Node.js Interview Questions and Answers: Hire The Best One With Our Advice

19 min read
Dec 28, 2020
Node.js Interview Questions and Answers: Hire The Best One With Our Advice
By
+1

Node.js is in popular demand and there is a shortage of developers that can handle this groundbreaking programming runtime. But if one were to sit across from you in an interview and you asked a few questions, are you prepared enough to be able to determine how skilled they are in the technicalities of Node.js?

The technical interview stage is the most important if you want to hire Node.js developers and it demands maximum readiness. It helps you to understand an applicant’s skills, experience, and vision for work. However, determining any of those begins by asking the right questions on programming with Node.js during the interview.

For example, during the interview, don’t expect Node.js backend developer who is applying for a senior programmer role to answer questions about the advantages of using Node.js. They could recite that offhand for you. However, to really interrogate the technical skills of a senior Node.js backend developer, ask them about the drawbacks of coding using Node.js and how they manage to overcome those drawbacks. You may know that Node.js developer average salary depends on the level of an engineer and such a question will help to evaluate this level.

How can you tell if a Node.js backend developer is as good as they claim during the coding interview? Showing you how is the purpose of this guide, which features both theoretical and applied Node.js interview questions and answers to help you prepare for a Node.js coding interview, as the employer.

General Node.js interview questions

The technical Node.js coding interview questions in this section are those that transcend any backend developer’s level of experience. Whether they are a beginner or a guru in Node.js programming, question them about work experience and past projects. These preparatory Node.js technical interview questions enable you to determine who is the right fit for the job.

Work Experience

Questions in this regard are an opportunity to understand the applicant’s technical experience programming with Node.js specifically. This stage should prepare you for the kind of Node.js technical interview questions that you would use as a follow-up. By then, you can tell if a person is less experienced than they claim to be.

A meme about work experience

When listening for answers to Node.js programming interview questions about work experience, focus on hands-on experience rather than theoretical education. That is, prioritize what a developer has actually done, rather than what they (say they) can do.

Industry Experience

Node.js programming interview questions in this regard are more specific than general work experience. Software development is not just about writing code; a backend developer also needs to gain some industry-specific knowledge that informs their Node.js programming inquiries and decisions and must demonstrate such when examined. Therefore, you want to examine Node.js backend developers to determine their preparation to navigate the terrain of your industry.

Health & WellnessSaaSLogistics
EntertainmentMarketingInternet of Things
ProCoders’ Industries

If you can’t readily find Node.js backend developers who have operated in your field, during the interview, question them to determine any transferable technical skills they might possess. That is, focus on skills they must have gained in another industry that can help them succeed in your own industry.

Certifications

On how to prepare for a Node.js interview or even programming interviews generally, most companies are moving beyond certificates to testing real skills. Yet, certifications still lend credence to a developer’s skills, especially when they come from reputable programs. So, remain prepared to request certificates from coding interview applicants, if they possess any, as they serve as additional proof of their backend development understanding particularly with Node.js.

 Mr. Bean meme

But more importantly than showcasing your technical qualifications, make provisions to ask them how each certificate program has enhanced their development as a backend developer who can code with Node.js specifically. That way, you can tell while interrogating them that those certificates are not just ‘paper’ qualifications but proof of real value garnered throughout their Node.js programming career.

Basic Node.js interview questions and answers for beginners

This section contains Node.js interview questions and answers for freshers. As a beginner, much is not expected of them. However, that should not be an excuse for the Node.js coding interview to not be thorough.

During the Node.js coding evaluation, be considerate that beginners don’t have significant experience. However, they must have carried out sample projects which they should be ready to present to you. Even without real-world experience working with a development team, that should pass for you as a sign of curiosity and aptness to learning, soft skills that every employer looks for in a beginner.

Developers' experience meme

Node.js interview questions for 1-year experienced developers are mostly theoretical rather than applied coding inquiries. Only examine the backend developer’s programming foundation in Node.js to determine that they understand the basics.

During the questioning, they provide answers that demonstrate familiarity with how coding with Node.js works, the applications it is used to build, its advantage over other similar technologies. Answering those questions properly signals that the Node.js developer is well-prepared for the interview and for the programming role itself.

They should also be able to break down simple but technical concepts in Node.js coding such as event loop and event-driven programming during the interview.

What is Node.js & how does it work?

