React JS Interview Questions to Ace Your Job in 2025

Why are React JS Skills in High Demand?

The popularity of React JS skills can be attributed to the numerous features and benefits the library serves. Its flexibility, scalability, and ease of creating dynamic user interfaces increase its applications among the companies, thus enhancing the skilled personnel requirements. React JS offers advantages such as virtual DOM for rendering, component-based architecture, an easy learning curve and broad community support. Further, the library provides fast rendering, code reusability and maintainability, a rich ecosystem and SEO-friendly development. Also, its usage is witnessed in well-known software such as Facebook, Netflix and Discord.

Most Asked ReactJS Interview Questions

1. What is ReactJS?
2. Why ReactJS is Used?
3. How Does ReactJS work?
4. What are the features of ReactJS?
5. What is JSX?
6. How to create components in ReactJS?
7. What are the advantages of ReactJS?
8. Differentiate between real DOM and virtual DOM?
9. What are forms in ReactJS?
10. How is React different from React Native?

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Basic ReactJS Interview Questions

Master the basics of React components, state, props, and more to build a solid foundation with these basic ReactJS interview questions and answers.

1. What are the features of React?

	JSX: JSX is a syntax extension to JavaScript. It is used with React to describe the user interface's appearance. Using JSX, we can write HTML structures in the same file that contains JavaScript code.
	Components: Components are the building blocks of any React application, and a single app usually consists of multiple components. It splits the user interface into independent, reusable parts that can be processed separately.
	Virtual DOM: React keeps a lightweight representation of the real DOM in memory, known as the virtual DOM. When an object's state changes, the virtual DOM changes only that object in the real DOM rather than updating all the objects.
	One-way data-binding: React’s one-way data binding keeps everything modular and fast. A unidirectional data flow means that when designing a React app, you often nest child components within parent components.
	High performance: React updates only those components that have changed rather than all the components simultaneously, resulting in faster web applications.

2. What is JSX?

JSX is a syntax extension of JavaScript. It is used with React to describe the user interface's appearance. Using JSX, we can write HTML structures in the same file that contains JavaScript code.

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3. Can web browsers read JSX directly?

• Web browsers cannot read JSX directly. They are built only to read regular JS objects, and JSX is not a regular JavaScript object. 
• A web browser can only read a JSX file if transformed into a regular JavaScript object. We use Babel for this.

4. What is the virtual DOM?

DOM stands for Document Object Model. It represents an HTML document with a logical tree structure. Each branch of the tree ends in a node, which contains objects.

React keeps a lightweight representation of the real DOM in memory, known as the virtual DOM. When an object's state changes, the virtual DOM changes only that object in the real DOM rather than updating all the objects. The following are some of the most frequently asked react interview questions.

5. Why use React instead of other frameworks, like Angular?

• Easy creation of dynamic applications: React makes it easier to create dynamic web applications because it requires less coding and more functionality, whereas code tends to get complex very quickly with JavaScript applications.
• Improved performance: React uses virtual DOM, which makes web applications perform faster. Virtual DOM compares its previous state and updates only those components in the real DOM, whose states have changed, rather than updating all the components — like conventional web applications.
• Reusable components: Components are the building blocks of any React application, and a single app usually consists of multiple components. These components have logic and controls and can be reused throughout the application, dramatically reducing development time.
• Unidirectional data flow: React follows a unidirectional data flow. When designing a React app, we often nest child components within parent components. Since the data flows in a single direction, debugging errors and knowing where the problem occurs in an application become easier.
• Dedicated tools for easy debugging: Facebook has released a Chrome extension for debugging React applications. This makes the process of debugging React web applications faster and easier.

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6. What is the difference between the ES6 and ES5 standards?

These are the few instances where ES6 syntax has changed from ES5 syntax:

• Components and Function

• exports vs export

• require vs import

7. How do you create a React app?

These are the steps for creating a React app:

• Install NodeJS on the computer. We need NPM to install the React library. Npm is the Node package manager with many JavaScript libraries, including React.

