React js interview questions and Answers

Last updated on Feb 10, 2024
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React js interview questions

ReactJS is a JavaScript library for building reusable User interface components. It is a template-based language combined with different functions that support the HTML. Our recently updated React Interview Questions can help you crack your next interview. This means the result of any React's operation is an HTML code. You can use ReactJS to build all kinds of single-page applications.

Short Questions About React
What is the latest version of React? 18.0, released on March 29, 2022.
When was React first released? 29th May 2013
React JS is Created By Jordan Walke
License of ReactJS MIT License

React Developer Interview Questions

Here in this article, we will be listing frequently asked React js interview questions and Answers with the belief that they will be helpful for you to gain higher marks. Also, to let you know that this article has been written under the guidance of industry professionals and covered all the current competencies.

Q11. What are refs used for in React?

Refs are a function in React having the following uses:

  • Accessing DOM and React elements that you have created.
  • Changing the value of a child component without using props and others.
Q12. How React is different from Angular?
ReactJS AngularJS
This is an open-source JS library used for building user interfaces and uses a controller view pattern. This is a JS-based open-source front end web framework and uses an MVC based pattern.
It is developed and maintained by Facebook Developers. It is developed and maintained by Google Developers.
Based on the JSX programming language. Based on Javascript and HTML language.
It is straightforward to learn. Comparatively, it is difficult to learn.
It supports server-side rendering. It supports client-side rendering.
It has a uni-directional data binding methodology. It has a bi-directional data binding methodology.
It is based on a Virtual DOM. It is based on a regular DOM.

Note: Before getting confused with the plethora of React coding interview questions, you need to ensure the basics. This question will help you to understand the basics of reactjs and make you even more confident enough to jump onto the advanced questions.

Q13. What is the difference between componentWillMount and componentDidMount?
componentWillMount() componentDidMount()
This is called only once during the component lifecycle immediately before the component is rendered to the server. It is used to assess props and do any extra logic based upon them. It is called only on the client end, meaning, it is usually performed after the initial render when a client has received data from the server.
Used to perform state changes before the initial render. It allows you to perform all kinds of advanced interactions including state changes.
No way to “pause” rendering while waiting for the data to arrive. It can be used to set up long-running processes within a component.
It is invoked just immediately after the mounting has occurred. Putting the data loading code in this just ensures that data is fetched from the client's end.
Users should avoid using any async initialization in order to minimize any side-effects or subscriptions in this method. Here, the data does not load until the initial render is done. Hence, users must set an initial state properly to eradicate undefined state errors.
Q14. What is the difference between Function Based Component and Class Based Component?

The Main Difference is of Syntax. The function-Based component used props as an argument and is also called stateless component and In class-based component, we extend all the property of predefined function and used according to our need.

Class Based Component use state and the state is used as props in child component.In Class Based component we can use different lifecycle method of component.

Q15. What are arrow functions? How are they used?

Arrow functions, also called ‘fat arrow‘ (=>), are brief syntax for writing the expression. These functions bind the context of the components because auto binding is not available by default in ES6. Arrow functions are useful if you are working with the higher-order functions.


//General way
render() {
    <MyInput onChange={this.handleChange.bind(this) } />

//With Arrow Function
render() {
      <MyInput onChange={ (e) => this.handleOnChange(e) } />

Q16. What is the purpose of render() in React?

It is compulsory for each React component to have a render(). If more than one element needs to be rendered, they must be grouped inside one tag such as <form>, <group>,<div>. This function goes back to the single react element which is the presentation of native DOM Component. This function must return the same result every time it is invoked.

Q17. What is a state in React and how is it used?

States are at the heart of components. They are the source of data and must be kept simple. States determine components’ rendering and behavior. They are mutable and create dynamic and interactive components, and can be accessed via this.state().

Note: From the vast number of react developer interview questions, answering this will help you to align yourself as an expert in the subject. This is a very tricky question that often makes developers nervous.

Q18. What is the component lifecycle in ReactJS?

Component lifecycle is an important part of ReactJS. Component lifecycle falls into three categories - property updates, Initialization and Destruction. Lifecycle is a method of managing the state and properties of the components.

Q19. What is an event?

Events are the triggered reactions to actions like mouse hover, click, key press, etc.

Q20. What is Redux?

Redux is used to handle data in a reliable manner. It performs task accurately and ensures that the data has been controlled. You can also apply filters if only a specific part of data is required.

NOTE: If you are looking Redux Interview Questions then you can visit here.

Top 20 React.js Interview Questions

Here you will find the list of Top React interview questions, which were written under the supervision of industry experts. These are the most common questions and usually asked in every interview for the role of the React Developers.

  • What is HOC?
  • What are the difference between Rest and Spread Operator?
  • What are the key benefits of using Arrow functions?
  • What is Pure Component?
  • What are Controlled and Uncontrolled components with example?
  • What is Refs?
  • What is the difference between class based component & function based components?
  • How to work React?
  • Why virtual Dom is faster than real dom?
  • How does virtual Dom work in react?
  • What are the difference between null & undefined?


Now that you have read all the react questions, it is time for you to go towards the next level. Applying for a developer position would require you to actually code and not just give answers to theoretical questions.

That’s why you should enhance your skills by complementing the above react developer interview questions with a practical mindset. Start coding small stuff, get your concepts crystal clear. It’s all about how you can apply your knowledge in different projects. Code and code, that’s the secret to winning the dream job!

Reviewed and verified by Umesh Singh
Umesh Singh

My name is Umesh Singh having 11+ experience in Node.JS, React JS, Angular JS, Next JS, PHP, Laravel, WordPress, MySQL, Oracle, JavaScript, HTML and CSS etc. I have worked on around 30+ projects. I lo...