Node.js is an open-source Javascript runtime based on Google Chrome’s Javascript V8 engine. It is neither a programming language nor a server-side framework. Javascript is the language and Node.js itself features frameworks such as Express and Adonis. Node.js is Javascript too and it extends the language’s traditional functions beyond the web browser to being able to develop network applications independently and at scale.

A joke about JavaScript

Basically, besides the Javascript code, it is composed of a single-thread event loop through which it handles requests by using callbacks to carry out queued functions.

What are the uses of Node.js?

It is a preferred solution for building complex single-page applications, streaming applications, as well as real-time chat and collaboration tools. Likewise, it is useful on the Internet of Things and for building microservices architecture.

How is front-end development different from back-end development? And in what category does Node.js fall?

Node.js is a unique platform. It is a backend development runtime that is based on Javascript, a language that is primarily used for front-end development.

It is used for back-end development though based on a primarily front-end application, javascript. It is inevitable that you discuss some Node.js backend developer interview questions. The table below highlights some factors that differentiate front-end development from back-end development.

Front-End DevelopmentBack-End Development
Manages the application client-sideManages the application server-side
Concerned with the features that the end-user of an application can see physically and likewise interact with: navigation, buttons, etcConcerned with the behind the scenes functionality of an application. Basically, how the application works, rather than how it looks
Additional skills required include UI/UX designAdditional skills required include database management
Work involves collaboration with designers, copywriters, etcWork involves database management and framework utilization
Common languages include HTML, CSS, and JavascriptCommon languages include PHP, Python, Java, and Node.js, of course

What benefits does Node.js have compared with other back-end technologies?

  • It uses an asynchronous non-blocking model that enables smooth multitasking.
  • It is easily scalable and very flexible and it also significantly enhances performance, particularly for applications that run real-time operations (chat, online gaming, video conferencing, etc.)
  • Front-end developers are usually already familiar with Javascript, hence the transition to back-end development through Node is almost entirely hassle-free.
  • It offers a clearer pathway to full-stack development. An application can be built entirely with a single programming language, using Javascript for the front-end and its extension, Node for the back-end.
  • Single-threading, even though limiting its capability to handle CPU-intensive applications, removes the issue of overheads. But with lightweight applications, it is not necessary to use multiple threads.
  • Well-known companies that develop the backend of their apps using Node.js include Microsoft, PayPal, Amazon, Netflix, Uber, and LinkedIn.

What is event-driven programming?

At this point, you are already moving towards the Node.js technical interview questions stage. Such questions are meant to probe the developer’s technical understanding of Node.js programming at the basic level, of course.

Get Node.js specialists salaries report
Ukrainian developers' salaries report

Because of the single threadedness of Javascript, the Node.js architecture is event-driven. It uses asynchronous callback functions to ensure concurrency. The event loop framework monitors events and once triggered, calls the Event Handler callback function. The EventEmitter module allows the application to maintain the event-driven programming model.

How does the event loop work?

The event loop is the framework that manages events, executing callback functions in the queue. It is responsible for its asynchronous and non-blocking I/O. Every program automatically creates a thread within which there is an event loop that schedules operations to be performed by the thread based on some preset conditions. Note that there is only one thread here; it’s the event loop that determines which callback functions to be executed by the thread at any given point in time.

Which libraries are most commonly used in Node.js?

There are several efficient libraries out there; only a few popular ones are covered here. Most libraries are hosted on the NPM website.

A list of the most popular Node.js frameworks
  • Express is a lightweight, minimalist, flexible, and perhaps the most popular Node.js library.
  • Nodemailer allows you to send emails from Node.js.
  • Gulp is a useful toolkit for automating your workflow.
  • Lodash is a modern JavaScript utility library delivering modularity, performance & extras.
  • Cheerio is renowned for its lean implementation of core jQuery

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

Package.json is essentially the manifest of a program. The file, found in the project root, includes all the various metadata associated with the project including applications, modules, libraries, packages, etc. Being the core of the project, the package.json file makes the program reproducible. The only two fields required of the package.json file are the name and the package deals.

Besides those, there are no requirements as to what the package.json file can contain as far as it’s in the JSON file format and is readable by other programs.

Mid-Level Node.js Interview Questions and Answers for Intermediate Coders

Node.js backend developer interview questions for 2 years experience and above usually test both theoretical and practical programming skills equally. On the one hand, you need to determine that the developer has the right Node.js coding foundation and experience through evaluation.

