React.js Interview Questions – How To Make Sure the Candidate Fits Your Project

What Questions to Ask During a React Interview?

There are three categories of React.js technical interview questions. They cover the technical expertise of the developer, their previous experience, and expectations towards the future project, along with personal traits to make sure the candidate fits you from all the points of view. 

Let’s consider React.js coding interview questions you are welcome to ask your potential tech team members. 

React.js interview questions to evaluate technical expertise

"What should I study for a React interview"you may ask? You, as a business owner, are better to study some basic concepts of React.js to be on the same page with the developers you are interviewing so that you can ask proper interview questions on reactjs. From the technical perspective, React.js is tough but from the practical and business standpoint, the technology and its benefits are understandable enough.

So, let’s start with the simple React js interview questions. 

• What is React.js? 

This is a tricky question since some resources consider React.js to be a library, while others can call it a framework. According to our technical experience, React. js fits the concept of a Javascript library for building user interfaces, and thus shouldn’t be called a framework.

• What is virtual DOM?

A virtual DOM, or reconciliation, is a concept that allows a virtual prototype of the UI to be kept in memory and synced with a real one using a library. 

• What are the business benefits of virtual DOM? 

This is one more tricky question, the answer to which will show the understanding of React.js not only from a technical but from a business standpoint since virtual DOM allows for creating more performant apps. 

so, these are the very basic reactjs interview questions and answers. And here are the React.js interview questions for experienced programmers. 

• What are the components in React?

React components are the app’s parts, to put it simply. Technically, they are pieces of JSX code. 

• Does React.js support server side rendering or client-side rendering?

React.js supports client-side rendering. 

• What is a callback function in React.js?

A callback function is a tool to change the child component and prevent data loops.

• What is the biggest technical challenge with React.js?

Some developers consider JSX a challenge. JSX, in turn, is an extension syntax on the verge of JavaScript and HTML, but not all the React.js components should be written in JSX  - sometimes JavaScript will be required. 

Another challenge is that in some cases, React.js documentation is difficult to go through either.

React.js experience interview questions to make sure the candidate fits your project

This is another important category of React.js advanced interview questions and answers since they allow you to make sure that the candidate fits your project from a business perspective. Here is what you can ask:

• What is React.js good for?

React. js is good for Single Page apps, Dynamic content apps, eCommerce websites, and projects with complex architecture striving for high performance. 

• What made your previous team choose React.js for the project you have worked on? 

Answering this question, the candidate is likely to highlight the main specific feature of the previous project, so be attentive  -  there is a chance the insight they share can fit your project as well. 

After you are done with some general questions, get back to the candidate's portfolio and CV, make sure they have worked on the projects in your niche and then, ask more detailed questions about the candidate’s previous experience. 

For example:

• Considering your portfolio, what was the most challenging project you have worked on?
• What made this project challenging?
• How did you handle the tasks you have faced? 

Asking these questions, be attentive to the answers, as the developer may point out to both technical complications and pitfalls, as well as to the communication, culture, management, and environment in the team they have worked in. Their answers will give you a hint at what the candidate considers to be acceptable/unacceptable at the future workplace.

Basic React.js interview questions to verify soft skills and personal traits

After there is no doubt that the candidate has enough technical expertise, a deep understanding of the ways React.js benefits software development from a business standpoint, and a good level of experience, proceed with asking questions aimed at evaluating the soft skills and discovering the programmer's personal traits. Below are some ideas:

• Are you a team or individual player? What made you choose such an approach?
• What makes an environment in a team healthy?
• Suggest a strategy to manage a disagreement in a team. Suggest a strategy to manage a disagreement in a team under the pressure of a deadline.
• How can you evaluate your communication skills?
• What values should a software project pursue to make you sincerely committed to it?
• Do you prefer to work at home/in an office/other option?
• What are you learning/reading now? 

This list of react interview questions can be continued. You are free to ask the ones you consider important for your project but don’t go too personal.

Advanced ReactJS Interview Questions

If you need a specialist to work on a complex project and to know all the nuances of ReactJS, it is not enough just to ask basic ReactJS questions, you need to make sure that the candidate fits perfectly into your project and has the required knowledge and experience. In this case, asking advanced ReactJS questions will be very helpful. Let’s now look at the most common reactjs advanced interview questions for determining the level of React.js developers and their skillset.  

Popular advanced ReactJS interview questions

Here is the list of the most popular react js interview questions and answers.

• What is the significance of “keys” in React?

“Keys” in React, first of all, are important in terms of identifying distinctive VDOM Elements with their corresponding data that drive the UI. They are also helpful in identifying the items that changed, are added or removed.

• What are some key features of the ReactJS?

The key features of the ReactJS are as follows: ReactJS uses Virtual DOM instead of RealDOM, ReactJS employs unidirectional data flow, React mostly uses Server-side rendering, and ReactJS allows for Data Binding.

• What are the most frequent approaches for styling a React application?

The most common approaches are: CSS classes, Inline CSS, CSS-in-JS Modules (Styled Components, Styled-jsx, and Emotion) and, Pre-processors.

• What are synthetic events in React?

Such events incorporate the response of various browsers’ native events into one API and ensure that the events are in accordance with various browsers.

• What are portals in React?

Portal is the way of rendering children into a DOM node that exists outside the DOM hierarchy of the parent component. It’s a recommended way for such type of rendering.

• What is the use of an arrow function in React?

An arrow function is used for writing an expression in React. It makes it possible for users to manually bind components. When you are working with higher-order functions, the functionality of arrow functions can become handy.

