Are you preparing for a Node.js interview and feeling overwhelmed by the vast amount of information out there? Look no further! We’ve compiled a list of the top 25 Node.js interview questions to help you ace your upcoming interview. Let’s dive in!

1. What is Node.js?

Node.js is an open-source server environment that uses JavaScript to create fast and easily accessible web software. It can run on various platforms, including Windows, Linux, and macOS.

2. What are the key benefits of Node.js?

  • Speed: Node.js is built on Google Chrome’s V8 JavaScript engine, making it incredibly fast.
  • Non-blocking: Node.js doesn’t block while working and outputs data in chunks.
  • Asynchronous: It’s ready to handle the next request without waiting for an API to return data.

3. Is Node.js single-threaded? If yes, then why?

Node.js is single-threaded in the sense that it executes one function at a time. However, it can use multiple threads internally for optimal performance, making it a multi-threaded server environment.

4. What types of applications can you build using Node.js?

You can build a wide range of applications with Node.js, including streaming apps, chat applications, IoT solutions, microservices, collaboration tools, and more.

5. How do you read the content of a file in Node.js?

Node.js provides the fs (file-system) module for interacting with system files. You can use the readFile method to read the contents of a file asynchronously. Here’s an example:

var fs = require('fs');

fs.readFile('DATA', 'utf8', function(err, contents) {

console.log('after calling readFile');

For synchronous reading, you can use the readFileSync method.

6. Discuss the streams in Node.js? What are the different types of streams?

Streams in Node.js allow continuous reading and writing of data from source to destination. There are four types of streams:

  • Readable: Promotes reading operations.
  • Writable: Promotes writing operations.
  • Duplex: Combines both readable and writable.
  • Transform: Performs computation based on available input.

7. What is a closure?

A closure is a function that is retained in another scope, allowing access to variables in the outer scope.

8. Does Node.js use Zlib? If yes, then why?

Yes, Node.js uses Zlib, a cross-platform data compression library, to handle data compression. You can use the node-zlib package to work with Zlib in Node.js.

9. Discuss the globals in Node.js.

Globals in Node.js include Global, Process, and Buffer. They provide various functionalities and act as a namespace object, offer information about the application, and handle binary data, respectively.

10. Differentiate between Node.js and Ajax.

Node.js is used for developing client-server applications, while Ajax is typically used to update specific sections of a web page’s content without refreshing the entire page.

11. What is Modulus in Node.js?

Modules in Node.js are reusable blocks of code used for maintainability, reusability, and namespacing. Modules are introduced in ES6 and play a crucial role in structuring Node.js applications.

12. What is an event loop, and how does it work?

An event loop manages all callbacks in a Node.js application. It enables non-blocking I/O by executing callbacks when specific events occur, making Node.js highly efficient and scalable.

13. What is callback hell?

Callback hell, also known as the Pyramid of Doom, occurs when multiple nested callbacks become unreadable and challenging to manage. It often results from improper implementation of asynchronous logic.

14. What are the types of API functions in Node.js?

Node.js has two main types of API functions: blocking and non-blocking. Blocking functions execute synchronously and block other code until I/O events complete. Non-blocking functions execute asynchronously and allow multiple I/O calls without waiting for each to finish.

15. What is Chaining in Node.js?

Chaining in Node.js refers to connecting the output of one stream to the input of another, creating a chain of multiple stream operations.

16. Explain the Exit codes in Node.js and name some examples.

Exit codes in Node.js are used to terminate a Node process. Examples include fatal errors, uncaught exceptions, internal JavaScript evaluation failures, and more.

17. What is the procedure to handle child threads in Node.js?

Node.js is primarily single-threaded, but you can use the spawn() method for specific asynchronous I/O tasks that run in the background without interfering with the main event loop.

18. Differentiate between readFile and createReadStream in Node.js.

readFile loads the entire file into memory before providing it to the client, while createReadStream reads and provides the file in smaller pieces, resulting in faster data delivery.

19. How to update a new version of NPM in Node.js?

You can update NPM by running the following command:

$ sudo npm install npm -g

20. How to prevent/fix callback hell?

To prevent or fix callback hell:

  • Handle every error properly.
  • Keep your code shallow by modularizing it.
  • Use Promises, Generators, or Async functions to improve code readability.

These strategies help make asynchronous code more manageable.

21. What are the different timing features of Node.js?

Node.js provides a Timers module that contains various functions for executing code after a specified period. Some timing features include:

  • setTimeout/clearTimeout: Schedules code execution after a set number of milliseconds.
  • setInterval/clearInterval: Repeatedly executes code at specified intervals.
  • setImmediate/clearImmediate: Executes code at the end of the current event loop cycle.
  • process.nextTick: Schedules a callback function to run in the next iteration of the event loop.

22. What is the usage of the buffer class in Node.js?

The Buffer class in Node.js is used for storing raw data similar to an array of integers. It corresponds to a memory allocation outside the V8 heap. Buffers are essential for handling binary data, as pure JavaScript is not well-suited for binary data manipulation.

23. What is the role of REPL in Node.js?

REPL stands for Read, Eval, Print, Loop. It’s a shell in Node.js that allows you to execute JavaScript code interactively. It’s invaluable for testing, debugging, and experimenting with JavaScript code on the fly.

24. What is libuv in Node.js?

libuv is a cross-platform I/O abstraction library used by Node.js to provide asynchronous I/O based on the event loop. It’s written in C and is released under the MIT License. libuv supports various operating systems and is crucial for Node.js’s asynchronous operations.

25. How do you handle child threads in Node.js?

Node.js is primarily single-threaded and doesn’t expose traditional child threads. However, you can make use of the spawn() method for specific asynchronous I/O tasks that run in the background without interfering with the main event loop. This allows you to manage parallel operations efficiently.

n this comprehensive guide, we’ve delved into the top 25 Node.js interview questions to help you prepare for your upcoming Node.js interview. Node.js is a powerful runtime environment that has gained immense popularity for its ability to build scalable and high-performance applications.

From understanding the basics of Node.js to diving into asynchronous programming and handling various aspects of the Node.js ecosystem, these questions cover a wide range of topics you may encounter during your interview.

As you prepare for your interview, remember that it’s not just about memorizing answers but also grasping the underlying concepts. Node.js is a dynamic and evolving technology, and interviewers often seek candidates who can demonstrate a deep understanding of its principles.

Take the time to practice coding exercises, experiment with real-world projects, and stay updated with the latest developments in the Node.js community. This hands-on experience will not only boost your confidence but also help you stand out as a well-rounded Node.js developer.

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