A guy is asking about difficult things

On the other hand, you also expect that the developer can handle the more technical aspects of the Node.js backend code together with other members of the development team efficiently. Therefore, prepare to ask them to explain the types of API functions (theoretical) as part of the Node.js programming interview questions, and also describe practical steps to debug an application.

What are the promises?

Promises represent objects with an indeterminate value of future successful execution or failure. It is like a ‘proxy for a value that will eventually become available.’ Promises help developers to deal with the asynchronous code model and avoid falling into callback hell. The state of a promise event can be pending, fulfilled, or rejected.

Describe the two main API functions in Node.js

  • Asynchronous, non-blocking: since Node.js depends on Javascript’s single thread to manage operations, performance becomes painfully slow. Instead, using this API function, one can execute multiple operations at once without having to wait for the server’s response at each stage.
  • Synchronous, blocking: a synchronous model queues threads and performs one operation only when the other is complete. This is good for a multi-thread framework but does not fit Node’s single threading
Check Node.js developers availability
resources availability ProCoders

What are the commonly used frameworks in Node.js today?

  • Express: Express is favored for its minimalist approach as well as its flexibility. Prominent Express features include basic routing, model-view-controller (MVC), middlewares, etc. and its focus is improving performance.
  • Koa: Koa is hailed as the next-generation framework and it’s developed by the team behind Express and the main difference between both is that the former lacks middleware. Also, Koa improves on Express by providing more customization options.
  • Hapi: this is a commercially-focused framework that is used by big websites such as PayPal and Disney. It is known for features like onPreHandler, code reusability, and stronger security
  • Nest: Nest is an enterprise-grade framework that is built for easy scalability. It has extensive library support and uses progressive Javascript
  • Adonis: yet another MVC framework, Adonis is loved by developers for its ease of use; it uses Laravel’s approach, after all. Its unique feature is that it has its own Command Line Interface (CLI)

How do you decide if Node.js is suitable for a particular application?

Node.js technical interview questions are aimed at revealing how the developer would handle practical issues.

A developers fixes bugs

The unique features of Node.js (single-threading, scalability, asynchronous non-blocking, etc.) make it suitable for developing:

  • Real-Time applications (live chat and instant messaging): an event-based and non-blocking model is the best fit for an application that has to handle several real-time servers, even though counterintuitively. Node.js, despite being single-threaded, is capable of handling multiple simultaneous requests via the event loop
  • Collaborative Tools: Trello, a globally renowned collaborative tool is built on Node.js. Collaborative tools require several updates at a time, and mostly in real-time
  • APIs are the most popular type of applications. API developers benefit from the lightweight nature of Node.js in building API apps quickly
  • Web streaming applications: the very nature of streaming matches the Node.js perfectly. Streaming involves sending several bits of data in small batches, rather than as a single package. That Netflix is based on Node.js is enough proof that you need

How do you avoid the callback hell?

First of all, a developer can deal with nested callbacks (which often lead to callback hell) by writing comments to explain complex lines of code. It not only helps the writer of the code to keep track of the series of callbacks, but it’s also so that someone else may be able to make sense of the code. One can also reduce code clutter by declaring functions beforehand, assigning names to functions for organization, using modules, using helpers from Async.js, etc.

To avoid the callback hell itself, one may split a complex series of nested callbacks into multiple, simple functions. Or simplify the complex nest by using promises.

How will you debug an application?

According to official documentation, using the –inspect switch, the Node.js program tries to find a debugging client. Once connected, you can use the Inspector client to start the debugging process. There are different open source Inspector clients that come in handy:

  • Node-inspect is a CLI debugger that uses the Inspector Protocol, is supported by the Node.js Foundation, and has a version bundled with Node.js by default though an update can be installed independently.
  • Chrome Dev Tools (55+) and Microsoft Edge: on a chromium-based browser (like Chrome, Edge, Opera, or Brave), you can run chrome://inspect or edge://inspect (for Edge only)
  • Visual Studio: the code editor is built-in with Node.js debugging support. The configurations are stored in the launch.json file in the .vscode folder. Launch ‘Node.js’ to begin setup.
  • JetBrains: JetBrains Webstorm uses the –inspect code to run Node.js debug configuration.
A meme about debugging

What is Crypto in Node.js?

Crypto is a module that provides the framework for encrypting data and handling encrypted data. Or more technically, the crypto module is a wrapper for OpenSSL cryptographic functions. It supports calculating hashes, authentication with HMAC, ciphers, and more!

