ReactJS Interviews - Strategies and What to Look For

React remains one of the single most used and loved app development libraries out there. React positions come with both benefits and drawbacks. Its popularity, driven by React’s simple declarative API, and highly flexible application deployments, makes the developer marketplace a highly competitive one when it comes to attracting high-quality ReactJS talent. However, if you’re looking to build reliable, robust, and attractive web apps using well-established and proven technologies — there are few libraries out there that can truly compete.

Hiring ReactJS developers to build premium-level apps is your best chance to stand out in a highly crowded marketplace. Doing so requires singling out high-quality developers from those that merely have a passing interest in the tools. This process begins with HR managers preparing to hire the best devs. Read the guide we’ve put together in our article: “A Comprehensive Guide to Hiring ReactJS Developer Teams”.

Qualities, experience, and the skills you bring out in developers during the interview process will help to highlight the perfect candidate during a ReactJS interview. Good interview techniques will illuminate hard-won knowledge and know-how among the right engineers. Outlined below are ReactJS interview questions and some example answers which will bring out the best of these developers. We’ve also included some of the qualities to look out for and answers to expect to help you recognize your company’s next leading dev star.

Going above and beyond this comprehensive guide, we can help you select the right company to handle ReactJS development for you. Tell us what you need. We can do the work for you and connect you with up to 5 companies within 72 hours.

Responsibilities of a ReactJS Developer

Before HR managers dive into asking who you want to hire, it’s worth looking carefully at what qualities your ideal front-end developer will have. Understanding the qualities you need will help guide your decision-making to land the precise candidate you’re looking for.

Write Clean and Maintainable Code

The first and foremost skill of any developer. Clean, clear, and easily understood code should be number one on the list of priorities.

This means code that is easy to read, well understood, and able to be modified by someone other than the developer who first wrote it. A developer who writes clean code saves time on scaling, maintenance, and debugging for weeks, months, and years to come.

Participate in Every Stage of the Development Lifecycle

While not necessarily an expert in every area, an experienced React developer should have some input at every stage of application development. Expressing an opinion in all phases, from initial planning to deployment and support, can prevent issues from arising later. ReactJS professionals with a great deal of experience in personal projects may even have practical knowledge and experience in every phase.

Asking about side projects during the interview can be a great way to find out what experience a developer has alongside their professional credentials.

Strong Problem Solving and Critical Thinking Skills

A major part of application development is practical problem-solving. This should extend outside of just working code into the code of underlying libraries and systems that support it. A developer with strong problem-solving skills can save hours and days throughout a single project without even realizing it.

Awareness of ReactJS Current Trends and Other Technologies

The software industry moves fast; it’s a practical requirement for developers to keep on top of what’s changing and what updates are happening within it.

This know-how shouldn’t necessarily be complete, by any means, but a general awareness of available tools and technologies is a valuable asset to have. An opinion on the advertised features and potential for such tools is even better still.

If you are preparing for an interview and need to brush up on recent trends in React.JS, we have you covered with our article on the future of ReactJS development.

Generalized Interview Questions and Techniques for ReactJS Developers

There’re three core parts that an HR manager should consider for their next interview:

Passion Projects

Starting off the developer’s interview with an easy question can be an ideal icebreaker. It helps calm inevitable pre-interview nerves and serves as a jumping-off point to frame questions about software development principles and practices.

“Do you have a passion project?” The answer a candidate gives to this question can help shape the rest of the interview, providing a reference point against which to evaluate technologies.

The Code Analysis Stage

Before a candidate has come into a ReactJS interview, the manager should have already looked at code available either as part of the application or available publicly in a Git repository or similar.

Existing code already in use is the best possible view you’ll get of how well a candidate will write code in the future. You can get into even greater detail by asking candidates to talk through features they have implemented or choices they’ve made when building web apps.

Description of Development Method of a React Web Application 

Describe how you would tackle the development of a React web application from requirements through to delivery. With this generalized starter prompt, you should begin to get a good feel for an applicant’s experience and expertise. It’s a valuable window into how they view the process of building a ReactJS app and the areas they pay more attention to than others.

Good answers that interviewers should look for should include a reasonably detailed explanation of requirement analysis, specification writing, planning, development, testing, and deployment. 

If you want a more detailed answer, it would be reasonable to dive further into this question, perhaps asking for a breakdown of how much time to allocate to each. You might also ask about common problems they’ve faced during development, such as changing requirements or a delivery date brought forward, and ask how this would affect things.

