Top 10 React JS Interview Questions for Hiring React JS Developers

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By: Manish Shewaramani

Top 10 React JS Interview Questions to ask before you hire React JS Developer (for React JS Development)

Searching for an appropriate React JS development company can be challenging. The reasons are that every React JS development project is different, and so are the development firms.

The first step for you should be to define a clear statement of requirements. Then you should look for a firm that has developers who have all the capabilities and skills to take up your project.

Preparing React JS interview questions and asking them to developers is one of the best ways to check their skills. However, the best-case scenario would be to ask them to create a small prototype. It will help you to judge a developer more accurately.

10 React JS Interview Questions to ask before Hiring a Development Company

Below mentioned React JS interview questions are the ones which every developer who has worked with React JS should know. This article is written from the perspective of a person looking to hire React JS developer for a web development project.

Q1 – Tell me something about your previous jobs, responsibilities, and projects

Knowing about the previous jobs and responsibilities of a developer will help you identify whether the person has done anything that you require in your current project.

It will give you an overview of a developer. You’ll also get to know the soft skills he or she possesses. Whether he/she has work in teams or not? You’ll also get to know the impact (created an app used by 1 million users today) he/she brought by his/her hard skills.

Q2 – Why did you decide to go with React and not the other frameworks?

Here instead of looking for answers like ” because of Virtual DOM, JSX, etc.”, you should look for answers like “I learned React because it was easy to learn, but challenging to master.”

This will help you identify the learning attitude of a developer. He/she will be willing to learn more if your project demands.

Answers like “because of better job opportunity” will make him/her an excellent choice for hire since React is going to dominate front-end development for at least five years.

Q3 – What is JSX and how can it be written in our JavaScript code. How does the browser recognize the code?

The reason behind asking this question is that a React developer must know the technical side of JSX along with its various shortcomings. He/she should know even the smallest elements of JSX.

Developers must know that the reason why Component names in JSX start with a capital letter because it helps React differentiate between components and HTML elements.

Q4 – What are the major two types of components that can be declared in React, and when should you use one over the other?

The true answer to this question is that instead of presentation and container components, it is more about function components and React.Component.

The correct answer should mention component state and lifecycle methods.

Q5 – Now that we have mentioned lifecycle, can you tell me the cycle of mounting a stateful component? In what order are the function called? Where could you place a request for data from the API and why?

In this question, make sure that you expect the developers to explain the changes that happened in the life cycle in recent months and not the life cycle itself.

If you get the answers such as “componentsWillMount,” then you can assume that the developer has been working with either the outdated version of React or he/she has gone through the outdated tutorials. The answer you should expect is “getDerivedStateFromProps.”

You must give bonus points to the developer who gives you the differences in the way the process goes on server-side.

Q6 – How can you make sure that the data is not re-fetched when the component is remounted?

This question is not entirely related to React. People who have worked with GraphQL might know the answer to this question.

This question helps you to judge whether the person you want to hire knows the idea of not-coupling the UI and other layers in the app. However, they can mention the API that is external to the React structure.

Q7 – Can you elaborate on the idea of “lifting the state up?”

Although it is one of the typical React JS interview questions, it is still worth asking.

You can expect answers such as “It allows you to pass the data between siblings” or “It allows you to have several pure-presentational components, which increases re-usability.”

If you get the answer as Redux, then you can assume that the candidate blindly follows the community recommendations without understanding its requirements in the project.

Q8 – In a React code, how would you debug a code? Which tools will you use and how would you investigate the reason for not re-rendering of a component?

The tools you should expect a developer to use our linter (eslint, jslint) and debugger (React Developer Tools).

You can expect answers like “I use RDT to debug the issue by checking if the component props/state are set properly” or “I use RDT to setup breakpoints.”

Q9 – What tools do you use for unit testing?

Here, you can expect a developer to name tools such as mocha, karma, jest, jasmin, selenium, enzyme, cypres, react-test-library, and more. Perhaps the worst answer could be “I don’t do unit testing. I only do manual testing.”

Q10 – What were the biggest challenges that you have faced on your previous projects, and what were your greatest achievements?

For this question, the answer can vary from developer to developer. A junior developer might say that he/she was thrown into solving a complex issue and conquered it.

Senior developers might explain how they optimized the performance of an app. Whereas, team leaders might explain how they finished a project before time with fantastic teamwork.

Final Words

The React JS interview questions mentioned above are the ones which give an overview of a React JS developer. However, if you want to choose the most appropriate developers, you can always ask questions specific to your project and requirements.

If you have a React JS project idea in mind, contact our experts who will help you from consultation to deployment to post-release support.

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