What’s the difference between Node.js and Angular.js?

This is one of the most commonly asked Node.js technical interview questions. Node.js and Angular.js are commonly spoken of together that a non-developer could even mistake them for each other or think they perform the same functions. They are both open source technologies based on Javascript. But beyond that, what? As a beginner, one of the basics you’d be learning would be the differences between Node and Angular, outlined in the table below.

Node.jsAngular.js
It is a runtime environment based on Javascript. It is also cross-platform as it is written in the languages Javascript, C, and C++A web development framework that’s written entirely in Javascript
A server-side model. That is, it is useful for building the back-end of applicationsA client-side framework used to develop the front-end of applications
Installation is needed to use Node.jsAngular.js files need no installation; they are simply embedded in the codebase
It has different frameworks such as Express.js, Socket.io, Nest.js, Hapi.jsAngular.js is a framework itself

Advanced Node.js Interview Questions and Answers

These are more technical Node.js interview questions and answers for experienced developers. Of course, they are challenging questions.

That’s because, as a technical leader, you do not only seek to know if a developer has any knowledge of Node.js; you perhaps already assume they do. What you need from them here are answers to questions on how to handle the practicalities of coding with Node.js.

The Rock faced a challenge

For instance, ask to know how they can overcome practical challenges in Node.js such as single-threading and concurrency. Their knowledge should not be limited to only Node.js; they should understand how backend development works. That’s why you need to probe them with certain Node.js backend developer questions.

A Node.js programming expert should also have to look the part when attending to questions during the interview, whether it takes place physically or virtually. Their demeanor must be convincing and their approach to the questions should prove their expert status. When answering questions during the interview, make them feel free to draw upon illustrations, particularly from their past projects using Node.js to code.

What are some drawbacks of Node.js?

  • It has an unstable API due to frequent updates and a lack of backward compatibility. Developers need to continually change their code each time there is a new version of the API.
  • It is favored for its lightweight nature but that also means a suboptimal performance when development is CPU-heavy. The introduction of ‘worker threads’ in 2018 does not entirely solve this challenge either
  • Asynchronicity can be challenging as well leading to what is called a ‘callback hell’. This is “a situation where callbacks are nested within other callbacks several levels deep, potentially making it difficult to understand and maintain the code.” This creates performance issues for the application
Pennywise is suggesting Node.js
  • Javascript, the language upon which it is based lacks robust library support, compared to other programming languages. Developers resort to the common library for tasks such as Object-Relational Mapping (ORM), XML parsing, database operations, image processing, etc

You may use this as a trick question. When the candidate mentions a drawback, follow up with another question about how they would overcome that challenge. Keep them on their toes.

How does Node.js handle concurrency despite being single-threaded?

It can technically run parallel operations, that is, without having to switch back and forth between both. Indeed, it is single-threaded, but to handle multiple operations concurrently, it delegates I/O operations to the OS kernel, using the libuv library. After all, modern operating system kernels are usually multi-threaded. This makes Node.js run even faster than multi-threaded runtime systems, even with its single threading.

What are the streams?

Streams are like pipes that read data from a source and transmit the same to a destination sequentially. Streams are what enable Node.js to work with streaming data on apps such as Netflix. Typically, programs read files into memory non-sequentially, waiting until a file is read completely before processing it.

However, streams process files sequentially without relying on memory. Using the water pipe analogy, say you want to water your garden, the traditional model will involve waiting for all the pipe to pass through to the can completely before you start watering. However, with streams, while the pipe is still running, the watering takes place, meaning that there is no need for a can or storage.

A guy is calculating

The major benefit of using streams is efficiency: both in memory and time. For instance, where the size of a file that needs to be read into memory is bigger than the memory itself, the only option you have is to use streams to read the file in bits and save memory space. Streams are quite powerful when working with really large amounts of data.

Explain the types of streams available in Node.js

There are four types of streams, named after the actions they perform and explained as follows:
Readable streams allow you to read data from a file, for instance, fs.createWriteStream().
Writeable streams allow you to write data on a file, for instance, fs.createReadStream().
Duplex streams allow you to read as well as write data, for instance, net. Socket
Transform streams are a type of duplex streams where the output is transformed by the input and data can be transformed as it is written or read, for instance, zlib.createDeflate().

What is REPL in Node.js?

