React.js is one of the most popular JavaScript frameworks in the world. It allows developers to build large-scale web applications which are fast and easy to develop.

Developers are working with React.js to create some of the most cutting-edge applications we see today, and they're using it to build some of the largest and most successful websites on the internet.

When you hire a React.js developer for your business, you want someone who can help you create a product that will meet your business needs and be easy for users to utilize. You also want someone with experience with the framework, so they can guide you on how best to implement it for your specific needs.

The most important technical skills of a React.js developer

According to skilled React.js engineer and technical interviewer Terri Prifti, these are the three most important technical skills a React.js developer should have:

"A React.js developer should be able to write HTML + CSS and be aware of responsive web principles. They should also be familiar with JSX syntax and understand the fundamentals of JavaScript language (for example, data types, DOM manipulation, 'this' keyword, callback functions)."

Terri Prifti

He adds that a great React.js developer should be familiar with the following:

• Higher-order components (HOCs);
• Shallow rendering components;
• Being able to avoid prop drilling;
• Writing tests.

For Aldin Mahmutbegovic, a Senior Fullstack Developer skilled in React.js, he suggests that the candidate has great knowledge of JavaScript.

"I think the crucial thing is understanding JavaScript to be an excellent React.js developer. In my experience of working on solo engagements and with smaller and larger teams, I've noticed that some intern or junior developers dive directly into React without taking enough time to learn JavaScript in depth, beyond just the basics/fundamentals."

Aldin Mahmutbegovic

Aldin adds that as a result, when they get stuck with problems that demand debugging or changing a library's behavior, they often need help understanding the logic/functionality/code of the specific library/plugin. This shows us the importance of JavaScript skills before diving deeply into React to build a solid foundation for effective development and problem-solving.

He also suggests that a successful React developer must have excellent analytical skills.

"More often than not, developers are not working on projects created from scratch. Rather they are onboarded on existing tasks that might have a big code structure and complex architecture. A developer must have the necessary skills to analyze and understand the logic behind those applications."

Knowledge of code debugging is crucial to understanding existing code snippets' functionalities. More React-specific skills would mean understanding the concepts of state handling and routing in the React apps and keeping up to date with the frequent changes in React.js.

Hiring a React.js developer

The demand for React.js developers has increased tremendously in the last few years, showing no signs of slowing down. As a technology deeply rooted in the future of web development, many job opportunities exist for those who can become proficient with it.

On the flip side, the hiring process can be complex. With so many other companies needing React.js developers, finding someone experienced in the technology and dedicated enough to work for your company specifically can be challenging.

Hiring a skilled React.js developer can also significantly benefit businesses leveraging AI technologies. The developer's expertise in React.js ensures that businesses can create intuitive and responsive frontend interfaces, crucial for delivering AI-powered functionalities to end-users. Whether it's a recommendation system, natural language processing tool, or predictive analytics dashboard, a proficient React.js developer can seamlessly integrate these AI features into user-friendly web applications.

The key to hiring someone who will develop your engagement effectively is to ensure they are familiar with what you need to be done. Make sure they have experience working on tasks that have similar requirements and design goals as your task – that way you ensure they will work quickly and efficiently while still meeting your standards.

What makes the best React developer stand out from the other applicants?

A React.js developer is a special breed of engineer. They're the ones who can envision how to bring your product to life. As a hiring manager, it's your job to find out if a candidate is one of those top-tier engineers – and while you can't guarantee they'll be excellent at their job, there are certain things you can look for to help predict the probability.

Can they think on their feet and talk about React?

Do they know what makes React great or what it's missing?

Do they have experience working with it or just know how to use its documentation?

One thing that is only sometimes obvious is that there needs to be a definitive way to tell who will be a great hire and who won't. Everyone's approach is different, but some strategies can help:

• Assess their ability to think critically and creatively
• Assess their past work experience
• Test or interview them on their skills (we have a few interview questions prepared further down this guide)
• Make sure they are enthusiastic about working with you

Apart from these, Aldin suggests that a great React.js developer will know about state management since, nowadays, almost all the React app handles some kind of data (big and small), so that skill is crucial for being an excellent React developer.

"In addition, I would say that a great React.js developer must have the skills to write reusable and modular components since that is the key to building an optimized and scalable application."

Aldin Mahmutbegovic

How to assess a React.js developer quickly and efficiently

One of the most significant advantages of React is that you don't need a lot of prior experience with it to be able to create functional components – you can learn it as you go along, which is very helpful if you're looking for a junior developer who will be able to fill in the gaps as needed. With that said, there are some things you can look for in a candidate's portfolio that will help you separate the good developers from the great ones.

Aldin lists a practical approach to assessing the candidate:

• The best approach to assess React developers (and software all developers in general) is to check their background and the experience that they gained during their careers.

• After the initial check, a technical person who understands React in-depth should briefly interview the candidate to get to know them and assess their role in their listed tasks.

• As a last step, I would provide a “real-life" scenario/task to the candidate to investigate issues with a code/component to get their feedback about possible optimizations/fixes to the code.

A good React developer is always open to learning new things and strives to understand new frameworks or techniques, so looking at their blog or seeing what conferences they've attended could also help you make an informed decision.

Interview questions to ask

The best React developers are the ones who understand its benefits and can help you decide whether it's the right tool for your team and business.

