Top 25 Node Js Interview Questions For Experienced professionals

 

The percentage of Node.js careers is increasing, which directly relates to the growing competitiveness. This requires the most thorough preparation possible. You may also refer to Node.js best practices for your practical understanding and this article for your theoretical one!

This blog of top Node Js interview questions has been carefully chosen to provide you with solutions to some of the most often asked Node JS interview questions. By following the advice meticulously, you may gain the strategic advantage necessary to nail your Nodejs interview. We have also tried to cover some interview questions on NodeJs for all those experienced developers out here reading this blog. 

​Preparing for a Node.js interview can involve several steps, and here are a few tips to help you prepare:

​

1. Know the basics of Node.js: You should have a solid understanding of the fundamental concepts of Node.js, including asynchronous programming, event-driven architecture, modules, and callbacks.

2. Understand JavaScript: Since Node.js is built on top of JavaScript, it's essential to have a strong grasp of JavaScript concepts and syntax, such as functions, data types, and object-oriented programming.

3. Familiarize yourself with popular Node.js libraries and frameworks: You should know about the most popular Node.js libraries and frameworks like Express, Koa, and Nest.js.

4. Practice coding: Spend some time practicing coding in Node.js, by working on small projects or taking online coding challenges. This will help you get comfortable with the language and develop your problem-solving skills.

5. Prepare for behavioral questions: Be ready to answer behavioral questions, as many interviewers will want to learn more about your experience, work style, and problem-solving approach.

6. Research the company and the position: Spend some time learning about the company you're interviewing with and the role you're applying for. This will help you tailor your responses to the interviewer's questions and demonstrate your interest in the position.

7. Be prepared for technical questions: The interviewer may ask you technical questions related to Node.js, including the architecture of a Node.js app, creating and using middleware, error handling, and debugging techniques.

Node.js is an incredibly robust framework built on Google Chrome’s JavaScript engine, which immediately converts JavaScript into native machine code. It is a small framework for developing server-side web-based apps that extends the JavaScript API to provide common server-side functionality. It is typically used for developing server software, and large-scale programs, particularly online streaming websites, single-page apps, and other online applications.

1. What is Node.js?

Node.js is a JavaScript runtime environment built with Chrome’s V8 JavaScript engine as a platform. It’s popular because it’s lightweight and efficient, due to its event-driven and non-blocking I/O model. Built with performance as its primary focus, Node.js processes the JavaScript code into the native machine code, which your computer can use to execute processes. 

Even though Node.js is based on Chrome’s V8 engine, it doesn’t run in the browser itself. During development, various features like file system API, HTTP library and OS utility methods were added to the engine, so Node.js could be executed as a program on a computer.

2. How are “Child Threads” handled in Node.js?

Primarily, Node.js is a single-thread process. It doesn’t expose any child threads and the modes of thread management to the developer. However, child threads may be generated in Node.js in various processes like asynchronous I/O. Although the child threads spawned through these processes run in the backdrop, they don’t block the main code or execute any application code. But if you require threading support in an application powered by Node.js, multiple tools are available for utilization.

3. Name any three features of Node.js?

Here is the list of important features of Node.JS

• No buffering: Node.js applications never buffer any data(ASCII). These applications simply output data in chunks.

• Extremely Fast: Node.js is built on Google Chrome’s Javascript V8 Engine so its library is very fast in code execution. As you are aware Javascript is used to built client side applications which is also built on V8 engine, so this makes Node JS applications faster.

• I/O is Asynchronous and Event Driven: All APIs of Node.js library are asynchronous i.e. non-blocking. So a Node.js based server never waits for an API to return data. The server moves to the next API after calling it and a notification mechanism of Events of Node.js helps the server to get a response from the previous API call. It is also a reason that makes it is very fast

• Highly Scalable: Node.js is highly scalable because event mechanism helps the server to respond in a non-blocking way.​

4. How does Node.js work?

A web server using Node.js typically has a workflow that is quite similar to the diagram illustrated below. Let’s explore this flow of operations in detail.

