Node.Js Developer Interview Questions and Answers for Freshers Part 1

Node.Js Developer Interview Questions:

Basic Questions

1. What is Node.js?
   • Answer: Node.js is a JavaScript runtime built on Chrome’s V8 JavaScript engine that allows you to run JavaScript on the server-side.
2. What is the difference between Node.js and JavaScript?
   • Answer: JavaScript is a programming language that runs in web browsers, whereas Node.js is a runtime environment that allows JavaScript to be executed on the server-side.
3. What are the main features of Node.js?
   • Answer: Non-blocking I/O, event-driven architecture, single-threaded but scalable, V8 JavaScript engine, and a large package ecosystem with npm.
4. What is npm?
   • Answer: npm (Node Package Manager) is a package manager for Node.js, which allows developers to share and reuse code modules.
5. How do you install a package using npm?
   • Answer: You can install a package using the command npm install <package-name>.

Intermediate Questions

6. What is the purpose of the package.json file?
   • Answer: The package.json file holds various metadata relevant to the project, such as project name, version, dependencies, scripts, and author details.
7. How do you initialize a Node.js project?
   • Answer: You can initialize a Node.js project using npm init or npm init -y for default settings.
8. What is a callback function in Node.js?
   • Answer: A callback function is a function passed into another function as an argument, which is then invoked inside the outer function to complete some kind of routine or action.
9. What is the event loop in Node.js?
   • Answer: The event loop is a single-threaded mechanism in Node.js that handles asynchronous operations. It processes operations asynchronously and executes callbacks when they are complete.
10. Explain the concept of middleware in Express.js.
    • Answer: Middleware functions in Express.js are functions that have access to the request object (req), the response object (res), and the next middleware function in the application’s request-response cycle.

Advanced Questions

11. What are streams in Node.js?
    • Answer: Streams are objects that enable reading data from a source or writing data to a destination in a continuous manner. Examples include readable streams, writable streams, duplex streams, and transform streams.
12. How does Node.js handle concurrency?
    • Answer: Node.js handles concurrency using an event-driven, non-blocking I/O model, along with the event loop, which allows it to manage multiple operations concurrently without multiple threads.
13. What is the difference between process.nextTick() and setImmediate()?
    • Answer: process.nextTick() schedules a callback function to be invoked in the same phase of the event loop, while setImmediate() schedules a callback to be executed in the next iteration of the event loop.
14. What is the purpose of the cluster module in Node.js?
    • Answer: The cluster module allows you to create child processes that share the same server ports, enabling load balancing and better utilization of multi-core systems.
15. What is the role of the V8 engine in Node.js?
    • Answer: The V8 engine is the JavaScript engine developed by Google that executes JavaScript code. In Node.js, V8 compiles JavaScript directly to native machine code, allowing for fast execution.

Practical Coding Questions

16. How do you create a basic HTTP server in Node.js?
    • Answer:
    const http = require('http');

    const server = http.createServer((req, res) => {
    res.statusCode = 200;
    res.setHeader(‘Content-Type’, ‘text/plain’);
    res.end(‘Hello, World!\n’);
    });

    server.listen(3000, ‘127.0.0.1’, () => {
    console.log(‘Server running at http://127.0.0.1:3000/’);
    });

17. How do you read a file in Node.js?
    • Answer:
    const fs = require('fs');

    fs.readFile(‘example.txt’, ‘utf8’, (err, data) => {
    if (err) throw err;
    console.log(data);
    });

18. How do you handle errors in Node.js?
    • Answer: Errors can be handled using try-catch blocks for synchronous code and callback functions or Promises with .catch() for asynchronous code.
19. What is the difference between require and import?
    • Answer: require is used in CommonJS modules, and import is used in ES6 modules. require loads modules synchronously, while import supports asynchronous loading and is part of the standard JavaScript specification.
20. How do you create a route in Express.js?
    • Answer:
    const express = require('express');
const app = express();app.get(‘/’, (req, res) => {
    res.send(‘Hello, World!’);
    });

    app.listen(3000, () => {
    console.log(‘Server is running on port 3000’);
    });

Miscellaneous Questions

21. What is the purpose of the exports object in Node.js?
    • Answer: The exports object is used to export functions, objects, or primitive values from a module so they can be used in other modules using require.
22. What are Promises in Node.js?
    • Answer: Promises are objects that represent the eventual completion or failure of an asynchronous operation and its resulting value.
23. How do you handle asynchronous code in Node.js?
    • Answer: Asynchronous code can be handled using callbacks, Promises, or async/await syntax.
24. What is the purpose of the fs module in Node.js?
    • Answer: The fs (file system) module provides an API for interacting with the file system, allowing for reading, writing, updating, and deleting files.
25. What is a RESTful API?
    • Answer: A RESTful API is an API that adheres to the principles of Representational State Transfer (REST), which includes stateless communication, use of standard HTTP methods, and resource-based URIs.

Best Practices and Design Patterns

26. What is the single responsibility principle?
    • Answer: The single responsibility principle states that a module or class should have only one reason to change, meaning it should have only one job or responsibility.
27. How can you improve the performance of a Node.js application?
    • Answer: Performance can be improved by optimizing database queries, using caching, load balancing, minimizing middleware, and using efficient algorithms.
28. What is the purpose of middleware in Express.js?
    • Answer: Middleware functions are used to handle requests, modify responses, handle errors, and execute any code before the request reaches the route handler.
29. How do you handle environment variables in a Node.js application?
    • Answer: Environment variables can be managed using the process.env object or by using packages like dotenv to load variables from a .env file.
30. What are some common security practices for Node.js applications?
    • Answer: Common security practices include using HTTPS, validating input, sanitizing user data, avoiding eval statements, implementing authentication and authorization, and keeping dependencies up to date.

