50+ React Interview Questions and Answers
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- Jaro Education
- 30, May 2025
- 11:00 am
React JS has become one of the most popular front-end libraries for web development. Owing to its component-based architecture, extensive support, and efficiency, companies are adopting this platform for front-end development. Hence, the demand for React developers is growing increasingly year-on-year.
So, if you are preparing to enter this world, then knowing some of the important React interview questions and answers is important. It helps you to prepare better and find success, whether you are fresher or experienced.
So, this guide will cover the top React interview questions that you can use to prepare yourself effectively for your React interview.
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React JS Basic Interview Questions
Most of the following React interview questions are aimed at candidates who are new to this domain. It will test your understanding of fundamental concepts.
- What is React?
Facebook developed React to build user interfaces using JavaScript. It is a mechanism to build dynamic web applications by creating and reusing UI components.
- What is JSX?
JSX is a syntax extension added to JS that enables you to write HTML code using JS syntax. Babel then converts it into React elements that are finally rendered to the DOM.
- What is the Virtual DOM in React?
The Virtual DOM is the lightweight representation of real DOM in a memory. It uses it to minimally re-render all the components when some of them have changed.
- What are props in React?
In React, props (stands for properties) are some form of data we can pass to a child component from a parent component. All these are immutable and used to help with communication between components.
- What is the state in React?
It is an object that stores data for components. Meanwhile, the state is maintained within the component itself, and it can be changed using this: setState() in class components or useState() in functional components.
- What is a component in React?
A React application is made up of building blocks referred to as components. They are functional or class-based components for making reusable UI elements.
- What is the difference between state and props in React?
- State is mutable and local to a component, managed within the component itself.
- Props are immutable and passed from parent to child components.
- What is the useState hook in React?
A functional component declares state variables using the useState hook. This returns an array with the current state value as well as a function that you can use to update it.
Example: const [count, setCount] = useState(0);
- What is the purpose of React.Fragment?
It is a wrapper component that helps you group multiple elements without any extra nodes being added to the DOM. This is often used to return several elements from a component without wrapping them in a <div>.
- What are controlled components?
The controlled component is simply a component whose form data is controlled by React’s state. It works with form inputs by using the value and onChange properties.
React JS Interview Questions for Freshers
The following section presents the React JS interview questions for freshers. These React interview questions focused on understanding the basic principles of React JS.
- How do you pass data between components in React?
Props help to pass data from one component to another. The parent component passes data through props for parent-to-child communication.
- What is the role of render() in a class component?
In class components, this render() method is used to determine what should be rendered to the UI. It must return JSX.
- What are function components in React?
Function components are simpler than class components. They are just JavaScript functions that return JSX. If there is no React Hook like useState and useEffect, they do not have their lifecycle state or methods.
- What is the purpose of the useEffect hook?
Using the useEffect hook, you can use side effects inside functional components. It contains data fetching, subscriptions, or even manually changing the DOM.
- What is a React Router?
A standard library for handling routing in React applications is React Router. This allows us to dynamically navigate from one component to another and take care of the URL.
- What are uncontrolled components in React?
The form data of uncontrolled components is manipulated through the DOM. It doesn’t use React state, and the data can be accessed via ref.
- What is the difference between class components and functional components?
- State and lifecycle methods can be added inside Class components.
- Functional components are simpler and don’t have lifecycle methods unless you use hooks like useState and useEffect.
- What is JSX used for in React?
JSX enables you to write HTML using JavaScript syntax. It is used by React to specify how the UI should be.
- What is the useContext hook?
The useContext hook helps you fetch values of the context within the component without manually passing the data from one level of the component tree to another.
- How do you handle events in React?
React handles events using synthetic events, which are normalized to have consistent behavior across different browsers. The components will receive event handlers as props.
React Interview Questions for Experienced Developers
The following React interview questions for experienced developers cover concepts like performance optimization, state management, and routing in this section.
- What is Redux in React?
Redux is a state container used in the context of React. It brings all of your state into a single store and ensures that all of your data flows one way to accomplish this.
- What is the difference between React and Redux?
- Building the UI components is done using the React.
- In React apps, Redux is used to manage and centralize the application state.
- How does React handle lifecycle methods?
There are several lifecycle methods in React in class components such as componentDidMount(), shouldComponentUpdate(), and componentWillUnmount() to run the code at specific points in a component’s life cycle.
- What is a React.memo?
React.memo is a higher-order component that helps you prevent unnecessary re-rendering of a component by remembering its result. It checks the previous and current props and whether the component should be re-render.
- What are React Hooks?
The React Hooks are functions that let you use React state and lifecycle in functional components. Usual hooks include useState, useEffect, and useContext.
- What is the React Context API?
The Context API allows you to share states across the entire app or a tree of components without having to pass props down manually through every level.
- What is React.lazy, and how does it work?