What to Look for in a ReactJS Developer

ReactJS is a highly popular technology amongst both professionals and enthusiasts. Like other highly popular technologies out there, that means it’s relatively easy to pick up and try out. Professional use, in skilled hands, takes much more time and effort.

The skills and experience of various ReactJS developers may be somewhat varied as a result. Even two highly qualified React developers are likely to have taken very different paths to get there. There’s a vital set of skills expected of any React developer at a professional level. Let’s go over them!

Hard Skills of a ReactJS Developer

• Expert knowledge of JavaScript in a production environment. Writing good JavaScript code is essential to understanding the underlying architecture.
• Expert knowledge of related components, tools, and frameworks. Developers with more than a passing experience with React will be familiar with tools such as React Router, Redux, or Material Kit React.
• Detailed understanding of React’s concepts and structure. Understanding the Virtual DOM, JSX, component lifecycle, as well as the latest updates about React are essential to get up and running as a ReactJS developer.
• Strong background in ES6, HTML/CSS. These are essential components in front-end development.
• Experience in unit testing, Git, and Continuous Integration(CI)/Continuous Delivery(CD) tools. Each has an essential role to play in developing modern apps.
• Experience with REST API/GraphQL. Something you’d expect of ReactJS devs for integrating with third-party platforms.

Soft Skills of a ReactJS Developer

• Strong communication skills and an open-minded approach to working with others. One of the most overlooked abilities of skilled software developers is the ability to communicate ideas well and accept the opinion of others.
• Desire to learn. The software industry moves fast, and its tools are consistently improving. Good developers should always be looking to improve their skill sets and increase their value and abilities.
• Transforming requirements and goals into technical specs and code. An ability that pays dividends in being able to work on applications from the initial stages through to completion.

Skills Questions for ReactJS Developers

Implement Linear Search in JavaScript

Used in a ReactJS interview, this question tests both knowledge of data structures and algorithms and demonstrates some basic knowledge of JavaScript too.

function linearSearch(array, key){

let results = []

for(let i = 0; i < array.length; i++){

if(array[i] === key){

results.push(i)

}

}

if(!results){

return -1//empty array

}

return results

}

}

Describe how you’d build a single-page application with multiple sections using ReactJS

Another short and simple test that demonstrates an understanding of the technologies you’re interested in. If the candidate has access to a computer, you may ask them to implement the page instead. Doing this as a pair programming exercise can be a great (if stressful) way to see how candidates work under pressure.

Describe some steps you might take to improve the performance of a web page. Most candidates should have some ideas to bring to the table to improve loading times. Some of these might include:

• Using adaptive images
• Compressing content
• Cache improvements
• Combining images into CSS sprites
• Enabling HTTP Keep-alive response headers
• Minify Javascript and CSS

Candidate Technical Interviews for ReactJS Engineers

Technical interviews, in software development, are notorious both inside and outside the industry for including gotcha questions and irrelevant exercises. Conducting a good ReactJS interview should mean avoiding both of these.

Employing the tactics used in the early 2000s gives a bad impression of your business, makes your environment look like one where candidates won’t want to work even if they do get an offer, and teaches you very little about strong candidates. You can find out a great deal about the right candidate with nothing more than just discussing the concepts and ideas that a react developer should know.

The best dev candidates, the ones that will fit in well and create the most productive employees, can articulate their opinions on technical topics and draw from experience to inform their answers. The perfect ReactJS role candidate will be able to take on board the opinions of others and move the discussion forward accordingly. Alongside interview questions, in-depth programming exercises are another excellent way to allow a candidate to demonstrate their skills and experience.

When it comes to the ReactJS interview, honest discussion with candidates is worth ten times that of a formalized quiz or interrogation. The questions below should simply help to inform that discussion, acting as a jumping-off point to go into each applicant’s personal experiences with the tools and technologies. Doing things this way, you’ll find out far more about both soft and hard skills—figure out where they might fit in well and maybe even learn a thing or two about ReactJS development in the process.

We can also help you with selecting the right company, tell us what you need. We can do the work for you and connect you with up to 5 companies within 72h that match your need.

ReactJS Interview Questions to Ask All Candidates

What is React.JS?

This question is a fit for entry-level or internships in ReactJS roles. A candidate should answer this question with the following:

“React is a JavaScript library for building user interfaces. It's used at Facebook and Instagram, and was created by Jordan Walke, one of the engineers who built Instagram. React targets UI components as the basic unit of code reuse, and it makes it easy to create reusable UI components. It's also very fast and flexible.”