Debugging and Testing

31. How do you debug a Node.js application?
    • Answer: Debugging can be done using console logs, the Node.js built-in debugger, or using debugging tools like node-inspect, Chrome DevTools, or Visual Studio Code’s debugger.
32. What is Mocha in the context of Node.js?
    • Answer: Mocha is a test framework for Node.js that simplifies writing and running tests, supporting both synchronous and asynchronous testing.
33. How do you write a simple test using Mocha and Chai?
    • Answer:
    const chai = require('chai');
const expect = chai.expect;describe(‘Array’, function() {
    it(‘should return -1 when the value is not present’, function() {
    expect([1, 2, 3].indexOf(4)).to.equal(-1);
    });
    });

34. What is the difference between unit testing and integration testing?
    • Answer: Unit testing involves testing individual components or functions in isolation, whereas integration testing involves testing how different modules or components work together.
35. What is TDD (Test-Driven Development)?
    • Answer: TDD is a software development approach where tests are written before writing the actual code. The cycle involves writing a test, running it to see it fail, writing code to pass the test, and then refactoring the code.

Advanced Topics

36. What are WebSockets, and how are they used in Node.js?
    • Answer: WebSockets are a protocol for full-duplex communication channels over a single TCP connection, often used for real-time applications. In Node.js, they can be implemented using libraries like ws.
37. How do you handle file uploads in Node.js?
    • Answer: File uploads can be handled using middleware like multer in Express.js, which processes multipart/form-data forms.
38. What is the purpose of the process object in Node.js?
    • Answer: The process object provides information about the current Node.js process and allows interaction with the runtime environment, including reading environment variables, handling signals, and more.
39. How do you ensure data consistency in a distributed Node.js application?
    • Answer: Data consistency can be ensured by using transactions, distributed locks, consensus algorithms like Raft or Paxos, and databases that support eventual consistency.
40. What is the event emitter in Node.js?
    • Answer: The event emitter is a core module in Node.js that facilitates the creation of event-driven architectures by allowing objects to emit and listen for events.

Additional Knowledge

41. What is the purpose of the Buffer class in Node.js?
    • Answer: The Buffer class is used to handle binary data directly in Node.js, particularly for reading or writing binary data to/from files, network connections, or other I/O operations.
42. How do you handle exceptions in Node.js?
    • Answer: Exceptions in Node.js can be handled using try-catch blocks for synchronous code and using .catch() with Promises or async/await for asynchronous code.
43. What is the difference between path.join() and path.resolve() in Node.js?
    • Answer: path.join() joins path segments using the platform-specific separator, normalizing the resulting path. path.resolve() resolves a sequence of paths into an absolute path.
44. What is a microservice architecture?
    • Answer: Microservice architecture is a design approach where an application is composed of loosely coupled, independently deployable services, each serving a specific business function.
45. What is CORS, and how do you handle it in a Node.js application?
    • Answer: CORS (Cross-Origin Resource Sharing) is a mechanism that allows restricted resources on a web page to be requested from another domain. It can be handled in Node.js using the cors middleware.

Practical Implementation Questions

46. How do you create a RESTful API with Express.js?
    • Answer:
    const express = require('express');
const app = express();
app.use(express.json());let items = [];

    app.get(‘/items’, (req, res) => {
    res.json(items);
    });

    app.post(‘/items’, (req, res) => {
    const newItem = req.body;
    items.push(newItem);
    res.status(201).json(newItem);
    });

    app.listen(3000, () => {
    console.log(‘API is running on port 3000’);
    });

47. What is the async and await syntax in Node.js?
    • Answer: async and await are used to handle asynchronous code in a synchronous-like manner. async functions return a Promise, and await pauses the function execution until the Promise is resolved.
48. How do you use the dotenv package in Node.js?
    • Answer:
    // Install the package using: npm install dotenv
require('dotenv').config();const port = process.env.PORT || 3000;
    console.log(`Server is running on port ${port}`);

49. How do you connect to a MongoDB database using Mongoose?
    • Answer:
    const mongoose = require('mongoose');

    mongoose.connect(‘mongodb://localhost:27017/mydatabase’, { useNewUrlParser: true, useUnifiedTopology: true })
    .then(() => console.log(‘Connected to MongoDB’))
    .catch(err => console.error(‘Failed to connect to MongoDB’, err));

50. How do you handle session management in an Express.js application?
    • Answer:
    const express = require('express');
const session = require('express-session');const app = express();
    app.use(session({
    secret: ‘mysecretkey’,
    resave: false,
    saveUninitialized: true,
    cookie: { secure: false } // Set secure to true in production with HTTPS
    }));

    app.get(‘/’, (req, res) => {
    if (!req.session.views) {
    req.session.views = 1;
    } else {
    req.session.views++;
    }
    res.send(`Number of views: ${req.session.views}`);
    });

    app.listen(3000, () => {
    console.log(‘Server is running on port 3000’);
    });