Node.js Interview Questions to Ask a Candidate

Last updated on 05 May 202112 min

Anyone who has ever encountered the hiring process knows that it is a challenging thing. Despite the abundance of options, goals, and hiring objectives, you can't recognize the right specialist. What about the Node.js developers? However, according to the Stack Overflow Survey in 2020, Node.js is firmly in the lead, so Node.js developers are in demand.

most popular development technologies

Imagine a situation where you need a particular specialist. However, you do not know what questions you should ask a novice and experienced programmer at a technical interview to hire someone who can correctly solve complex problems. A technical discussion is one of the most critical stages, and business owners should take it as carefully as possible. We created interview questions on Node.js that will help you learn how to prepare for a Node.js interview by the business owner.

Therefore, we have divided the questions into three categories:

  1. Junior Node.js Interview Questions
  2. Senior Node.js Interview Questions
  3. Additional, non-tech questions for Node.js candidates

Junior Node.JS Interview Questions

This section contains Node.js interview questions for 1 year experienced. Naturally, beginners don't have significant experience. However, during the Node.js coding task, specialists should submit sample projects. Suppose beginners don't have enough knowledge of interacting with the team. In that case, these questions will help you understand their soft skills, understand the desire to learn, and improve themselves as specialists.

The questions for 1 year experienced Node.js developers are more theoretical than practical. However, novice specialists should know the basics. During the technical interview, they should give clear answers about how coding works with Node.js, its advantage over other technologies. They should understand technical but straightforward coding concepts such as event loop and event programming during interview questions on Node.js.

What is Node.js, and how does it works?

Node.js is an open-source JavaScript runtime based on Google Chrome's JavaScript V8 engine. Developers can indeed say that's neither a programming language nor a framework and will be correct. However, what’s it? Node.js is like JavaScript but with the extended traditional functions beyond the web browser. Node.js specialists use it to develop network applications independently and at scale.

How do you manage packages in your Node.js project?

Programmers can manage packages using NPM. It is a Node Package Manager, which is in the system by default. Developers use it to install and update JavaScript packages and modules. To maintain the libraries' versions, developers use package.json and package-lock.json to port this application to another environment.

What is a package.json file in Node.js?

Package.json is, you might say, the heart of the app. This manifest file includes various metadata associated with the project, including applications, modules, libraries, packages. A specialist during Node.js interview questions for 1 year experienced can tell you that package.json makes a program reproducible. There are two fields in the package.json file - package name and deals.

package.json file example

Why, in your opinion, was the V8 engine necessary?

A detailed response to this question may also cover some other relevant features of V8, such as the memory structure, functions of Garbage collector, and memory leaks and methods of addressing them. Someone can be confused by these questions for 1 year experienced. So, we decided to discuss the basics of V8 and it logically leads lead to the following question:

Why is Node.js single-threaded? There was the thread-based implementation of scaling via different frameworks. However, developers went further and created a new theory of doing async processing on a single thread over the previous type. It is an experiment in async processing.

async processing on a single thread

How does the Event loop work? We believe this is one of the most important interview questions on Node.js for beginners. An event loop is a framework that manages events by executing callback functions in a queue. It is responsible for its asynchronous and non-blocking I / O. It is important to know that an automatic flow is created in the event loop. It plans operations based on the specified conditions. There is only one thread, which is an event loop that determines which thread will execute callback functions at any given time.

node js event loop flow

What are the timing features of Node.js?There are four commonly used timing features of Node.js you can ask during Node.js interview questions:

  • setTimeout / clearTimeout - can be used to delay code execution
  • setInterval / clearInterval - can be used to execute a block of code continuously
  • process.nextTick - can be used to set code execution at the beginning of the next cycle of the event loop
  • setImmediate / clearImmediate - can be used to execute code at the very end of the event loop.

What is event-driven programming?

It is a popular approach, which uses events to trigger various functions. The event can be anything, for example, clicking of a mouse button. When the event happens, we have a callback process, which has registered with the element, following the "publish-subscribe" pattern. Thanks to this flexible approach, Node.js is more productive than other technologies.

