Expert Node.JS Interview Questions

Recruiting Node.js developers is an increasingly popular request from companies of various profiles. A 2020 StackOverflow survey provides that over 50% of programmers prefer to work with Node.js. This platform is used primarily for JavaScript backend development. According to experts, it is distinguished by a high development speed and a low entry threshold.

Hiring an expert node js developer can be a daunting task. There has been a lot of controversy about how to conduct interviews with software developers. Forget forever about questions like “Where do you see yourself in five years?” and “What attracted you to our company?” – they annoy candidates and hardly provide any insight into the candidate's relevance to the position. From the client's side, it’s important to evaluate a candidate's skills and their working experience with the platform. There is a basic set of knowledge and skills that can be used as a guide when interviewing candidates.

In this article, we’ve collected common questions that can be useful during a Node.js developer interview and will help you hire a team of experts.

What To Ask A Node.Js Developer?

The professionalism of a Node.js developer, be it a company or a freelancer, depends on a combination of hard skills (professional qualities) + soft skills (personal qualities).

Hard skills include everything that is directly related to the development process. This includes all the nuances of creating server applications and tools used. The technical knowledge test is the most important part of any job interview. Based on the test results, it’s possible to determine the developer's level. Here is a list of questions you can ask a candidate to assess their hard skills.

What is Node.js and where is this technology used?

Node.js is an open-source, cross-platform JavaScript runtime that runs on servers. The Node.js platform is built on Google's V8 JavaScript engine, which is used in the Google Chrome browser. This platform is mainly used to create web servers, but its scope is not limited to this. Node.js is suitable for a very wide class of backends, from online stores to educational services.

Node.js is an unusual technology. The modern JavaScript ecosystem was created by non-programmers, which is why it has a lot of fresh and unusual ideas. It's easier to get started writing applications in Node.js than in Java, Ruby, or PHP. Plus, this is a fairly mature platform, many problems have already been solved, and the best approaches are known and described.

Why choose Node.js?

The pros of Node js can be listed for a long time, but the most significant is the non-blocking I/O model. This system is event-driven and works asynchronously, building a priority queue. When thousands of people are connected to the server at the same time, it’s easier for it to cope with the load, since there is no need to create a separate thread for each connection. Appropriate resource allocation helps to handle more connections.

Moreover, this technology is improving rapidly. Thousands of programmers around the world are working on its development. It is difficult to underestimate the role of the community – it helps with difficulties, a lot of training materials, quickly found errors in the functioning of the system, the opportunity to discuss ideas or find a team. With a living community, technology is developing much faster, and all thanks to open source. The popularity and advantages of Node js didn’t go unnoticed, it has already been chosen by such companies as Google, PayPal, Netflix, Microsoft, Uber, Linkedin, Yahoo, Walmart, and others.

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

One of the most important advantages of the platform is asynchrony combined with an event-driven approach. Unlike streaming, event-driven programming is based on some kind of external action. The flow of the program depends on the user actions or the network packet received by the program. This solution simplifies the programming of interactive applications, i.e. based on work using I/O.

In addition, the advantages of the platform include:

  • Speed. Building a workload-capable prototype doesn't take a lot of time. The first stage, when the programmer forms the backbone of the future product, goes very quickly. If the architecture is well thought out, then in the future there will be no difficulties in extending the site to Node JS either.

  • Large and lively community. Because it is open-source, web developers can write and share different modules and packages. Modules often combine well.

  • JavaScript syntax. This provides relative simplicity and affordability.

  • Built-in library. It expands with each update, but even in the first version, there were quite ample opportunities.

  • Continuous development of the ecosystem. The number of ready-made modules and external libraries is constantly growing, which is facilitated by the use of npm.

  • V8 engine. It uses memory sparingly, is well optimized, and provides functionality for profiling the processor and memory.

What can one write in Node.js?

Using Node.js, a developer can create both a program for the web and for Linux, OS, and Windows. Using libraries, APIs can also be generated. Ways of synchronization of the mobile with the computer are added – when writing a text on the phone, it will be visible on the web and the PC / laptop. Unlike regular browser JavaScript, Node knows how to interact with global objects, including documents and windows, when building Windows applications. This opens the way to the user's hard drive and file system.

How to implement async programming in Node.js?

  • First class functions. We approach functions like data, scattering them around and executing them as needed.

  • Functional compositions. Also known as anonymous functions or closures, they are executed after something happens in the I/O.

  • Callback counters. By hanging callback functions on specific events, you cannot guarantee the order in which they will be executed. So, if you need to wait for the execution of several requests, then the easiest way to solve this problem is to count each completed operation, and thus check if all the necessary operations have been completed. This is useful if you absolutely need to wait for the results. For example, by counting the number of executed database queries in a callback, we can determine when all our queries will be executed, and only then go further. Database queries will run in parallel because the I/O library supports this (for example, thanks to a connection pool).

  • Event loops. You can wrap blocking code in an event abstraction by running it in a child process, and fetching data from that process when it finishes running.

Getting More Specific: Further Questions And Details

In some cases, it is necessary to check not only general knowledge but also a deep understanding of the Node.js development features. Here are some additional questions about Node.js you can ask a candidate to test their skills and expertise.

  • How does Node.js work with threads?

  • For which cases is the Node.js server good, and for which is it bad?

  • What is an event loop? How does the event loop work? What phases does each iteration consist of? What happens in each phase?

  • What are tasks and microtasks?

  • How to work with Node.js with large amounts of data? What are the types of streams? What is the difference between Duplex, Transform, and PassThrough streams?

  • How does the modular system work in Node.js?

  • What types of modules do you know?

  • What can you tell us about module caching?

  • What is process.nextTick()?

  • What is the child_process module used for?

  • What are the ways to scale a Node.js server?

  • How does memory work in V8? How does the Garbage Collector work? How to deal with memory leaks?

  • What are the pros and cons of microservices and monoliths? What are queues in Node.JS?

  • What can affect the security of Node.JS applications?

Hire An Expert Node.JS Developer

Node.JS is truly one of the most useful web development tools out there today. If you’re looking for expert developers, get in touch with Yojji team.

We’ve been creating products using the Node.js platform for many years. With the help of Node.js frameworks, our experts can significantly reduce the time it takes to develop an application without changing its logic. We often recommend our customers to use Node.js technology if the future project is an interactive service, with many user options, and a highly loaded system, i.e. involves a large amount of traffic and a lot of operations on the service. Yojji specialists will write functional code, create a user-friendly interface, develop a unique design specifically for your product.

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