SPAs): It used in React, Angular, and Vue.js applications. It manages API requests efficiently in the backend.
Data-Intensive Applications: It used for big data processing and real-time analytics. It works well with NoSQL databases like MongoDB and Firebase.

Applications of NodeJS

Web Development: NodeJS powers backend services for web applications, handling HTTP requests and managing APIs efficiently.

Real-Time Applications: Used in chat applications, online gaming, and live streaming services due to its event-driven, non-blocking architecture.
Server-Side Applications: Enables full-stack JavaScript development, handling database operations, authentication, and server logic.
Microservices Architecture: Helps build scalable, independent microservices for modern web applications.
API Development: Ideal for creating RESTful and GraphQL APIs that interact with databases and client applications.
IoT Applications: NodeJS efficiently handles real-time data processing for IoT devices like sensors and smart home systems.

Limitations of NodeJS

Security Risks – Being open-source and widely used, NodeJS applications are prone to security vulnerabilities like Cross-Site Scripting (XSS) and SQL Injection if not handled properly.

Single-Threaded Limitations: While the event loop manages concurrency efficiently, CPU-intensive tasks can block the thread, affecting performance.
Performance Issues with Heavy Computation: NodeJS is not ideal for CPU-bound tasks like machine learning or video processing, as it lacks multi-threading for heavy computations.
Callback Hell: Older asynchronous code heavily relied on nested callbacks, making it difficult to read and maintain, though Promises and Async/Await help mitigate this.
Weak Type Checking: Since NodeJS runs JavaScript, dynamic typing can lead to runtime errors and unpredictable behavior without strict type enforcement.

Conclusion

NodeJS is a powerful runtime environment that extends JavaScript beyond the browser, enabling fast, scalable, and non-blocking server-side applications. With its event-driven architecture, V8 engine, and rich NPM ecosystem, it is widely used for web development, APIs, real-time applications, and microservices. While it excels in handling I/O-intensive tasks, it may not be ideal for CPU-heavy computations.