Interview Questions

Node.js Interview Questions and Answers for Beginners

Node.js is a server-side technology that is popular with millions of developers worldwide. You have to be proficient in to become the ideal back-end or full stack developer. It is one of the most rewarding web development tools to learn, not only because of the good salary but also the fast and continued growth of job postings requiring knowledge of the technology.
In case you are planning to attend Node.js interviews in the near future, we are here to help you with a list of Top Node.js interview questions and answers that you must prepare in 2020.

1. What Is Node.js?

Node.js is an open-source, cross-platform, JavaScript runtime environment that executes JavaScript code outside a web browser. Node.js is server-side scripting based on Google’s V8 JavaScript engine. It is used to build scalable programs, especially web applications that are computationally simple but are frequently accessed.
You can use Node.js in developing I/O intensive web applications like video streaming sites. You can also use it for developing: Real-time web applications, Network applications, General-purpose applications, and Distributed systems.

2. Why do we use Node.js?

Node.js makes building scalable network programs easy. Some of its advantages include:

FastNode.js is built on Google Chrome’s V8 JavaScript Engine which makes its library very fast in code execution
AsynchronousNode.js based server never waits for an API to return data thus making it asynchronous
ScalableIt is highly scalable because of its event mechanism which helps the server to respond in a non-blocking way
Open SourceNode.js has an extensive open source community which has contributed in producing some excellent modules to add additional capabilities to Node.js applications
No BufferingNode.js applications simply output the data in chunks and never buffer any data

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

TypeProgramming LanguageInterpreter and environment for JavaScript
UtilityUsed for any client-side activity for a web applicationUsed for accessing or performing any non-blocking operation of any operating system
Running EngineSpider monkey (FireFox), JavaScript Core (Safari), V8 (Google Chrome), etc.V8 (Google Chrome)

4. Why Node.js is single threaded?

Node.js uses a single threaded model in order to support async processing. With async processing, an application can perform better and is more scalable under web loads. Thus, Node.js makes use of a single-threaded model approach rather than typical thread-based implementation.

5. How does Node.js works?

Node.js is a virtual machine that uses JavaScript as its scripting language and runs on a v8 environment. It works on a single-threaded event loop and a non-blocking I/O which provides high rate as it can handle a higher number of concurrent requests. Also, by making use of the ‘HTTP’ module, Node.js can run on any stand-alone web server.

6. Where Node.js can be used?

Node.js can be used to develop:

  • Real-Time Web Applications
  • Network Applications
  • Distributed Systems
  • General Purpose Applications

7. How many types of API functions are there in Node.js?

There are two types of API functions in Node.js:

  • Asynchronous, non-blocking functions
  • Synchronous, blocking functions

8. What is the difference between Asynchronous and Non-blocking?

Asynchronous means not synchronous. Using these we can make asynchronous HTTP requests that do not wait for the server to respond. These functions continue to respond to the request for which it has already received the server response.

Non-blocking functions are used in regards with I/O operations. They immediately respond with whatever data is available and keeps on running as per the requests. In case, any answer couldn’t be retrieved then the API returns immediately with an error.

9. What is package.json?

The package.json file in Node.js is the heart of the entire application. It is basically the manifest file that contains the metadata of the project where we define the properties of a package.

  "name": "techbowl",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "jest --watchAll --verbose",
    "start": "node index.js"
  "engines": {
    "node": "v11.2.0"
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "@hapi/joi": "^17.1.0",
    "bcrypt": "^4.0.1",
    "compression": "^1.7.4",
    "config": "^3.3.0",
    "express": "^4.17.1",
    "express-async-errors": "^3.1.1",
    "fawn": "^2.1.5",
    "helmet": "^3.22.0",
    "jsonwebtoken": "^8.5.1",
    "lodash": "^4.17.15",
    "mongoose": "^5.0.2",
    "winston": "^3.2.1",
    "winston-mongodb": "^3.0.2"
  "devDependencies": {
    "jest": "^25.1.0",
    "supertest": "^4.0.2"

10. What are the functionalities of NPM in Node.js?

NPM (Node Package Manager) provides two functionalities:

  • An online repository for Node.js packages.
  • Command-line utility for installing packages, version management and dependency management of Node.js packages.

11. What is the difference between Node.js and Ajax?

Node.js and Ajax (Asynchronous JavaScript and XML) are the advanced implementations of JavaScript. They all serve entirely different purposes.

Ajax is primarily designed for dynamically updating a particular section of a page’s content, without having to update the entire page.

Node.js is used for developing client-server applications.

12. What is the difference between AngularJS and Node.js?

Angular.JS is a web application development framework, while Node.js is a runtime system.

13. What is an Event loop in Node.js and how does it work?

An event loop in Node.js handles all the asynchronous callbacks in an application. It is one of the most important aspects of Node.js and the reason behind Node.js have non-blocking I/O. Since Node.js is an event-driven language, you can easily attach a listener to an event and then when the event occurs the callback will be executed by the specific listener.

node.js event loop
Image Source:

Whenever functions like setTimeout, http.get, and fs.readFile are called, Node.js executed the event loop and then proceeds with the further code without waiting for the output. Once the entire operation is finished, Node.js receives the output and then executes the callback function. This is why all the callback functions are placed in a queue in a loop. Once the response is received, they are executed one by one.

14. Explain REPL in the context of Node.js.

REPL in Node.js stands for Read, Eval, Print, and Loop. It represents a computer environment such as a window console or Unix/Linux shell where any command can be entered and then the system can respond with an output. Node.js comes bundled with a REPL environment by default. REPL can perform the below-listed tasks:

  • Read: Reads the user’s input, parses it into JavaScript data-structure and then stores it in the memory.
  • Eval: Receives and evaluates the data structure.
  • Print: Prints the final result.
  • Loop: Loops the provided command until CTRL+C is pressed twice.

Since every question has more than one answer, feel free to personalize your answers as much as possible, especially when you have work experience to relate the answers to. Good Luck!

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