During the interview, ask about their experience with React.js and how they would approach a specific task. This will give you a better idea of how well they know the framework and allow them to show off their abilities naturally. If they have past engagements using it, ask for examples of what they've built with it, or if that's not available, look for other tasks using similar frameworks. Here are some examples of technical questions you can ask during the interview and the example answers you should, ideally, receive:

1. What are the features of React?

Example answer:

The essential features of React.js are:

• JSX
• Components
• One-way Data Binding
• Virtual DOM
• Simplicity
• Performance

2. Why use React instead of other frameworks, such as Angular?

Expected answer: React outperforms Angular due to its virtual DOM implementation *and rendering optimizations. Switching between React versions is also simple since, unlike Angular, you don't need to install updates one at a time. Finally, various ready-made solutions are available to developers using React.

3. What is an event in React?

Expected answer: An event is a potential action that a user or system-generated event might bring. Events include mouse clicks, web page loads, key presses, window resizing, and other interactions.

4. What are synthetic events in React?

Expected answer: A cross-browser wrapper for the native event of the browser is a synthetic event. It has the same interface as the native browser events, such as preventDefault() and stopPropagation(). However, the events are universally functional across all browsers.

5. What is the difference between Hooks and Redux?

Expected answer: React Hooks features handle the local component state while Redux manages the global state and actions that can be dispatched.

6. How do you manage folder structure?

Expected answer: React doesn’t have a rule on how you put files into folders, but some more common approaches are grouping by features or routes or grouping by file types.

7. What is the React component lifecycle?

Expected answer: In React, each component has a lifecycle you can track and control throughout its three primary phases. Mounting, updating, and unmounting are the three steps.

8. How can you avoid component re-rendering?

Expected answer: To avoid re-rendering per component, use the shouldComponentUpdate() lifecycle.

9. Give me three advantages of using hooks in React.

Expected answer: React Hooks provides three benefits: reusability, readability, and testability.

10. How often does React useState update, and why?

Expected answer: React delays updating updates because developers utilize useState to improve speed by building queues. Candidates should know that useState updates happen asynchronously rather than immediately implementing changes to the state object.

11. What is the most significant benefit of using Flux?

Expected answer: You can control how data flows through your program by utilizing Flux. You may more effectively analyze data changes and troubleshoot issues by adopting a unidirectional data flow with predefined responsibilities for each component (action, store, and view).

12. How do you create refs?

Expected answer: React is used to build Refs. Using the ref attribute to attach to React elements after calling createRef(). When a component is created, refs are frequently set to an instance property to be used as references throughout the component.

13. How would you optimize performance in a React app?

Expected answer:

• By keeping the component state local, when necessary
• By remembering React components should avoid needless re-renders
• By code-splitting with dynamic import
• Through React's windowing or list virtualization
• With React's lazy image loading

14. What would you avoid binding in React?

Expected answer: I can use arrow functions in class properties to avoid binding in React. Class properties are a new feature; I must enable transform-class-properties to use them.

15. Tell us about previous engagements you’ve worked on that were built on top of React.

Example answer: I have worked on a messaging app/real-time chat app/personal blog/e-commerce mobile application.

Essential tools a React.js developer must be familiar with

For Aldin, he remains steadfast in his opinion that JavaScript is the key to understanding and working with React. In addition, knowledge of state management and, of course, HTML/CSS is imperative, he says.

"During my career as a developer, I worked with people who had excellent knowledge of React but lacked in-depth knowledge of HTML/CSS, which in my opinion is unacceptable regarding frontend development. One can’t call themselves a frontend developer without the knowledge of HTML/CSS and responsive design."

The tools needed to be a successful React.js developer heavily depend on the product they will work on. But some of the general tools that are a “must have" are:

• npm or(and) yarn
• web pack
• React Router
• some of the CSS preprocessors tools.

What makes React.js so popular today, and why do developers prefer it?

React.js has become immensely popular among developers due to its exceptional features and numerous advantages. One of the key factors driving its popularity is the efficient and flexible component-based architecture, which enables developers to build reusable UI elements, leading to faster and more maintainable development processes.

Aldin shared why he enjoys working with React.

"From my experience, some of the key benefits of using React.js are the reusability of the code, optimized rendering, and faster apps, and the plugins/libraries that the React ecosystem provides us."”

Here are more reasons Aldin thinks React.js benefits developers and companies alike:

• It boosts productivity.
• It brings the maintenance of the engagement/code to a new level.
• New developers who join the engagement find it relatively easy to onboard and understand the code/functionality of the engagement itself.
• From the company's perspective, using React makes it easy to scale the team if the architecture/code of the engagement is set up correctly.

Specific applications and industries that use React.js

React.js finds its best and most particular applications across various industries and domains. Its unmatched performance and flexibility make it ideal for building interactive and dynamic user interfaces, rendering it indispensable in web development.

Aldin believes using React to build the frontend of the apps is an industry standard.

"Since React.јs is a powerful and versatile library, it is suitable for various industries, including eCommerce, Healthcare, FinTech, social media, and all sorts of web applications, so there are no limitations to using it (React) in any industry. For example, its fast rendering and performance optimization provide an excellent solution for products that handle big data loads. Another example is that the modular and scalable nature of React.js is perfect for enterprise applications."

Aldin Mahmutbegovic