Lazy loading of components is done using React.lazy component, which is used to dynamically import the components when necessary. The code is split, and therefore, the initial load time is reduced.
- What is Concurrent Mode in React?
Concurrent Mode is React’s experimental enhancement that allows the React apps to respond well to the user device capabilities and network speed and work well concurrently so that even if one fails, the ones that succeeded can take over.
- How do you optimize performance in React?
- Use React.memo for functional components.
- Do not use inline functions and objects in render.
- Use React.lazy for code splitting.
- Use libraries like react-window to optimize large lists.
- What is React Suspense?
React Suspense is a part of the React API that deals with asynchronous operations like code splitting and data fetching by delaying the rendering of the component until some conditions are met.
- What are higher-order components (HOCs)?
The higher-order component (HOC) is a function that accepts a component and returns a new component with extra props or functionality. It is used for code reuse and enhancing the behavior of components.
- How do you manage side effects in React?
In React, side effects such as fetching data or manipulating the DOM can be handled through the useEffect hook in the functional component or lifecycle method of the class component.
- What is Server-Side Rendering (SSR)?
Server Side Rendering (or SSR for short) is the process of selecting page views of a React App being rendered on the server. It improves the initial page load speed and increases SEO rank.
- What are React Fragments?
Using React Fragments, you can group a number of elements without creating extra nodes for the DOM. It is often used to return multiple elements from a component.
- What is memoization in React?
Memoization is a technique of optimization to avoid unnecessary recalculation. There are React.memo and useMemo in React, through which you can memoize the components or values.
- What are Error Boundaries in React?
Error Boundaries are Components that catch JavaScript errors happening in their children components, log the error and present a fallback UI.
- What is Hydration in React?
Hydration is the attaching of event listeners and the initialization of the state of server-rendered HTML, allowing it to be interactive in the client browser.
- What is the useCallback hook?
The useCallback hook is used to memoize functions such that they do not get recreated when the render is called, and it helps to optimize the performance in React apps.
- What is a React Router?
React Router is a routing library for React that enables you to declare the navigation and URL manipulations of your React application.
- How do you handle form validation in React?
Validation in React form can be done using state managing and conditional rendering. In the case of more complex forms, you can use libraries such as Formik and React Hook Form.
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Advanced React Interview Questions
If you have some experience with React and also some other technologies, these advanced React interview questions are designed for you:
- What is React Fiber?
React Fiber is the complete rewrite of the React core algorithm for better rendering performance. It also supports advanced features like Concurrent Mode.
- What is Lazy Loading in React?
React lazy loading is loading components only when they are required, not all the components at a time. To make this possible, React.lazy() and Suspense can be used.
- What is the useReducer hook in React?
The useReducer is another way to manage complex state logic in React applications. It works similarly to how Redux handles state updates.
- What are memoization techniques in React?
In React, memoization techniques such as React.memo, useMemo, and useCallback can be used to optimize your performance by curbing unnecessary re-rendering and recalculation.
- How does React handle event delegation?
React uses event delegation by attaching a single event listener at the root of the DOM and dispatching the event to the right component.
- What is Code Splitting in React?
Code splitting is an idea to separate your application into smaller bundles that can be loaded only when required, accelerating the initial load time.
- What is the purpose of Context API in React?
The Context API allows you to share values such as a theme, authentication data, or language preference among the component tree without manually passing props.
- What is the useLayoutEffect hook?
The useLayoutEffect hook has an identity similar to useEffect, but it runs after all DOM mutations, with a sync before the browser repaints.
- What is React Concurrent Mode?
Concurrent Mode is an experimental feature that allows React apps to remain responsive by adjusting to varying device capabilities and network speed.
- How do you optimize the performance of a large React app?
- Code splitting with React.lazy
- Memoization using useMemo and useCallback
- Avoid unnecessary renders with React.memo
- Hosting on the server and implementing lazy loading and server-side rendering (SSR)
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Conclusion
React interview questions can be both exciting as well as challenging, but with the right preparation with the help of the core concepts, you can approach any question that you come across with confidence. If you have little or no experience with React, you can go through the above-mentioned React interview questions and answers in this blog to become acquainted with the basic stuff before your interview to make sure you excel in it.
This guide covers the basics of JSX, props, and state and also goes into the deeper topics like React hooks, Redux, and React Router, so you have everything you need for an encounter with a React interviewer. Knowing React JS interview questions for freshers and React interview questions for experienced developers will help you get the upper hand over the other candidates during the interview and use it to pitch yourself at any designation.
Remember, a solid understanding of React fundamentals, performance optimization techniques, and best practices will prevent you from being overlooked in interviews. Thus, keep practicing, be aware of the latest React features, and be prepared to show your problem-solving skills with real-life examples.
Best of luck with the preparation of the interview, and don’t forget to learn and continue to build your React skills.
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