• Install the create-react-app package using the command prompt or terminal.

• Install a text editor you choose, like VS Code or Sublime Text.

8. What is an event in React?

An event is an action a user or system may trigger, such as pressing a key or clicking a mouse.

• React events are named using camelCase rather than lowercase in HTML.
• With JSX, you pass a function as the event handler rather than a string in HTML.

9. How do you create an event in React?

A React event can be created by doing the following:

10. What are synthetic events in React?

• Synthetic events combine the response of different browsers' native events into one API, ensuring consistency across browsers.
• The application is consistent regardless of the browser in which it is running. Here, preventDefault is a synthetic event.

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11. Explain how lists work in React.

• We create lists in React as we do in regular JavaScript. Lists display data in an ordered format.
• The traversal of lists is done using the map() function.

12. Why is there a need to use keys in Lists?

Keys are vital in lists for the following reasons:

• A key is a unique identifier, and it is used to identify which items have changed, been updated or deleted from the lists
• It also helps to determine which components need to be re-rendered instead of re-rendering all the components every time. Therefore, it increases performance, as only the updated components are re-rendered.

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13. What are forms in React?

React employs forms to enable users to interact with web applications.

• Using forms, users can interact with the application and enter the required information whenever needed. Form contains certain elements, such as text fields, buttons, checkboxes, radio buttons, etc.
• Forms are used for many tasks, such as user authentication, searching, filtering, indexing, etc.

14. How do you create forms in React?

We create forms in React by doing the following: 

The above code will yield an input field with the label Name and a submit button. It will also alert the user when the submit button is pressed.

15. How do you write comments in React?

There are two ways in which we can write comments:

• Single-line comments

• Multi-line comments

16. What is an arrow function and how is it used in React?

• An arrow function is a short way of writing a function to React.
• It is unnecessary to bind ‘this’ inside the constructor when using an arrow function. This prevents bugs caused by the use of ‘this’ in React callbacks.

17. How is React different from React Native?

18. How is React different from Angular?

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19. What are React Hooks?

React Hooks are functions introduced in React 16.8 that allow you to use state and lifecycle features in functional components. Hooks like useState, useEffect, and useContext make it easier to manage component logic without using classes, improving readability and reusability.

20. What is useState, and how does it work?

useState is a hook that allows you to add state to functional components. It takes an initial state value and returns an array with two elements: the current state and a function to update it. useState re-renders the component when the state is updated.

21. What is useEffect, and how does it differ from lifecycle methods in class components?

useEffect is a hook for performing side effects in functional components, like fetching data or setting up subscriptions. It combines the behavior of componentDidMount, componentDidUpdate, and componentWillUnmount in class components, allowing effects to run after render and clean up when dependencies change.

22. What is Memoization in React?

Memoization is an optimization technique that saves the result of expensive function calls and reuses it when the same inputs occur. React.memo and useMemo prevent unnecessary re-renders and calculations by caching results based on dependencies.

23. What is Prop Drilling and how do you avoid it?

Prop drilling occurs when props are unnecessarily passed through multiple component layers to reach a nested component. You can avoid it using Context API, which allows you to share the state between deeply nested components without manually passing props down.

React JS Interview Questions for Freshers

For beginners, practice the following React JS interview questions for freshers for interview and concept clarification:

24. Explain React JS to a person with no programming experience.

React JS is a library for user interface development. It holds applications that allow users to manage the visual layout of web pages across different devices. The library is generally linked with Single-Page applications but also witnesses applications across multiple-page applications. It is also used for mobile app development in both Android and iOS.

25. State the limitations of React.

Some of the restrictions in using React include the lack of a complete framework, the large number of components in React, and the complexity of coding, which adds to challenges for new learners.

26. State the use of webpack.

The webpack refers to the command line tool. It is used to gather the application’s dependencies, such as distinct code files and assets, into a large, single and static file. Webpack minimizes JavaScript, images, CSS files and others. The webpack allows developers to modularize the code for enhanced readability via loaders, entry points and plugins.

