Node.js Answers

Basic Node.js Answers

#	Question	Answer	Examples
1	What is Node.js?	A JavaScript runtime environment built on Chrome's V8 JavaScript engine	Allows running JavaScript code outside of a web browser
2	What is the purpose of Node.js?	Building server-side applications, network tools, command-line tools	Creating web servers, APIs, real-time applications, microservices
3	What is NPM?	Node Package Manager; the default package manager for Node.js	Installing, managing, and sharing Node.js packages (libraries)
4	How do you install a package using NPM?	Using npm install	npm install express
5	What is the package.json file?	A manifest file for a Node.js project, containing metadata and dependencies	Defines project dependencies, scripts, version
6	What is a module in Node.js?	A JavaScript file containing code that can be imported and exported	fs, http, path are built-in modules
7	How do you import a module?	Using the require() function	const fs = require('fs');, const myModule = require('./my-module');
8	How do you export a module?	Using module.exports or exports	module.exports = { myFunction: ... };, exports.myVar = ...;
9	What is Express.js?	A popular minimal and flexible Node.js web application framework	const express = require('express'); const app = express();
10	What is the Event Loop?	The core mechanism in Node.js that handles asynchronous operations	Manages callbacks, timers, I/O operations, etc.
11	What is asynchronous programming in Node.js?	Writing code that performs operations without blocking the main thread	Using callbacks, Promises, or async/await
12	What is a callback function?	A function passed as an argument to another function to be executed later	fs.readFile('file.txt', (err, data) => { ... });
13	What is the purpose of the process object?	Provides information about and control over the current Node.js process	process.env, process.argv, process.exit()
14	What is the fs module?	Provides functions for interacting with the file system	fs.readFile(), fs.writeFile(), fs.mkdir()
15	What is the http module?	Provides functionality for creating HTTP servers and clients	http.createServer((req, res) => { ... });

Intermediate Node.js Answers

#	Question	Answer	Examples
1	What is middleware in Express.js?	Functions that have access to the request object (req), response object (res), and the next middleware function in the application's request-response cycle	app.use((req, res, next) => { console.log('Request received'); next(); });
2	How do you handle routing in Express.js?	Using app.get(), app.post(), app.put(), app.delete(), etc.	app.get('/', (req, res) => { res.send('Home'); });
3	What are route parameters?	Placeholders in a route path that capture values	app.get('/users/:id', (req, res) => { res.send(req.params.id); });
4	What are query parameters?	Key-value pairs appended to the URL after a ?	app.get('/search', (req, res) => { res.send(req.query.q); });
5	What is a Promise?	An object representing the eventual completion (or failure) of an asynchronous operation	new Promise((resolve, reject) => { ... }).then(result => ...).catch(error => ...);
6	What is async/await?	Syntax sugar over Promises, making asynchronous code look and feel more synchronous	async function fetchData() { const response = await fetch('/api'); ... }
7	What is the EventEmitter class?	A base class for objects that can emit and handle events	const EventEmitter = require('events'); const myEmitter = new EventEmitter(); myEmitter.on('event', () => { ... });
8	What are Streams?	A way to handle data in chunks, rather than loading the entire data into memory	fs.createReadStream('file.txt').pipe(fs.createWriteStream('new.txt'));
9	Explain the concept of error handling in Node.js.	Using try...catch blocks (for synchronous code), .catch() (for Promises), error handling middleware	try { ... } catch (err) { ... }, promise.catch(err), app.use((err, req, res, next) => { ... });
10	What are environment variables?	Variables that store configuration information specific to the deployment environment	process.env.PORT, process.env.DB_HOST
11	What is nodemon?	A utility that monitors changes in the source code and automatically restarts the Node.js app	npm install --save-dev nodemon, then nodemon server.js
12	How do you manage dependencies?	Using the package.json file and npm install	npm install express lodash
13	What is the difference between require() and import?	require() is CommonJS (Node.js default); import is ES Modules (modern standard)	const express = require('express'); vs import express from 'express';
14	What is CORS (Cross-Origin Resource Sharing)?	A mechanism that allows a web page to request resources from a different domain (origin)	Using cors middleware in Express: app.use(cors());
15	What are common HTTP methods?	GET, POST, PUT, DELETE, PATCH	GET for fetching, POST for creating, PUT for updating, DELETE for removing.

Advanced Node.js Answers

#	Question	Answer	Examples
1	Explain the Event Loop in more detail.	Phases: Timers, Pending Callbacks, Idle/Prepare, Poll, Check, Close Callbacks	Understanding how Node.js handles asynchronous operations and manages the event queue.
2	What is the cluster module?	Allows creating multiple Node.js processes that share a single server port, utilizing multi-core CPUs	cluster.isMaster, cluster.isWorker, cluster.fork()
3	What is the purpose of a microservices architecture?	Breaking down a monolithic application into smaller, independent services	Scalability, resilience, maintainability, independent deployment.
4	What is an ORM (Object-Relational Mapper)?	N/ODM (Object-Document Mapper); Examples: Sequelize, Mongoose (for MongoDB)	const User = mongoose.model('User', new Schema({...}));
5	What are Worker Threads?	Allows running JavaScript code in separate threads for CPU-intensive tasks without blocking the main event loop	const worker = new Worker('./worker.js');
6	What is the concept of dependency injection?	A design pattern where dependencies are provided to a component rather than being created internally	Using constructor parameters, setter methods, or interfaces to inject dependencies.
7	How do you handle testing in Node.js?	Using frameworks like Jest, Mocha, Chai, Supertest	Unit tests, integration tests, end-to-end tests.
8	What is the purpose of error handling middleware in Express.js?	A special middleware function with four arguments ((err, req, res, next)) to catch errors	app.use((err, req, res, next) => { ... });
9	What is rate limiting?	Restricting the number of requests a client can make to an API within a specific time frame	Using middleware libraries like express-rate-limit to prevent abuse.
10	What is input validation?	Ensuring incoming data meets specific format and type requirements	Using libraries like Joi, Zod, express-validator
11	What is the concept of caching in Node.js?	Storing frequently accessed data in a faster store (e.g., Redis, Memcached) to improve performance	Using libraries like node-cache or integrating with Redis.
12	What is the purpose of WebSockets?	Enables real-time, bidirectional communication between client and server over a single connection	Real-time chat applications, live updates (e.g., using Socket.IO).
13	What is the concept of GraphQL?	A query language for APIs that allows clients to request exactly the data they need	Using Apollo Server, Express-GraphQL
14	What is a message queue?	A system for asynchronous communication between application components (e.g., RabbitMQ, Kafka)	Using libraries like bull, amqplib
15	How do you handle authentication and authorization?	Verifying a user's identity (authentication) and determining what they are allowed to do (authorization)	Using JWT (JSON Web Tokens), OAuth, session-based authentication.