NodeJS Interview Questions

NodeJS Interview Questions​


This is a comprehensive guide on NodeJS developer interview questions. It has three sets of crucial NodeJS interview questions and answers: Beginners, Intermediate and Advanced.

With the help of our sure-fire NodeJS interview preparation guide, you can ace your upcoming interview and land your dream position as a NodeJS developer.

Introduction - NodeJS Interview Questions and Answers

NodeJS is the most popular asynchronous back-end javascript runtime environment that runs javascript engines and executes its codes. It’s designed to rapidly build scalable network applications.

Because of its rapid development, single-threaded event loop architecture and many other features are preferred among top companies. Hence no matter if you are a developer or a talent acquisition team we have gathered NodeJS interview questions that will help.

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NodeJS Interview Questions and Answers For Beginners

With practice, you will be able to respond to basic NodeJS interview questions with ease as a developer.

We have gathered some challenging NodeJS Developer interview questions for you in this part. You can get assistance from this section with these precise types of intermediate NodeJS interview questions you might face while looking for work.

1. Explain NodeJS Process Mode

The nodejs application code runs in a single thread and the nodejs run in a single process hence it requires very few resources compared to other runtime environments.

Once the users arrive on your web app, they are handled by a single thread and the I/O or the longer tasks will be performed asynchronously for a request. This means the single thread can move on to the next request without waiting for the existing request to complete. And when the async I/O completes the work, it sends a request for further response.

2. What is URL Module in NodeJS?

The URL module makes an URL readable by splitting it into parts. By using require() to include the module and parsing the address with the url.parse() method, it returns a URL object with each part of the address as URL.

* URL Module in Node.js
const url = require(‘url’);
const adr =
const q = url.parse(adr,
console.log(; //
console.log(q.pathname); // “/default.htm”
console.log(; // “?year=2022&month=april”
const qdata = q.query; // {
year: 2022, month: ‘april’ }
console.log(qdata.month); // “april”

3. How to Manage Packages in NodeJS?

The packages in NodejS can be managed by a number of package installers and their configuration files accordingly. Most of those use yarn or npm, and these provide all the Javascript libraries that target controlling environment-specific configurations.

We use packages such as package.json to maintain the version of libs being installed and package-lock.json to avoid any hassles of porting the app to different environments.

4. What is BigInt Data Type in NodeJS?

The BigInt is a bigint primitive created by attaching n to the end of an integer, or by just calling the BigInt() function and giving it an integer or string value.

* BigInt Data Type
const maxSafeInteger = 99n; //
This is a BigInt
const num2 = BigInt(’99’); //
This is equivalent const num3 = BigInt(99); //Also works
typeof 1n === ‘bigint’ // true
typeof BigInt(‘1’) === ‘bigint’ // true

5. How does Control flow Control Function Calls?

Control flow controls functions calls in 4 steps:

  • Control order of execution
  • Collect data
  • Limit concurrency
  • Call the following steps in the program
  • 6. Why use promises instead of callbacks?

    By using promises, you get an object whose actions can be decided after the async task is completed. This facilitates manageable codes and lets developers avoid the tedious callback steps.

    7. How to create a simple server in NodeJS that returns Hello.

    var http = require(“http”);
    http.createServer(function (request, response) {
    response.writeHead(200, {‘Content-Type’: ‘text/plain’});

    8. What are the two arguments that async.queue takes as input?

  • Task function
  • Concurrency value
  • Intermediate NodeJS Questions and Answers

    With practice, you will be able to respond to basic NodeJS interview questions with ease as a developer.

    We have gathered some challenging NodeJS interview questions for you in this part. You can get assistance from this section with these precise types of intermediate NodeJS interview questions you might face while looking for work.

    1. What is Undefined and Null Data Type in NodeJS

    When we assign a null value to a variable, then the value of that variable becomes null, whereas when a variable is defined without assigning a value, then it will automatically take undefined as a value.

    * NULL and UNDEFINED Data Type
    let a;
    console.log(a); // undefined
    let b = null;
    console.log(b); // null

    2. Explain event loop in NodeJS

    So when an I/O or an async function needs to be executed, the main thread sends it to another thread, which lets v8 keep executing the main code.