• What is Redux used for?

Redux is used for storing the state of the application in a single entity. This simple entity is usually a JavaScript object

• Can you explain, what are Higher-Order Components (HOC) in React?

A higher-order component (HOC) is a function that takes one component and brings back a new component. Essentially, it’s a pattern that is derived from the compositional nature of React.

• When is HOC mostly used?

HOC can be used for many use cases. For example, it can be used in the following situations: state abstraction and manipulation, rendering Hijacking, props manipulation, logic, bootstrap abstraction, and code reuse.

• Can you use AJAX with React?

Yes, you can. Any AJAX library can be used with React. It is just important to maintain the states of the components. And the props should be passed from the parents to the child components.

• What are synthetic events in React?

Synthetic events in React are objects that act as cross-browser wrappers and make it possible to use the native events. This is done to guarantee that different browsers can run the API and that the event contains all the properties.

• What's the main difference between a Controlled component and an Uncontrolled one in React?

A Controlled component takes its current value via props and notifies changes through callbacks such as onChange.  And an Uncontrolled component is the one that stores its own state internally, and it is a bit more like traditional HTML.

• Can you name some of the performance optimization strategies for React?

The most common performance optimization strategies for React  are: utilizing useMemo  (a React hook that is used for caching CPU-Expensive functions) and  Lazy Loading, which is a technique used to reduce the load time of a React app

• What is the disadvantage of prop drilling?

The disadvantage of using prop drilling is that the components that must not be aware of the data, do have access to the data. Besides, the code becomes more difficult to maintain. One can avoid prop drilling  by utilizing the Context API or some form of State Management library.

These are the main react js advanced interview questions. If the interviewee answers all of them properly and ideally, with the examples, you can be sure that such a developer has extensive knowledge and can work on complex projects. Yet, at times, it might be worth asking some additional react advanced interview questions to double check if the candidate knows all the details or, perhaps, give a candidate additional chance if you consider their answers not precise enough.

Additional advanced ReactJS interview questions

Here’s a compiled list of additional advanced react interview questions.

• What is StrictMode in React?

StrictMode in React is a type of a helper component that will assist with writing better react components. It will also help prevent some side effects by identifying potential risks as well as verify that the components inside act in accordance with some of the recommended practices and warn you if not in the console.

• What are portals in React?

Portal is a suggested way for rendering children into a DOM node, which exists outside the DOM hierarchy of the parent component.

• How to re-render a React component?

React automatically Re-renders the components every time any of its props or state is updated. Class components supply you with a built-in method to trigger a Re-render. In order to force React to Re-render the component, you can just use the forceUpdate method.

• Why is it not advised to update state directly?

It’s not a good idea to update state directly since then it won’t re-render the component. Instead, you can use the setState() method. It easily programs an update to a component’s state object. And when the state changes, the component answers by re-rendering.

• Why is a router required in React?

A router is required in React since it is used to manage multiple routes every time a user types in a URL. When the route is present in the router for that corresponding URL, then the user is easily transferred to the particular route.

• Can you name the predefined prop types present in React?

These are the main predefined prop types in React: PropTypes.bool, PropTypes.func, PropTypes.node, PropTypes.number, PropTypes.string.

• What are Webpack and Browserify? Are they different?

Both Webpack and Browserify, render the code for use in a specific place. But they aren’t entirely the same. For example, Webpack comes up with many tools by default, and, in contrast, Browserify can only do this after downloading the add-ons. Webpack is a popular module packaging system built on Node.js.

The Most Effective Way to Hire React.js Developers 

Hiring React.js developers seems to be the most intuitive option, still, this strategy isn’t always the most cost-effective and easy to implement. On the contrary, this is the most expensive approach to hiring tech talents, plus it obliges you with additional spendings and requirements you should be compliant with as an employer. 

As a smarter option, you can consider outsourcing your software development. In its classical approach, outsourcing means hiring a remote team that can be either already gathered and ready to start, or gathered from scratch by the development vendor according to your project requirements. Both of the options can promise significant time and money savings, plus the opportunity to get started with the development process almost instantly, having no obligations except for those specified in the outsourcing contract. 

Choose between team staffing and team extension

Software development outsourcing is pretty flexible, so, depending on your project specifics, requirements, and the talents you may probably already have, you can also consider such opportunities as team staffing and team extension. Both options are aimed at cutting costs and speeding up the start of the development process.

Team staffing means gathering a team of React.js developers from scratch, according to your project requirements, while team extension or scaling means strengthening the team you already have in-house with remote specialists. The latter tactic is perfect when you have to develop your solution at a rapid pace but face a  shortage of hands. 

Partner with a reliable React.js development vendor

If outsourcing your software development and hiring a React.js developers team remotely suits your project, the next step is to partner with a reliable development vendor. At this point, the right tactic is to research the companies in your outsourcing destination, shortlist the ones providing React.js development services, shortlist them one more time and cut those with no experience in your niche, and finally get in touch with the fitting companies. 

A  worth-partnering company will suggest the best team-gathering option for your project, taking into account your technical requirements, budget expectations, and timelines. 

Conclusion

There are a lot of simple, mid-level, and advanced React.js interview questions you can ask your candidates. Still, make sure to ask them strategically and tailor each of the questions to your project requirements, plus make sure that the programmer is a good fit for your company considering their soft skills and personal traits. A-Team Global can help you with team staffing and team extension so that you can avoid HR management tasks and related burdens.