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Top Interview Questions on Node.js Development You Must Know About In 2021

Node.js is one of the most popularly used server-side platforms in recent years. According to a survey by Statista, Node.js is used by around 51.4% of respondents in the year 2020. Nowadays, the majority of the business owners opt for a digital platform to grow their business and Node.js is the most popular technology, people demand it a lot. By seeing the popularity of Node.js, more and more techies are now planning to become Node.js developers.

If you are one such techie who is trying to be a part of a Node.js development company, having knowledge of the technology and being prepared to answer the interview questions is very important.

In this blog, we will discuss some of the most asked Node.js development interview questions as per the experience level of the interviewee.

Node.js Interview Question & Answers As Per Different Categories

Beginner Level Node.js Interview Questions

1. What is Node.js?

Node.js is a popular open-source, cross-platform environment. It is a library that enables the Node.js developers to run web apps outside the client’s browser. With the help of Node.js, one can create a server-side web app for the clients. Node.js also enables the use of I/O intensive web apps as similar to using video streaming sites. Besides this, Node.js is a technology that is a perfect solution for data-intensive apps as it uses an event-driven model.

2. Why use Node.js?

Node.js is a technology that app development companies use to create scalable network programs easily. Some of the advantages of using this JavaScript runtime environment are -

  • Offers data type and unified programming language.

  • Fast

  • Asynchronous

  • Great Concurrency

  • Doesn’t get Blocks

3. What are the key features of Node.js?

Some of the most critical features of Node.js are -

  • Single-Threaded but Scalable

  • Quick Code Execution

  • No Buffering

  • MIT License

  • Event-driven

  • Asynchronous APIs

4. How does Node.js work?

When a web server uses Node.js, there is a workflow that is followed. It is as follows -

  • The clients send a request to the webserver to start the interaction with the web apps. This type of request can be blocking or non-blocking -

  • Querying for Data

  • Updating Data

  • Deleting Data

  • All these incoming requests are retrieved by Node.js and are added in the Event Queue.

  • Then the requests are passed one-by-one from the Event Loop. Here the requests are scanned and checked whether they are simple or need any external resources.

5. What is event-driven programming?

Event-driven is nothing but a programming approach that is used by events to trigger different functions. Here the event can be anything like clicking a button on the mouse or typing a key. Besides this, event-driven programming has a call-back function that is registered whenever any event is triggered.

6. What do you mean by I/O?

The I/O term is used to describe an operation, device, or program that can transfer data. Every transfer is made through a medium, which can be a network, a physical device, or files within a system.

7. State the API functions in Node.js

The two important types of API function in Node.js are -

  • Synchronous, blocking functions

  • Asynchronous, non-blocking functions

8. Explain the modules of Node.js

In Node.js, modules are like JavaScript libraries. It can be used in Node.js apps to include the functions. require() function is used to add a module in the Node.js application. Some of the most used modules to provide the basic functionalities are -

  • HTTP

  • util

  • fs

  • stream

  • url

  • Query

9. Why do developers prefer Node.js over other backend technologies?

The reasons why app developers prefer Node.js are -

  • Node.js is perfect for creating real-time web apps and is data-intensive.

  • It is very fast.

  • Offers better synchronization of codebase between client and server-side.

  • Node.js is an easy language for beginners to create a web application.

Intermediate Level Node.js Interview Questions

1. What command can one use to import external libraries in Node.js?

When it comes to importing external libraries, the Node.js app development companies use the “require” command. For instance, “var http=require(“HTTP”).”

This command enables the loading of the HTTP library.

2. What do you mean by package.json file in Node.js?

The package.json is a very important file in Node.js. It is called the heart of this technology. It holds the metadata for the Node.js project.

The Node.js developer can find the package.json in the root directory of the Node.js module or app.

npm init is the command used to create a project using the package.json file.

3. What is an EventEmitter?

EventEmitter is nothing but a class that carries the objects that can emit the events. When an object of the EventEmitter throws an event then all these functions are called upon synchronously.

4. What is an Event Loop?

Event Loop is the most essential feature in the Node.js development world. In Node.js, the Event Loop handles asynchronous callbacks. This is known as the foundation of the non-blocking I/O.

5. What is the Express.js package, and how can you create a simple app using it?

In Node.js, Express is a very flexible web app framework that offers various features to create mobile and web applications. To create a simple Express.js application, the Node.js developers need to follow the following steps -

  • In the Express.js package, the request object states the HTTP request. It has properties like parameters, HTTP headers, query-string, and more.

  • While on the other hand, when we talk about response objects, it represents the HTTP response that is sent by the Express application when an HTTP request is received.

6. Create a simple Node.js program that returns Hello World

To create a simple Node.js program, the developer must follow these steps -

  • First of all, one must import the HTTP module.

  • Then by using the createServer function, one can request and respond as parameters.

  • After that, type “Hello World.”

  • Now, set the port to 8080 for the server to listen to it and then assign the IP address.

Advanced Level Node.js Interview Questions

1. Explain the REPL concept in Node.js

Read Eval Print Loop (REPL) is a computer environment that is similar to Linux/Unix or Windows. REPL is a system that responds with an output to the command entered. Some of the tasks performed by it are:

  • Read

  • Eval

  • Print

  • Loop

2. Explain the fork() and spawn() methods

The fork() is a special case of the spawn() method. It is used to create a new V8 engine instance. Multiple workers run on a single Node.js codebase.

While on the other hand, spawn() is the method that launches a new process by using the set of available commands. The spawn() method is not able to create a V8 instance.

3. List out the flags considered in the read/write operations

The list of Node.js flags that are used to read/write the operations are -

  • r (This flag is used for opening a file to read it)

  • r+ (This flag is used for opening a file to read and write it. Here a problem might if the file doesn’t exist)

  • w (This flag is used for opening a file to write it)

  • w+ (This flag is used for opening a file to read and write it. Here the file is created but if not there.)

  • a (This flag is used for opening a file to append it )

  • a+ (This flag is used for opening a file to read and append it)

4. What does the buffer class mean in Node.js?

Buffer class is all about storing the raw data. It is quite similar to an array of integers. It is also used for JavaScript.

5. Explain the term piping

Piping is nothing but a mechanism that is used by the Node.js development service providers to connect the output of a stream with another. Piping is also used to retrieve data and pass it.

6. What is the callback hell term in Node.js?

Callback hell means Pyramid of Doom. It is the result of unreadable, intensively nested, and unmanageable callbacks. If the implementation of the asynchronous logic is not proper then it can cause callback hell.


With the use of Node.js technology, the developers can use JavaScript language for server-side scripting. By running the scripts on the server-side, the Node.js developers can create dynamic content for web pages. Because of the work process of Node.js and its popularity, more and more techies are turning towards Node.js development. To get a job as a Node.js developer they will have to be well prepared to answer the interview questions similar to the ones listed in this blog.

Source: Medium

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