What are the advantages of Node.js compared to other backend technologies?

Multitasking: enabled by an asynchronous, non-blocking model.

Fast transition: a developer who has ever worked with JavaScript will have no problems switching to backend Node.js development.

Flexibility and performance: easy castability and flexibility significantly improves the performance of sites and applications that perform real-time tasks (video streaming, chat, online games)

Possibility of a clear full-stack development: if your product is developed on the front with JavaScript and internal with the help of Node.js, you create a comfortable full-stack process.

Active support for well-known brands: Microsoft, PayPal, Amazon, Netflix, Uber, and LinkedIn create their products with Node.js.

With Node.js, you have a big chance to be a part of digital media trends with your new project.

What are the main API functions in Node.js?

Asynchronous or non-blocking: a function to control operations to increase the playback speed dramatically. Thanks to the non-blocking process, the programmer can perform several operations simultaneously without waiting for the server's response at each stage, increasing the speed.

Synchronous or Blocking: This feature allows threads to be queued. It creates a sequential operation one after the other for a multithreaded structure. We advise against using this feature for single-threaded tasks.

What is the difference between asynchronous and non-blocking modes?

The asynchronous mode is when we do not receive a response immediately. There is no dependence on the execution of the action. The server stores information and will accept confirmation only when an action is performed. We use this mode to improve efficiency and productivity in general.

The non-blocking mode does not stop or block any operations. In contrast to the asynchronous mode, we will receive the response immediately. If there is no data, then there will be an execution error.

Which frameworks are popular in Node.js?

Express: It's flexible and lightweight. It has distinctive features like basic routing, model-view-controller (MVC), middleware. The main priority of this framework is to increase performance.

Koa: It can be called an innovative next-generation framework. Express created it by removing middleware. The new framework has received additional functional settings.

Hapi: If you need a large commercial site, then the choice is just for this framework. It has a code reuse function and a high level of security.

Nest: If you want easy scalability and extensive support for JavaScript libraries, this is the best choice.

Adonis: This framework has its own Command Line Interface (CLI), is easy to use; yet another takes the Laravel approach.

Check our article on Node.js frameworks in comparison for a better understanding.

Senior Node.js Interview Questions

These are more technical Node.js interview questions and answers for experienced developers. Of course, these are complicated questions. Your employee is no longer a beginner but an experienced developer who knows the subtleties accurately identifies the system's advantages and disadvantages. In this section, not theoretical Node.js interview questions for experienced but practical issues related to coding and solving complex problems are already critical. By answering these interview questions on Node.js, you will have a complete picture of your employee and their appropriate experience for that level.

What disadvantages do you see in using Node.js?

The question indirectly touches on some other technologies such as C# and Java, for example. Besides, it covers some obsolete types of Node.js usage, such as relational databases. It is about responsiveness under intensive CPU computation. When you hire senior Node.js developers, candidates should see in what applications the effectiveness of Node.js is questionable and why this technology is not a silver bullet in each case.

However, when you hire senior Node.js developers as experts, they can already clearly name the following points and explain what solutions they propose to use:

Unstable API is due to frequent updates and a lack of backward compatibility. An experienced developer knows to change the code with a new version constantly.

Asynchrony sometimes causes callback nightmares and degrades the app performance. It is vital to avoid a situation where callbacks are nested several levels deep within other callbacks, making the code difficult to maintain.

Node.js doesn’t provide a full-fledged toolkit, so developers are forced to add additional libraries.

What is EventEmitter?

A Node.js class has objects that are capable of emitting events. During node.js interview questions for experienced, the programmer will reply that you can generate events by attaching named events caused by the object using the eventEmitter.on () function. When an object generates attached parts, they will be synchronous.

event emitter node js code example

What are the streams? How many are they?

Streams are like communication channels that read data from the source and sequentially transmit it to the destination.

There are four types of streams:

  • Readable: used for reading a large amount of data from a source;
  • Writeable: used for writing data to the destination;
  • Duplex: for reading and writing operations;
  • Transform: duplex stream used for data modification.

