React interview questions to ask (and how an ideal candidate would answer them)

By Robert Half on 18 April 2022
Estimated Read Time: 4 minutes

Although there are hundreds of ideal React interview questions to ask candidates, many focus solely on the technical side of things.

This guide, and sample questions and responses, are aimed at giving you a wholesome approach to the candidate interviewing for a particular role that requires React expertise.

Related: 10 common job interview questions asked in Singapore

What is React?

React is a free and open-source front-end JavaScript library that allows developers to create web applications.

It is important to note that React is a library rather than a language.

A library is a collection of pre-written code that aims to save the user time.

As a result, since it was first released in 2013, React has become one of the most commonly-used front-end libraries for web development.

Related: Examples of Java interview questions

Why React?

Easy to learn

React combines basic HTML and JavaScript concepts to make it easier to create dynamic web applications.

It requires less coding and offers more functionality in comparison to JavaScript, which often gets complex quickly.


React can be used for both web development and for mobile applications.

Since components within React are reusable, developers have the option of adapting them throughout their application, drastically saving time.

Easier debugging

In addition to dedicated tools for debugging, including a Google Chrome extension (released by Meta), React also has the added advantage of unidirectional data flow.

Since the data flows in a single direction, knowing where a problem occurs in an application and how to debug it is considerably easier.

Improved performance

React uses virtual DOM, which saves time and performs significantly better. DOM stands for “Document Object Model,” which represents the user interface (UI) of your application.

Every time there is a change in the UI, the DOM gets updated. Using virtual DOM, changes made are only updated virtually, following which the virtual DOM calculates the best possible way to make these changes in the real DOM.

Related: Have a .NET interview lined up? Here's a guide to answering some common .NET interview questions.

What roles would typically use React?

Some of the roles that would use React include:

  • Front-End Engineers/Developers
  • Web Engineers
  • Web Developers
  • Full-Stack Javascript Engineers/Developers
  • Front-End Leads

Since these roles are considerably varied, more technical React interview questions should be drafted on a case-by-case basis in consultation with a manager with extensive developer knowledge.

Related: Examples of SQL interview questions

Why is it important for hiring managers to ask React interview questions to test a candidate’s knowledge?

Although hiring a developer is an investment, there is a substantially large talent pool from which to choose your future employee.

Testing a candidate’s knowledge is an effective way in mitigating the risk of hiring someone that is not a good fit for a position, as well as establishing a candidate’s experience level.

Ideally, React interview questions should aim to give the candidate an opportunity to convey their strengths and weaknesses without coming off as a quiz that warrants exact definitions.

Here are three versatile React interview questions, why these questions are important and what would a good response be

1. Question: Why did you start using React?

Why this is important: In addition to working across experience levels, this gives the candidate an opportunity to demonstrate their knowledge of React and its advantages. More importantly, this question allows the candidate to talk about any significant projects they have worked on using React.

Response: Benefits of React include higher developer productivity, faster rendering, excellent SEO compatibility, a plethora of developer tool sets, code stability, and strong community support.

2. Question: How do you prevent re-renders in React?

Why this is important: This question gives the candidate an opportunity to explain possible reasons for re-renders in React, as well as how and when to use React shouldComponentUpdate method.

Response: React render is required whenever you are creating a new component. While it’s not bad to re-render multiple components, since React is fast, and efficient at noticing what’s different and what’s not. Re-rendering occurs when the state of the component has been changed. Re-rendering components that are not updated may impact the performance of an application. One option to prevent re-renders is React shouldComponentUpdate, a performance optimisation method that tells React to avoid re-rendering a component. This method can only be used if and when a component will stay static.

3. Question: What are some ways you’d fix a React application that is slow?

Why this is important: This question offers a few possible answers, but also lets you gauge the candidate’s area of expertise.

Response: To successfully optimise a React application, detect a performance problem in the application. Pre-optimisation, measure the application’s performance using the Profiler in the React DevTools. Possible solutions for optimisation might include keeping component state local where possible, Memoizing React components to prevent unnecessary re-renders, code-splitting using dynamic ()import, and even explanations of rendering cycles and virtual DOM.

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