27. Differentiate between controlled and uncontrolled components. 

The controlled components involve enforced input format, field-level validation, the ability to conditionally turn off the submit button, multiple inputs for specific data and dynamic inputs, which are absent from the uncontrolled components. Further, React controls the input value. 

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28. Define Custom Hooks. 

Custom Hooks refer to the function beginning with ‘use.’ Available in JavaScript, they call other hooks. Custom Hooks allow repeated use of stateful logic without requiring a restructuring of the component hierarchy. 

29. What is a dispatcher? 

Dispatcher is a function in React JS that sends an action to the store to trigger a state update. It acts as a central hub and sent actions are processed by reducers.

30. State the different side effects of the React component.

There are two side effects in React: one with cleanup and the other without. The side effects of cleanup require effect cleanup after an operation to avoid memory leaks or unwanted behaviors. The side effects without cleanup do not require component cleanup. They include actions like component state updates, data fetching or API calls.

31. What are the lifecycle steps in React?

The lifecycle steps in React include initialization, state or property updates and destruction. Initialization involves creating components; the second step involves re-rendering them during a state or property change. Destroying involves removing components from the UI and performing the necessary cleanup.

32. What do you understand by error boundaries? 

The error boundaries allow errors to be caught inside the constructor and lifecycle method during the render phase. It refers to the component capable of catching errors. 

33. State the rules to follow when using React Hooks. 

Users must follow two rules. The first is to call the React Hook specifically at the top level. It should not be called inside loops, nested functions or conditions. The second rule is that the React Hook must be called from the React Function Components only.

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ReactJS Interview Questions on Components

Explore essential ReactJS interview questions on components, covering key concepts like props, state, lifecycle methods, and functional vs. class components.

34. What are the components in React?

Components are the building blocks of any React application, and a single app usually consists of multiple components. A component is essentially a piece of the user interface. It splits the user interface into independent, reusable parts that can be processed separately.

There are two types of components in React:

• Functional Components: These components have no state and only contain render methods. Therefore, they are also called stateless components. They may derive data from other components as props (properties).

function Greeting(props) {
  return <h1>Welcome to {props.name}</h1>;
}

• Class Components: These components can hold and manage their state and have a separate render method to return JSX on the screen. They are also called Stateful components, as they can have a state.

class Greeting extends React.Component {
  render() {
    return <h1>Welcome to {this.props.name}</h1>;
  }
}

35. What is the use of render() in React?

render() is a lifecycle method in class components that returns the JSX to be displayed on the screen. It’s called every time the component’s state or props change, updating the UI accordingly.

36. What is a state in React?

• The state is a built-in React object that contains data or information about the component. A component's state can change over time, and whenever it changes, the component re-renders.
• The state change can occur as a response to user action or system-generated events. It determines the component's behavior and rendering method.

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37. How do you implement state in React?

38. How do you update the state of a component?

We can update the state of a component by using the built-in ‘setState()’ method:

39. What are props in React?

Props (short for properties) are inputs passed from parent to child components, allowing data and configuration to flow into the component. Props are read-only and cannot be modified within the child component.

40. How do you pass props between components?

Props are passed from a parent to a child component by including them as attributes in the child component's JSX tag. The child component then accesses the props through props.propertyName.

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41. What are the differences between state and props?

State is a local, mutable data structure managed within a component, whereas props are immutable data passed from a parent to a child component. State is used for dynamic data within the component, while props control component behavior from outside.

42. What is a higher-order component in React?

A higher-order component (HOC) is a function that takes a component and returns an enhanced component, adding functionality or modifying behavior. HOCs are used for cross-cutting concerns like authentication, logging, or data fetching.

43. How can you embed two or more components into one?

You can embed components by nesting them within a parent component or using composition to render multiple components together. You can also pass components as children or props for dynamic embedding.