    Event loops have various phases with particular tasks like timers, pending callbacks, idle or prepared callbacks, poll, check callbacks, and close callbacks with various FIFO queues.

    Additionally, it checks for async I/O and timers between iterations and cleanly terminates if none are found.

    3. How to avoid callback hell using async await?

    Because of promises, async-await makes asynchronous code look like synchronized code. However, the async await returns functions that return promises.

    * Async Await
    const getrandomnumber = function(){
      return new Promise((resolve, reject)=>{
      setTimeout(() => {
      resolve(Math.floor(Math.random() * 20));
      }, 1000);
    const addRandomNumber = async function(){
      const sum = await getrandomnumber() + await getrandomnumber();

    4. Explain NodeJS streams

    Streams are the instances of an EventEmitter which is used to stream data in NodeJS. These are used to handle and manipulate large streaming files over the web. They rely on buffers for temporary storage.

    Types of streams:
    Writable: streams on which data can be written are writable streams.
    Readable: streams from which the data can be read are known as readable streams.
    Duplex: streams that are both writable and readable are known as duplex streams.
    Transform: duplex streams that can transform the writable and readable data are known as transform streams.

    5. How do process.nextTick() and setlmmediate() differ?

    process.nextTick(): It adds the callback function to the start of the next event queue. However, process.nextTick() is called for the first time at the start of the program before the event loop is processed.

    setlmmediate(): When the current event loop finishes It is used as a function. it’s the callback function placed in the check phase of the next queue event.

    * setImmediate() and process.nextTick()
    setImmediate(() => {
      console.log(“1st Immediate”);
    setImmediate(() => {
      console.log(“2nd Immediate”);
    process.nextTick(() => {
      console.log(“1st Process”);
    process.nextTick(() => {
      console.log(“2nd Process”);
    // First event queue ends here
    console.log(“Program Started”);
    // Output
    Program Started
    1st Process
    2nd Process
    1st Immediate
    2nd Immediate

    Advanced NodeJS developer Interview Questions

    1. How to manage callback hell using Async.js

    Async is a powerful npm module which manages asynchronous behavior of javascript. It works with both NodeJS and javascript written for browsers.

    It provides powerful utilities to work with the asynchronous process under different use cases.

    npm install –save async

    2. Explain WASI

    Web assembly provides the implementation of a Web assembly system interface specs through WASI API. It’s implemented in NodeJS using the WASI class.

    It was introduced to use the underlying OS via a collection of POSIX functions therefore it allowed apps to use resources efficiently and features that require system-level access.

    2. How can you make a post request?

    Using this code we can make a post request.
    * POST Request
    const request = require(“request”);“http://localhost:3000/action”, { form: { key: “value” } },
      function (error, response, body) {
      if (!error && response.statusCode === 200) {

    1. How to resolve unhandled exception in NodeJS

    The unhandled exception can be caught at the process level by attaching a handler for the uncaughtException event.
    process.on(‘uncaughtException’, function(err) {
      console.log(‘Caught exception: ‘ + err);

    Here the process is a global object which gives the information of the current process. This process is a listen-to function that listens to the events such as


    2. How to perform get request using axios?

    The following code can be used to perform a get request using axios.

    * Get Request using Axios
    const express = require(“express”);
    const app = express();
    const axios = require(“axios”);
    app.get(“/async”, async (req, res) => {
      try {
      const response = await /ul>axios.get(“”);
        } catch (err) {
        res.status(500).json({ message: err });
      app.listen(3000, function () {
        console.log(`App listening at http://localhost:3000/`);


    Whether you’re a developer getting ready for an interview or a hiring manager trying to find the ideal candidate, we believe these NodeJS interview questions and answers will be a tremendous help to you during the process.

    Keep in mind that technical proficiency is only one aspect of the hiring process. Both prior experience and soft skills are essential if you want to be hired for a high-paid web development position.

    Keep in mind that many of the NodeJS interview questions are open-ended. Not just the answer you memorized, but also your reasoning will interest the interviewer. Always be prepared to address any follow-up inquiries about how you came to your conclusion. Describe the way you think.

    Good Luck! Regarding your future NodeJS interview. You can browse through our listings for NodeJS developer jobs here.