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30+ NodeJS Interview Questions And Answers

Node.js is a powerful JavaScript runtime environment that allows developers to create server-side applications using JavaScript. It's known for its non-blocking I/O model and event-driven architecture, making it ideal for building scalable and efficient network applications such as web servers, real-time communication platforms, and microservices. Node.js is also a popular choice due to the vast ecosystem of packages available through npm, which can speed up the development process significantly. In interviewing candidates for Node.js roles, it's crucial to assess their understanding of core concepts, best practices, and their ability to solve problems using Node.js. Below are Node.js interview questions tailored for both beginners and advanced developers.


Most asked NodeJS interview questions



What is Node.js and why is it used?

Node.js is a server-side platform built on the V8 JavaScript engine. It's used for building fast and scalable network applications.


How does Node.js handle asynchronous operations?

Node.js uses callbacks, promises, and async/await patterns for handling asynchronous operations.


Can you show an example of a simple server created with Node.js?

const http = require('http');
http.createServer((req, res) => {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello World\n');
console.log('Server running at http://localhost:3000/');

This code snippet creates a basic HTTP server that responds with 'Hello World' for every request.


Explain 'require' in Node.js.

'require' is a built-in function to include external modules in a Node.js file.


What does 'console.log(' output?

It outputs the process ID of the Node.js process.


What is the event loop in Node.js?

The event loop is a mechanism that handles asynchronous callbacks in Node.js.


What are error-first callbacks?

Error-first callbacks are the standard in Node.js for passing errors and data. The first argument is an error object, with the actual data as the second argument.


What is the use of the 'fs' module in Node.js?

The 'fs' module is used to interact with the file system, allowing reading and writing of files.


How can you avoid callback hell?

To avoid callback hell, you can use promises, async/await, or modularize callbacks.


What is a Buffer in Node.js?

A Buffer is a chunk of memory allocated outside of the V8 JavaScript engine that can store binary data.


How do you serve static files in a Node.js application?

Use the Express framework and its 'static' middleware, or manually set up file serving using the 'fs' and 'http' modules.


How do you create a RESTful API in Node.js?

You create a RESTful API by setting up HTTP routes that handle requests according to REST principles, typically using Express.js.


What is middleware in the context of Node.js and Express?

Middleware is a function that has access to the request object, response object, and the 'next' function in the application's request-response cycle.


What is a package.json file?

A package.json file holds metadata about the project and includes a list of dependencies required by the application.


Can Node.js be used for front-end and back-end development?

Node.js is primarily used for server-side (back-end) development, but when paired with tools like webpack or Browserify, it can also be involved in front-end build processes.

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Explain how Node.js handles child processes.

Node.js can create child processes using the 'child_process' module, to execute other scripts or programs.

const { exec } = require('child_process');
exec('node -v', (error, stdout, stderr) => {
  if (error) {
    console.error(`exec error: ${error}`);
  console.log(`Node.js version: ${stdout}`);


What is the purpose of module.exports?

The module.exports is used to expose functions, objects, or variables for use in other files.


How does Node.js support multi-threading? Provide an example.

Node.js uses worker threads to achieve multi-threading. Below is an example of creating a worker thread.

const { Worker, isMainThread, parentPort } = require('worker_threads');
if (isMainThread) {
  const worker = new Worker(__filename);
  worker.once('message', (message) => {
} else {
  parentPort.postMessage('Hello from the worker thread');


Discuss streams in Node.js and their types.

Streams in Node.js are objects that let you read data from a source or write data to a destination continuously. The four types are Readable, Writable, Duplex, and Transform streams.


How do you ensure that a function does not block the event loop? Provide code.

To avoid blocking the event loop, you can use asynchronous functions or create child processes. An example using async/await:

async function fetchData() {
  let data = await someAsyncOperation();
  return data;


What are Microservices in Node.js?

Microservices in Node.js are small, independent services that work together in an application, each running in its own process and communicating via APIs.


How does the cluster module work, and when would you use it?

The cluster module allows you to create child processes that all share server ports, enhancing performance by load balancing incoming connections across multiple worker processes.


What is the Node.js event emitter and give an example of how it is used?

The event emitter is a module in Node.js that allows objects to publish events to be consumed by other objects. See the example below:

const EventEmitter = require('events');
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();
myEmitter.on('event', () => {
  console.log('an event occurred!');


Why might you use the 'net' module in Node.js?

The 'net' module is used for creating TCP or IPC servers and clients.


Discuss garbage collection in Node.js. How can you manually trigger it?

Garbage collection in Node.js is a memory management process for deallocating objects that are no longer needed. To trigger it manually, use '--expose-gc' flag and 'global.gc()'.