Streams allow Node.js to work with streaming data in, for example, live video streaming, like Instagram LIVE or Twitch. By the way, do you know how to make a video streaming website with great profit?

Why use WebSocket and Socket.IO for Node.js?

WebSocket is a protocol that is used to build streaming web applications and real-time communication applications. It enables fast two-way messaging between client and server and deploys real-time applications quickly and efficiently. It works effectively with Node.js, ensuring that real-time communication and data flow are hassle-free. Now you can quickly implement live chat applications with Node.js WebSockets.

What about Socket.IO? It is a JavaScript library based on WebSockets and other technologies. Unlike WebSockets, Socket.IO allows you to send messages to all connected clients. It isn't easy to use proxying and load balancers in WebSockets. Socket.IO supports these technologies out of the box. Socket.IO supports gradual degradation, supports automatic reconnection when the connection is broken and is also easier to use. It may seem like Socket.IO is the best tool for live communication. However, there are several situations where it is better to use WebSockets.

Node.js interview questions and answers for experienced must be prepared carefully. Developers know that threads process files sequentially without relying on memory. However, there are cases; the programmer will answer you during the Node.js interview questions for experienced when the file size is larger than the memory. What to do? There is only one way out - it is to use streams to read the file in bits and save space in memory. Then streams are very efficient when dealing with enormous amounts of data.

There are four types of streams in Node.js, which are:

  • Readable: Used to read large amount of data from source - fs.createReadStream()
  • Writeable: Used to write data to destination - fs.createWriteStream()
  • Duplex: Used for both read and write -net. Socket
  • Transform: A duplex stream used for data modification - zlib.createDeflate()

How to improve the performance of Node.js through clustering?

node js cluster manager

One of the critical Node.js interview questions and answers for experienced that you should ask. Node.js applications run on a single processor. What does it mean? They will not use multi-core systems by default. We use clustering to run multiple processes by instantiating an event loop. When we start using the cluster in a Node.js application behind the scenes, numerous Node.js processes are created. However, there is also a parent process called the cluster manager. It is responsible for monitoring the state of individual instances of your application.

What is REPL in Node.js?

In the context of Node.js, REPL means read, evaluate, print and loop. The REPL is a computing environment in which any command entered is met with a system's response. The REPL environment performs the following tasks by default:

Read: Reads the input and converts it to a JavaScript data structure, storing it in memory

Eval: It gets the data structure and evaluates it Print: gives the result

Loop: will repeat the given command until CTRL + C before you press it twice.

What is tracing?

This module enables you to use trace_events, which allows you to track information generated by V8, user-space code, and Node.js core on the central system. During the Node.js interview questions for experienced, the specialist will tell that the first task is to define the Node app pattern and perform system monitoring of the data. Tracing will give you an idea of performance and help you troubleshoot future memory problems.

What are the functions of middleware?

Middleware functions are needed to req (change request objects) and res (response objects). It creates a req-res loop. The parts work by providing access to req and res. Besides req and res, there is one more parameter: the following function -next (), which ensures that the request does not hang and time out.

What is libuv, and how does it works in a thread pool?

It is a multi-platform C library supporting asynchronous I / O-based operations such as file systems, networking, and concurrency. The libuv library processes the thread pool in Node.js.

modules dependent on libuv

What is WASI? Why should you use it?

A web assembly implements the WebAssembly system interface specification via the WASI API in node.js. The use of WASI was made to make better use of functions and resources that require system-level access.

What are child processes? What is the difference between Spawn and Fork?

Being single-threaded but scalable, Node.js allows developers to take advantage of multiple processes. Thus, a large workload is quite acceptable. When you hire senior Node.js developers, they can create and handle child processes in Node.js using the child process module. These processes interact with each other, which is why Node.js got its codename: node-to-node communication. How to create child processes? You can use Spawn () to execute system commands. Its peculiarity is that once it is launched, it does not execute additional code in the process. If you have a command inside another command, the fork () method is acceptable, which will start a new instance of the V8 engine.

