Ace Your Node.js Interview: 40 Essential Questions and Answers for Success

1. What is Node.js?

Node.js is a JavaScript runtime built on Chrome’s V8 engine that allows JavaScript to be run on the server side. It is known for being event-driven, non-blocking, and well-suited for building scalable, high-performance web applications.

2. What is the difference between Node.js and JavaScript?

• JavaScript is a scripting language primarily used for client-side web development.
• Node.js is a runtime environment that allows JavaScript to run outside the browser, typically on servers.

3. Is Node.js single-threaded?

Yes, Node.js is single-threaded, meaning it uses a single thread to execute JavaScript code. However, it utilizes asynchronous, non-blocking operations to manage concurrency efficiently.

4. What kind of API function is supported by Node.js?

Node.js supports asynchronous, non-blocking APIs. It also provides synchronous APIs, but asynchronous functions are preferred for better performance.

5. What is a module in Node.js?

A module in Node.js is a reusable piece of code that can be included in other files using the require() function.

6. What is npm and its advantages?

npm (Node Package Manager) is a package manager for Node.js.
Advantages:

• Easy management of dependencies.
• Access to a large ecosystem of packages.
• Version control for dependencies.

7. What is middleware?

Middleware is a function that has access to the request and response objects in a Node.js application. It is often used in Express.js to perform operations such as logging, authentication, and error handling.

8. How does Node.js handle concurrency despite being single-threaded?

Node.js uses the event loop and asynchronous I/O operations to handle multiple tasks simultaneously without blocking the main thread.

9. What is control flow in Node.js?

Control flow refers to the order in which code is executed in Node.js, often involving callbacks, promises, or async/await to manage asynchronous operations.

10. What do you mean by the event loop in Node.js?

The event loop is a mechanism in Node.js that processes callbacks and handles asynchronous operations, ensuring non-blocking execution.

11. What are the main disadvantages of Node.js?

• Callback hell: Complex nested callbacks.
• Single-threaded: Poor performance for CPU-intensive tasks.
• Immaturity: Some packages in the npm registry may be immature or poorly maintained.

12. What is REPL in Node.js?

REPL stands for Read-Eval-Print Loop. It allows developers to interactively execute JavaScript code and see the output immediately.

13. How to import a module in Node.js?

Use the require() function:

const fs = require('fs');

14. What is the difference between Node.js and AJAX?

• Node.js: Runs JavaScript on the server.
• AJAX: A technique for making asynchronous HTTP requests from the browser.

15. What is package.json in Node.js?

package.json is a file that contains metadata about the project and lists its dependencies, scripts, and configuration.

16. What is the most popular Node.js framework used these days?

Express.js is the most popular Node.js framework for building web applications and APIs.

17. What are promises in Node.js?

A promise is an object that represents the eventual completion or failure of an asynchronous operation and provides methods like .then() and .catch().

18. What is event-driven programming in Node.js?

Event-driven programming involves triggering and listening for events, where certain actions are taken when an event occurs.

19. What is buffer in Node.js?

A buffer is a temporary storage area for binary data, used primarily for reading or manipulating streams.

20. What are streams in Node.js?

Streams are used to handle large volumes of data efficiently by breaking the data into chunks.
Types: Readable, Writable, Duplex, and Transform streams.

21. Explain crypto module in Node.js.

The crypto module provides cryptographic functions, such as encryption, decryption, and hashing.

22. What is callback hell?

Callback hell refers to a situation where multiple nested callbacks make the code difficult to read and maintain.

23. Explain the use of the timers module in Node.js.

The timers module provides functions like setTimeout(), setInterval(), and setImmediate() for scheduling code execution.

24. What is the difference between setImmediate() and process.nextTick() methods?

• setImmediate(): Executes code after the current event loop cycle.
• process.nextTick(): Executes code immediately after the current operation completes, before the event loop continues.

25. What is the difference between setTimeout() and setImmediate() methods?

• setTimeout(): Runs after a specified delay.
• setImmediate(): Runs after the current event loop cycle, without delay.

26. What is the difference between spawn() and fork() methods?

• spawn(): Creates a new process to execute a command.
• fork(): Creates a new Node.js process that shares some resources with the parent process.

27. Explain the use of the passport module in Node.js.

The passport module is used for authentication. It supports various strategies such as OAuth, JWT, and local authentication.

28. What is fork in Node.js?

The fork() method is used to create a child process that runs a separate Node.js instance.

29. What are the three methods to avoid callback hell?

1. Promises
2. Async/await
3. Modularization (splitting callbacks into separate functions)

30. What is body-parser in Node.js?

body-parser is middleware used to parse incoming request bodies in JSON, URL-encoded, or other formats.

31. What is CORS in Node.js?

CORS (Cross-Origin Resource Sharing) allows servers to specify who can access their resources by setting appropriate HTTP headers.

32. Explain the tls module in Node.js.

The tls module provides Transport Layer Security (TLS) and allows secure communication between clients and servers.

33. What is a cluster in Node.js?

A cluster allows Node.js to spawn multiple processes (workers) to handle tasks in parallel, utilizing multi-core CPUs.

34. How to manage sessions in Node.js?

Sessions are managed using packages like express-session and can be stored in memory, databases, or cookies.

35. Explain the types of streams in Node.js.

1. Readable: Data can be read (e.g., fs.createReadStream()).
2. Writable: Data can be written (e.g., fs.createWriteStream()).
3. Duplex: Both readable and writable.
4. Transform: Modifies data as it is read or written.

36. How can we implement authentication and authorization in Node.js?

Authentication can be implemented using passport or JWT. Authorization involves checking user roles and permissions before granting access to resources.

37. Explain the packages used for file uploading in Node.js.

Packages like multer and formidable are used to handle file uploads in Node.js.

38. How to handle database connections in Node.js?

Database connections can be managed using ORM libraries (like Sequelize for SQL) or drivers (like MongoDB native driver for NoSQL).

39. How to read command line arguments in Node.js?

Command line arguments can be accessed using process.argv:

console.log(process.argv);

40. What are child processes in Node.js?

Child processes allow Node.js to execute other programs or commands in separate processes, improving performance and scalability. They can be created using methods like spawn(), fork(), and exec().