NodeJs Interview Questions

Here are some Node.js interview questions along with concise answers which is asking frequently:

1. What is Node.js?

• Node.js is a JavaScript runtime built on Chrome’s V8 JavaScript engine for executing JavaScript on the server-side.

2. How is Node.js different from JavaScript in the browser?

• Node.js is designed for server-side development and provides access to file systems, network sockets, and other server-specific APIs, while browser JavaScript is sandboxed and runs in a web browser.

3. What is npm and what is its purpose?

• npm (Node Package Manager) is the package manager for Node.js. It is used to install, manage, and share packages (libraries) for Node.js.

4. What is a callback in Node.js?

• A callback is a function passed as an argument to another function, which is then executed when a specific event occurs, such as the completion of an asynchronous operation.

5. What is the event loop in Node.js?

• The event loop is a core concept in Node.js that allows non-blocking, asynchronous execution of code. It handles I/O operations, callbacks, and events.

6. Explain the purpose of the require function in Node.js.

• The require function is used to load and include external modules in Node.js applications.

7. How can you create a simple HTTP server in Node.js?

You can create an HTTP server in Node.js using the built-in http module. Here’s an example:

const http = require('http');
const server = http.createServer((req, res) => {
  res.end('Hello, World!');
});
server.listen(3000);

8. What is the purpose of the module.exports object in Node.js?

• module.exports is used to export a single object, function, or value as the public interface of a module.

9. How do you handle asynchronous operations in Node.js?

• Asynchronous operations in Node.js can be handled using callbacks, Promises, async/await, or libraries like async.js.

10. What is the purpose of the fs module in Node.js?
– The fs (file system) module in Node.js is used for file-related operations, such as reading, writing, and manipulating files.

11. How can you handle errors in Node.js?
– Errors in Node.js can be handled using try-catch blocks for synchronous code and callback error parameters or Promise catch for asynchronous code.

12. What is the process object in Node.js, and how is it used?
– The process object provides information and control over the Node.js process. It can be used to access environment variables, exit the process, and more.

13. What is the purpose of the os module in Node.js?
– The os module provides information about the operating system, including details about the CPU, memory, and network interfaces.

14. Explain what middleware is in the context of Express.js.
– Middleware functions in Express.js are functions that have access to the request and response objects. They can be used for tasks like logging, authentication, and error handling.

15. How do you handle routing in Express.js?
– Routing in Express.js is handled using route handlers defined with app.get(), app.post(), etc., specifying the route path and callback functions.

16. What is JWT authentication, and how can you implement it in Node.js?
– JWT (JSON Web Token) is a method for securely transmitting information between parties. In Node.js, you can implement JWT authentication using libraries like jsonwebtoken.

17. What is clustering in Node.js, and why is it useful?
– Clustering in Node.js is the technique of creating multiple child processes to take advantage of multi-core CPUs, improving application performance and scalability.

18. Explain the difference between callbacks and Promises.
– Callbacks are functions that are passed as arguments and executed upon the completion of an asynchronous operation. Promises are a more structured way to handle asynchronous operations and provide better error handling and readability.

19. How can you handle cross-origin requests (CORS) in Node.js?
– CORS can be handled in Node.js using middleware like cors to set appropriate HTTP headers to allow or deny cross-origin requests.

20. What is streaming in Node.js, and how is it useful?
– Streaming in Node.js allows you to process data in chunks, making it efficient for handling large amounts of data. It’s commonly used for file I/O and network operations.

21. What is the purpose of the child_process module in Node.js?
– The child_process module allows you to create and manage child processes, execute shell commands, and communicate with them.

22. How can you read and parse JSON files in Node.js?
– You can use the fs module to read JSON files and JSON.parse() to parse them into JavaScript objects.

23. Explain what the net module in Node.js is used for.
– The net module is used for creating both TCP and UNIX socket servers and clients in Node.js.

24. What is the role of the url module in Node.js?
– The url module provides utilities for parsing and formatting URLs. It’s used for working with URL-related operations in Node.js.

25. How can you handle environment variables in Node.js?
– You can access environment variables using process.env.VARIABLE_NAME in Node.js.

26. Explain how to use the async/await syntax in Node.js.
– async/await is used to simplify working with Promises in Node.js. You mark a function as async and use await inside it to wait for Promise resolution.