• Clients send requests to the webserver to interact with the web application. Requests can be non-blocking or blocking:

• Querying for data

• Deleting data 

• Updating the data

• Node.js retrieves the incoming requests and adds those to the Event Queue

• The requests are then passed one-by-one through the Event Loop. It checks if the requests are simple enough not to require any external resources

• The Event Loop processes simple requests (non-blocking operations), such as I/O Polling, and returns the responses to the corresponding clients

A single thread from the Thread Pool is assigned to a single complex request. This thread is responsible for completing a particular blocking request by accessing external resources, such as computation, database, file system, etc.

Once the task is carried out completely, the response is sent to the Event Loop that sends that response back to the client.

5. What is npm?

Npm or Node Package Manager is the default package manager for Node.js.It works as:

1. An online repository called as npm registry is used for the open-source Node.js projects.npm registry is a large database with around half a million packages. Developers can download from and publish packages to the npm registry.

2. Npm is also a  command-line utility for interacting with an online repository that helps in package installation, version management, and dependency management.

Few of the important  npm commands are:

• Any package can be installed  by running a simple command

“ npm install <name of the package> “.

This will install the module under the path, “./node_modules/”. Once installed the module could be used just like they were built-ins. Dependency management could also be done with npm. Our node project will have a package.json which will have all the dependencies needed for our project. If we perform “npm install” from project root all the dependencies listed in the package.json file will be installed.

• “npm init” Here package.json file is created that is where all dependencies are included.

• “npm update <package_name>”  where the specific package is updated with new features

• “npm uninstall <package_name>” where the specific package is uninstalled. It’s then removed from the “node_modules” folder.

• “npm list” is used to list all the packages installed.

• “npm help” is the built-in help command. To get help for a particular command, use

“npm <command> -h”

6. Which Types of Apps are Developed Using Nodejs?

Some of the most popular types of Node.js applications available in the market are – 

• Single-Page Applications: Node.js is used for creating single-page applications as it has the capability to handle heavy input/output workloads, asynchronous calls, and more. In addition to this, with the help of Node.js SPAs can have a seamless transition of data between the server and the view. 

• Real-time Collaboration Tools: Node.js is one of the most popular engines when it comes to creating real-time collaboration tools which include collaborative document editing tools, video & audio conferencing tools, and more. 

• Location-based Applications: The majority of the location-based applications in the market are created using Node.js. The reason behind it is that Node offers asynchronous programming and event-based architecture. 

• Real-time Applications: Creating real-time applications with Node is the best decision as it enables developers to create applications like instant messaging apps, internet relay chat, and more. 

• Streaming Applications: Streaming applications are created using Node.js where developers utilize stream API to easily handle real-time data streams and also synchronize data quickly between the client and the server.

7.  How Would You Define the Term I/O?

Any program, activity, or device that acts as a mediator to transfer data from one media to another is referred to as I/O- input-output. Every transfer is a result of one medium’s output and the input of another. For an input/output. In this way, a physical device, a network, or files within a system can be used as the medium between your internal system and external devices. And once this process is completed, it pushes the result to the event queue. Now what is the event queue you may ask? Well if JS is busy in some task then it will queue that event and once the  JS is available it will provoke the next event in the queue (or event queue).

8. What are some of the most commonly used libraries in Node.js?

There are two commonly used libraries in Node.js:

• ExpressJS - Express is a flexible Node.js web application framework that provides a wide set of features to develop web and mobile applications.

• Mongoose - Mongoose is also a Node.js web application framework that makes it easy to connect an application to a database.​

9. In the context of Node.js, what is REPL?

REPL is Read, Eval, Print and Loop. REPL is a computer environment (similar to a Windows console or Linux shell) where any entered command is met with a system-response output. The REPL environment is bundled with Node.js by default, and it performs the following tasks:

• Reads user inputs, converts them into JavaScript data-structures, and stores them.

• Evaluates data structures.

• Prints the final output

• Loops the provided command until CTRL + C is pressed two times.

10. What is the difference between asynchronous and non-blocking?

Asynchronous or non-synchronous means that we will not receive a response to a message immediately — there is no dependency or order of execution. The server stores information and acknowledges when the action is performed. This improves performance and efficiency.

Non-blocking operation does not stop or block any operations. The difference is that a non-blocking operation receives a response immediately with whatever data is available. If data is not available, it returns an error. It is mostly used with I/O.