The REPL programming environment enables the interactive execution of commands. The four functions performed by REPL (from which it gets its acronym) are: Read, Evaluate, Print, and Loop. It is also referred to as ‘Node shell’. Basically, “The shell reads JavaScript code the user enters, evaluates the result of interpreting the line of code, prints the result to the user, and loops until the user signals to quit.”

What are some common REPL commands?

REPL CommandAction Description
<.help>Display help on all the commands
<tab Keys>Display the list of all commands.
<Up/Down Keys>See previous commands applied in REPL.
<.save filename>Save the current Node REPL session to a file.
<.load filename>Load the specified file in the current Node REPL session.
<ctrl + c>Terminate the current command.
<ctrl + c (twice)>Exit from the REPL.
<ctrl + d>Exit from the REPL.
<.break>Exit from multiline expression.
<.clear>Exit from multiline expression.

What is tracing?

The tracing module, enabled via the trace_events function, enables you to trace information generated by V8, userspace code, and Node.js core in a central system. This is done by first determining the pattern of node application and monitoring that data functionally and systemically. Tracing helps by giving performance insights that may be useful for identifying errors and dealing with memory problems.

What is libuv?

Libuv is a multi-platform support library originally written in C for Node.js. It uses asynchronous I/O. It was introduced in 2009 with Ryan Dahl (the creator of Node.js) claiming that ‘I/O needs to be done differently’. Now, libuv is used also by Luvit, Julia, Neovim, pyuv, etc. Libuv provides the framework for a developer to handle child processes, file and file system operations, worker threads, polling, streaming, signal handling, etc.

Ryan Dahl
Ryan Dahl

How does the Timers module work in Node.js?

The Timers module is used to schedule code execution. You don’t need the require() keyword to import timers since the Timer object is a global object. The timing utilities available are setTimeout, setImmediate, and setInterval. setImmediate is used to direct the immediate execution of a function once the current loop cycle ends. setTimeout is used to count down to the execution of a code at a given time. setInterval is used to schedule repeated execution of a particular function.

What are the middleware functions?

Middleware functions are used to modify the request objects (known as req) and the response objects (known as res). This is required to end the req-res cycle. The functions work by granting access to the req and the res. There is another parameter besides the req and the res, which is the next function. Calling the next() function ensures that the request does not hang and go to timeout.

Middleware mostly surfaces in the context of Express.js. Coding with Express.js should come with the assumption that middleware functions are activated immediately even if not immediately apparent. After all, even the Express official website says that “an Express application is essentially a series of middleware function calls.”

Let’s check which developer fits you!
Слой 0 3

What are global objects?

Global objects (or simply, globals) are objects that are available in all modules, hence the name. The following variables listed below are usually described as global objects but technically, they are not, since they still operate at the module level. Many confuse them for global objects because they are built into Node.js and are embedded in Javascript.
__dirname
__filename
exports
module
require()
Instead, it is better to refer to them as pseudo-globals.

The true globals are listed below:
global
process
console
setTimeout(), clearTimeout(), setInterval(), clearInterval() (these four are part of the Timers module)

What are Child processes? What’s the difference between spawn and fork?

Node.js is limited because it is single-threaded, yet it is still scalable because a developer can take advantage of multiple processes. This enables one to be able to handle much workload that a single thread and a single process wouldn’t have been able to handle. Developers can create and handle child processes in Node.js using the child process module. These processes interact with each other and that is how Node.js got its name: the cross-interaction of nodes.

Spawn() and fork() two of the four ways to create child processes. The other two are exec() and execFile(). Spawn is used to run system commands and once run, does not execute any further code within the process. In running a command that is within another command does fork come into play. Fork is a type of spawn that runs a fresh instance of the V8 engine and is used to establish communication between parent and child.

Conclusion

That is how to prepare for a Node.js backend developer interview. A Node.js coding interview is quite easy if you approach it the right way. At ProCoders, all our Node.js backend developers are capable of answering these questions and more to prove that they have the right expertise to handle projects for our clients. So far, we have racked up excellent reviews all the way.

Let’s schedule a call to discuss all your needs!

Write a Reply or Comment

Your email address will not be published. Required fields are marked *

Get Node.js specialists salaries report
Check Node.js developers availability
Please choose the experience level:
Let's check which developer fits you!
Which technologies do you use?

Our site uses cookies and other technologies to collect data to analyze our site’s traffic and to improve the quality of services. By using our site, you accept use of cookies, as well as the use of other tracking technologies. 
Learn more about our Privacy Policy.

Thank you!
We are already checking the information you just shared with us!