27. What is the purpose of the crypto module in Node.js?
– The crypto module provides cryptographic functionality, including encryption, decryption, hashing, and secure random number generation.

28. What is a WebSocket, and how can you implement WebSocket communication in Node.js?
– WebSockets provide full-duplex communication channels over a single TCP connection. In Node.js, you can implement WebSocket communication using libraries like ws.

29. How can you perform unit testing in Node.js?
– You can perform unit testing in Node.js using testing frameworks like Mocha, Jest, or Jasmine along with assertion libraries like Chai.

30. What is the “event” module in Node.js, and how is it used?
– The “event” module is used for creating and handling custom events in Node.js. It provides an EventEmitter class to work with events.

31. How can you handle file uploads in Node.js?
– File uploads in Node.js can be handled using middleware like multer or by parsing the req object directly for multipart/form-data requests.

32. What is GraphQL, and how can you implement a GraphQL server in Node.js?
– GraphQL is a query language for APIs. You can implement a GraphQL server in Node.js using libraries like `apollo-server

orexpress-graphql`.

33. How do you implement sessions in Express.js?
– Sessions in Express.js can be implemented using middleware like express-session to store session data on the server and associate it with a unique session ID.

34. Explain the difference between a callback and a promise.
– A callback is a function passed as an argument and executed upon the completion of an asynchronous operation. A promise represents a value that may be available in the future, allowing you to attach handlers for success and error.

35. What is the purpose of the Buffer class in Node.js?
– The Buffer class in Node.js is used to work with binary data directly. It’s particularly useful for I/O operations and handling binary data.

36. How can you handle authentication in Express.js?
– Authentication in Express.js can be handled using middleware like Passport.js, which provides various authentication strategies such as local, OAuth, and JWT.

37. What is the “util” module in Node.js, and how is it used?
– The “util” module provides utility functions in Node.js. It’s often used for debugging and error handling. For example, you can use util.promisify to convert callback-based functions into Promises.

38. What is the purpose of the “assert” module in Node.js?
– The “assert” module is used for writing assertions to verify that code behaves as expected. It’s commonly used in testing.

39. How can you securely store sensitive information like API keys in Node.js?
– Sensitive information can be securely stored in environment variables or using a configuration management tool like dotenv.

40. What is serverless computing, and how does it relate to Node.js?
– Serverless computing is a cloud computing model where you don’t manage servers. Node.js is commonly used for building serverless functions using platforms like AWS Lambda and Azure Functions.

41. How can you implement caching in a Node.js application?
– Caching can be implemented using in-memory stores like Redis or by utilizing HTTP caching headers.

42. What is the “stream” module in Node.js, and how is it useful?
– The “stream” module allows you to read or write data continuously in chunks, making it efficient for handling large datasets and I/O operations.

43. How do you implement server-side rendering (SSR) in a Node.js application?
– SSR can be implemented using frameworks like Next.js or custom Express.js middleware to render HTML on the server and send it to the client.

44. Explain the role of the “cluster” module in Node.js.
– The “cluster” module allows you to create multiple child processes to take advantage of multi-core CPUs, improving application performance and concurrency.

45. What is the purpose of the “zlib” module in Node.js?
– The “zlib” module provides compression and decompression functionality in Node.js, which is useful for optimizing data transfer.

46. How can you handle global variables in Node.js?
– Global variables in Node.js can be declared using global.variableName. However, it’s recommended to avoid excessive use of global variables for better code maintainability.

47. What are the differences between synchronous and asynchronous programming in Node.js?
– Synchronous programming blocks the execution until a task is completed, while asynchronous programming allows other tasks to continue without waiting.

48. How can you handle concurrent requests in Node.js?
– Concurrent requests can be handled using non-blocking asynchronous code, clustering, or load balancing techniques.

49. Explain how to use the “querystring” module in Node.js.
– The “querystring” module is used to parse and stringify query strings in URLs. It provides methods like parse() and stringify().

50. How do you debug Node.js applications?
– Node.js applications can be debugged using built-in debugging tools, such as node inspect, and by using external debuggers like Visual Studio Code with breakpoints and console logging.

These questions and answers cover a wide range of Node.js topics that you may encounter during interviews. Be sure to study and practice thoroughly to demonstrate your expertise in Node.js.