11. What is a first class function in Javascript?

When functions can be treated like any other variable then those functions are first-class functions. There are many other programming languages, for example, scala, Haskell, etc which follow this including JS. Now because of this function can be passed as a param to another function(callback) or a function can return another function(higher-order function). map() and filter() are higher-order functions that are popularly used.

12. What is NodeJs and how it works?

Node.js is a virtual machine that uses JavaScript as its scripting language and runs Chrome’s V8 JavaScript engine. Basically, Node.js is based on an event-driven architecture where I/O runs asynchronously making it lightweight and efficient. It is being used in developing desktop applications as well with a popular framework called electron as it provides API to access OS-level features such as file system, network, etc.

13. How do you manage packages in your nodeJs project?

It can be managed by a number of package installers and their configuration file accordingly. Out of them mostly use npm or yarn. Both provide almost all libraries of javascript with extended features of controlling environment-specific configurations. To maintain versions of libs being installed in a project we use package.json and package-lock.json so that there is no issue in porting that app to a different environment.

14. How is Node.js better than other frameworks most popularly used?

• Node.js provides simplicity in development because of its non-blocking I/O and even-based model results in short response time and concurrent processing, unlike other frameworks where developers have to use thread management.

• It runs on a chrome v8 engine which is written in c++ and is highly performant with constant improvement.

• Also since we will use Javascript in both the frontend and backend the development will be much faster.

• And at last, there are ample libraries so that we don’t need to reinvent the wheel.

15. Explain the steps how “Control Flow” controls the functions calls?

• Control the order of execution

• Collect data

• Limit concurrency

• Call the following step in the program.

16. What are some commonly used timing features of Node.js?

• setTimeout/clearTimeout – This is used to implement delays in code execution.

• setInterval/clearInterval – This is used to run a code block multiple times.

• setImmediate/clearImmediate – Any function passed as the setImmediate() argument is a callback that's executed in the next iteration of the event loop.

• process.nextTick – Both setImmediate and process.nextTick appear to be doing the same thing; however, you may prefer one over the other depending on your callback’s urgency.

17. What are the advantages of using promises instead of callbacks?

The main advantage of using promise is you get an object to decide the action that needs to be taken after the async task completes. This gives more manageable code and avoids callback hell.

18. What is fork in node JS?

A fork in general is used to spawn child processes. In node it is used to create a new instance of v8 engine to run multiple workers to execute the code.

19. Why is Node.js single-threaded?

Node.js was created explicitly as an experiment in async processing. This was to try a new theory of doing async processing on a single thread over the existing thread-based implementation of scaling via different frameworks.

20. How do you create a simple server in Node.js that returns Hello World?

var http = require("http");

http.createServer(function (request, response) {

response.writeHead(200, {'Content-Type': 'text/plain'});

response.end('Hello World\n');

}).listen(3000);

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

There are two types of API functions:

• Asynchronous, non-blocking functions - mostly I/O operations which can be fork out of the main loop.

• Synchronous, blocking functions - mostly operations that influence the process running in the main loop.

22. What is REPL?

PL in Node.js stands for Read, Eval, Print, and Loop, which further means evaluating code on the go.

23. List down the two arguments that async.queue takes as input?

• Task Function

• Concurrency Value

24. What is the purpose of module.exports?

This is used to expose functions of a particular module or file to be used elsewhere in the project. This can be used to encapsulate all similar functions in a file which further improves the project structure.

For example, you have a file for all utils functions with util to get solutions in a different programming language of a problem statement.

const getSolutionInJavaScript = async ({

problem_id

}) => {

...

};

const getSolutionInPython = async ({

problem_id

}) => {

...

};

module.exports = { getSolutionInJavaScript, getSolutionInPython }

Thus using module.exports we can use these functions in some other file:

const { getSolutionInJavaScript, getSolutionInPython} = require("./utils")

25. What tools can be used to assure consistent code style?

ESLint can be used with any IDE to ensure a consistent coding style which further helps in maintaining the codebase.

Overall, preparation is the key to success in Node JS interview questions. By studying the language, practicing coding, and researching the company and the position, you can present yourself as a qualified candidate and increase your chances of landing the job.