Additional, non-tech questions for Node.js candidates

General Node.js interview questions and answers for experienced and junior specialists are an essential part. They reveal the essence of the candidates as experts and as people as well. It is crucial to correctly formulate abstract questions to understand their values, aspirations, and views. After all, productive cooperation directly depends on the links in the chain!

What previous experience do you have with Node.js?

This question is a test of integrity. A candidate with no actual practice in Node.js can hardly trick professional developers, and the ability to remember theoretical definitions should not be a ticket to the team. Simultaneously, this is not about performing tasks on the go with paper and pencil or in some online editor. It is always better to give some “homework” assignments to a candidate to show that experience matters.

What is, in your opinion, an ideal Node.js development workflow?

Candidates should describe their vision of the entire process, beginning with identifying the problem and up to the delivery of code to production. Team workflow is a necessary process to describe due to Node.js interview questions for experienced how to communicate with a remote team, solve conflicts, integrate different time zones, combine quick releases with developers' wishes, etc. It may not be a compulsory one in the list of Node.js interview questions since many senior developers write code. In general, understanding of a team workflow is expected from seniors.

Which Node.js framework do you personally prefer?

This specific question can say a lot about the actual cognitive distance between the candidate and the Node.js technology. Different tools aid the management of data between servers and applications in the realm of Node.js. The most popular one is Express.js, but the answers can differ when you hire senior Node.js developers. For instance, developers who prefer, for example, Hapi.js should defend their choice: whether this is about scalability, minimalism, or any other characteristic of the framework.

Do you interact with Node.js beyond work?

It is always helpful to know how deeply candidates are interested in the technology they are working with: which relevant news channels they monitor, which open-source projects Senior Node.js developers participate in, which thematic conferences they attend, etc. A broad beyond-work experience in Node.js can add extra points to any candidate.

What is your previous work experience?

The question might seem irrelevant, but this is far from the truth. This one can reveal more about a candidate than all previous Node.js interview questions together. It is important not to approach this topic superficially, just for the show. Knowing any relevant information about the candidate won’t hurt.

Do you have any questions to ask us right now?

It is an excellent move to make candidates re-evaluate their intention to work for the company when the interview is over. In case a candidate appears weak for the job position, the issue can help both the candidate and the interviewer make up for the discomfort of the inevitable refusal. Besides, a suggestion to ask the employer anything disposes to more sincere revelations from candidates.

How to prepare for Node.js interview - AnyforSoft advice

As a company with ten years of international experience, AnyforSoft knows that hiring developers for startups is hard enough. It is crucial to understand which candidate hides the real treasure and is not worth wasting your time. To not miss your person who will be able to work real miracles in the future, it is essential to follow specific hiring rules. How to prepare for Node.js interview if you are an employer?

An employer should approach node js interview questions and answers for experienced and beginners as straightforwardly as possible. At the first stage of your search for a developer, look at the portfolio of candidates. A candidate who does not show growth, and development does not deserve attention. It is essential to prepare in advance technical questions and answers for different levels. We understand that interview questions on node.js of specialists of different levels differ in complexity. Therefore, it is vital to divide the questions into three categories:

The additional questions will help check the software skills of potential employees, their English knowledge, their level of erudition and desire, and their ability to develop. In interview questions on node.js, it is essential to pay attention to how they interact with the team, their values, and their work attitude. Sometimes node.js interview specialists with 1-year experience have a great desire for growth and development is much more valuable than senior node js developers who are stuck in place and are focused exclusively on themselves.

When you hire senior Node.js developers or beginners, the main thing is an orientation towards knowledge, human values, and a desire for development. Two aspects that play an essential role in decision-making are technical and personal. If these two puzzles add to a single business values system ​​and requirements, this is an excellent start for collaboration.


It is possible to make the process of hiring Node.js specialists understandable and energy-free. That is why we have prepared Node.js interview questions and answers for experienced candidates and beginners to make an employer's life much easier. How to prepare for Node.js interviews with maximum benefits? In our article, you have the opportunity to see the questions for the junior and senior Node js developers to get acquainted with soft skills questions, which help to indicate the person. In this way, you are killing two birds with one stone by asking the right both sides questions.

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