Great candidates will also go over describing the benefits of using React over other libraries like Angular or Ember:

“The main benefit of using React is that it's relatively easy to learn and use compared to other libraries (Angular). This makes it ideal for new developers who are just getting started with frontend development, or even experienced developers who want something that doesn't require as much time learning how to set up an application structure or learning how each component works together within an application (Ember).”

How is React different from other JavaScript Frameworks?

A candidate’s own experience with other JavaScript frameworks will inform their answer to this question. The core of an answer should include React’s focus on the creation of components and the agnostic relationship it has to an app’s underlying architecture. The listed advantages might talk about the additional flexibility React provides developers.

A good follow-up question for your ReactJS candidate would be to ask when they might choose React over one of the other technologies they’ve used in the past and why.

Describe the lifecycle of a React Component.

The component lifecycle is the key part of React. Broadly, components have lifecycle events in three main stages:

• Initialization
• State updates
• Destruction
• What is JSX?

When React was first launched, it simultaneously launched with JSX—a syntax extension to JavaScript created by Facebook.

Developers do not have to use JSX to write React applications, but it has become a de facto standard within React.JS. A candidate with sufficient experience should be able to talk about the pros and cons well.

What are Stateless Components?

State is a critical component of React so stateless components can seem somewhat strange.

Stateless components are simply pure functions that render DOM based on only the properties passed to them.

What is the StrictMode Component, and why would you use it?

StrictMode is included with React to highlight any potential issues within components. Potential issues are logged to the console in development mode to alert the developer of any issues. In production mode, these warnings are not shown at all.

Developers use StrictMode to stick closely to best practices and maintain high-quality code through the development phase.

What do you know about the Flux pattern?

Using Flux, the data store is a central authority for all data. Data changes must occur within the store from which they are broadcast to view via events.

Actions may be fired, controlled by a central dispatcher, to request changes in-store data. The advantage that this model has is that data stability is ensured and runtime errors are minimized.

List some common approaches to Styling a ReactJS Application.

Common approaches a developer will mention during a ReactJS recruitment process include:

• CSS Classes
• Inline CSS
• Pre-processors (Sass, Stylus, less)
• Css-in-JS modules such as Emotion, Styled-jsx, and styled components
• Explain the standard JavaScript toolchain

To unfamiliar developers, the JavaScript toolchain can seem overly complex. It’s important to have a good mental picture of how these pieces fit together.

A good answer should include:

• Dependency Management
• Linting
• Style-checking
• Transpilation
• Compilation
• Minification
• Source-Mapping
• What tools might you use to improve the accessibility of a React application?

Great ReactJS interview candidates will present the difference between static analysis tools and browser ones:

Static analysis tools:

Linting tools can be used to analyze React projects at the component level. These are low-cost, easy to use, and run very quickly early in the development phase. These should typically be the first line of defense against accessibility issues appearing.

Browser tools:

At an application level, browser accessibility tools such as Google Lighthouse can analyze accessibility to discover real-world issues. Ideally, these developer tools would be run in a CI/CD environment to pick up issues after the app has been deployed to test.

FAQs:

We’ve got a couple of extra facts we need to clarify before you’re ready for your next interview: 

Q1. How do you prepare for a React developer interview?

The interviewing process can be intimidating, but it doesn't have to be! The first thing you need to know is that there are many different kinds of interviews. This means that one company might ask very different questions than another company would ask. Therefore, it's best to practice answering questions as much as possible so that you're ready for anything!

When preparing for an interview, it's important to remember that the interviewer wants to see how well you know your stuff! They want someone who has experience working with React and knows how it works (and why). The interviewer will want to see if you can explain these things clearly and concisely — so don't worry about memorizing every little detail about React (yet).

Q2. What is JSX in React?

JSX is a JavaScript syntax extension that is used to describe the UI of a React component. It's a declarative language that allows you to write user interfaces in XML. It's not mandatory, but it's recommended for larger projects.

You can use React without JSX, but it will be more verbose and less readable than using JSX. JSX allows you to write React components in a way that resembles HTML markup, but with the flexibility of JavaScript. This makes it easier for programmers to reason about their UI and frees them from having to use separate tools for development, testing, and building production code.

Q3. What are some basic-level ReactJS interview questions?

Some basic level ReactJS interview questions that you can use in your next interview.

• What is React?
• Can you explain what JSX is?
• What are the different types of components in React?
• How to create a component using JSX?
• How to create a stateful component in React?
• What are the three lifecycle methods of a component in React?
• How to pass props to child components in React?
• What is the difference between state and props?
• What are some of the benefits of ReactJS?