How do you debug a Node.js application?

You can debug Node.js applications using the built-in 'debugger' keyword, Node.js Inspector or debugging tools in IDEs such as VSCode.


Explain how you can handle uncaught exceptions in Node.js.

Uncaught exceptions can be handled with the 'process.on('uncaughtException', handler)' listener, which catches exceptions not caught by any try/catch.


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

process.nextTick() defers the execution of a callback until the next iteration of the event loop, which is before any I/O events. setImmediate() executes a callback after the current event loop cycle and after any I/O events.


Discuss how you can monitor the performance of a Node.js application.

You can monitor performance using tools like PM2, Node.js Application Metrics or the built-in 'perf_hooks' module.


What are V8 native bindings in Node.js and why are they useful?

V8 native bindings allow Node.js to call C++ functions from JavaScript code. They are useful for performing tasks that are computationally intensive or not possible in pure JavaScript.


NodeJS Interview Tips

Understand the Fundamentals

  • It's crucial to have a solid grasp of the basics when answering tough interview questions. Develop a clear understanding of Node.js event-driven architecture, non-blocking I/O, modules, events, and error handling. Being able to explain concepts like the event loop, callbacks, asynchronous programming, and JavaScript runtime will show your proficiency. Additionally, know how to set up a simple server, manage packages with npm, and use Node.js core modules like 'http', 'fs', 'path', and 'events'. Refresh your knowledge on newer features like async/await, and practice building simple applications to get comfortable with Node.js mechanics. Demonstrating this foundational knowledge confidently will make it easier to tackle complex questions that may arise.

Explain with Examples

  • Using specific examples can significantly improve the way you answer difficult questions. When discussing a particular concept, try to illustrate it with a relevant code sample or compare it to real-world scenarios. For example, if the question is related to the event loop, you could describe the loop as the heart of Node.js that pumps events to the application, just like the heart pumps blood to the body. You can also show a simple code snippet that demonstrates the event loop in action. When asked about error handling, provide an example that showcases proper use of try/catch or error-first callbacks. Concrete examples not only show your practical experience but also make your explanation more tangible and easier to grasp for the interviewer.

Clarify Before Responding

  • Before responding to a difficult question, make sure you fully understand what is being asked. If the question is vague or complex, don't hesitate to ask for clarification or to restate the question in your own words to confirm your understanding. This helps to provide a more precise answer and shows the interviewer that you are thorough and attentive to detail. If you're asked about a specific method or technique in Node.js you are not familiar with, you could explain a similar concept you know and express a willingness to learn. Remember, it's okay to admit not knowing something as long as you show a proactive attitude towards learning it in the future.

Structure Your Answers

  • When tackling tough interview questions, organizing your thoughts can be highly beneficial. Start with a brief overview, then delve into specifics, and end with a conclusion or summary. This structure ensures that you don't stray from the main topic and that your answer is comprehensive. For instance, if asked about scaling a Node.js application, begin with what scaling means in the context of web applications. Then discuss different strategies like cloning, creating microservices, or using a load balancer. Conclude by mentioning tools that facilitate scaling in Node.js. A structured response like this demonstrates not only your knowledge but also your ability to communicate ideas clearly and systematically.

Bring Up Personal Experience

  • Personal stories and experiences can make your answers to complex questions stand out. When discussing advanced Node.js topics, relate them to specific projects or tasks you've previously worked on. If asked about performance tuning, you can mention a time when you optimized an application by using Node.js performance tools or refactoring inefficient code. Sharing challenges you've encountered and how you addressed them helps convey your practical expertise and problem-solving skills. Furthermore, mentioning outcomes, such as improved response times or resource usage, quantifies your achievements and provides solid evidence of your capabilities as a Node.js developer.


How much does IT cost to hire a NodeJS developer?

The cost to hire a NodeJS developer varies depending on their experience and location, but with FireHire, rates start from $45/hour. Read more: How much does IT cost to hire a NodeJS developer?

What is the hourly rate for NodeJS?

Hourly rates can range broadly, but at FireHire we provide competitive rates beginning at $45/hour for skilled NodeJS developers. Read more: What is the hourly rate for NodeJS?

How do I find NodeJS developers?

Connect with FireHire to quickly access a pool of senior, pre-vetted NodeJS developers, tailored to meet the specific needs of your project. Read more: How do I find NodeJS developers?

Why using FireHire for hiring NodeJS developers is the best choice?

FireHire stands out for its quick delivery of senior, pre-vetted talents, comprehensive tech coverage, risk-free hiring process, and an efficient, cost-effective strategy to augment your team with top NodeJS professionals.

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