44. What are the differences between class and functional components?

Class components use ES6 classes and provide access to lifecycle methods and state via this.state. Functional components are simpler, using functions to define components and accessing state and lifecycle features through hooks like useState and useEffect.

• Class components example:

• Functional components example:

45. Explain the lifecycle methods of components.

• getInitialState(): Is executed before the creation of the component.
• componentDidMount(): Is executed when the component gets rendered and placed on the DOM.
• shouldComponentUpdate(): Is invoked when a component determines changes to the DOM and returns a “true” or “false” value based on certain conditions.
• componentDidUpdate(): Is invoked immediately after rendering takes place.
• componentWillUnmount(): Is invoked immediately before a component is destroyed and permanently unmounted.

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React JS Interview Questions for Experienced

The candidates' holding experience with the library, here are some React JS interview questions and answers for you to practice:

46. Describe the lifting state up in React. 

Lifting state up in React refers to a technique. It allows state sharing among multiple components by moving the state from individual components to their parent and passing it down to the component. This technique helps synchronize the data across the components.

47. How do we avoid binding in React JS? 

Binding can be avoided using the arrow function in React JS, as it lacks its own ‘this’ content and offers cleaner syntax.

48. Explain React fragments.

The library's React fragment feature ensures the return of multiple elements from the React component. It does so by grouping a list of children without the requirement to add nodes in the DOM. Fragments do not add additional makeup to rendered HTML, so they are also lightweight.

49. When should you use useMemo() in React?

The useMemo() in React is used to perform expensive calculations and for referential equality. The latter includes passing complex objects as a prop to a child component.

50. What are the different types of Hooks in React?

There are two broad types of hooks in React: built-in and custom hooks. The built-in hooks are further of two types: basic and additional hooks. Examples of basic hooks are useState(), useContext() and useEffect(), while an example of additional hooks is useMemo(), useRef() and others. The Custom Hook is a JavaScript function that works similarly to a regular function.

51. State the different lifecycle methods in the updating phase.

The lifecycle methods in the updating phase are as follows: ComponentWillReceiveProps, Render, ComponentDidUpdate, ShouldComponentUpdate and ComponentWillUpdate.

52. Enlist the functions of high-order components.

Some functions of high-order components or HOC include rendering hijacking, conditional rendering, manipulating props, enhancing component behavior, logic encapsulation and manipulating and reusing code.

53. What do you understand by three dots in React in the syntax <Image{...aspects} source=’img_source”>

The three dots in React refer to the spread operator or spread syntax, an ES6 feature used in React. Spread syntax deconstructs arrays or objects into separate variables. It also encourages array expressions or string expansions at locations expecting zero or more arguments or key-value pairs.

54. What is the strict mode in React?

React Strict Mode is the tool for identifying and fixing issues in the code. It contributes to the enhancement of code quality by providing warnings. The strict mode can be enabled in React by wrapping the complete application via the <StrictMode> component.

55. State the components of the React router. 

The key components of a React router include a Router, switch, route and link. The router is the parent component that stores all other components. The switch component is used to render only the first route, the route component checks the existing URL, and the link component develops links to varying types of routes.

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ReactJS Redux Interview Questions

Prepare for your next interview with essential ReactJS Redux questions covering key concepts like state management, actions, reducers, and middleware.

56. What is Redux?

Redux is a state management library for JavaScript applications, often used with React. It centralizes the application’s state in a store, allowing components to access and update the state through actions and reducers.

57. What are the components of Redux?

Redux has three main components: the store (which holds the application state), actions (which describe what to do), and reducers (which define how the state changes in response to actions).

58. What is the Flux?

• Flux is an application architecture pattern for managing data flow. Actions are dispatched to stores, which then update views. It’s commonly used with React to ensure a unidirectional data flow.

• There is a single source of data (the store), and the only way to update it is to trigger certain actions. The actions call the dispatcher, and the store is triggered and updated with its data.

• When a dispatch has been triggered and the store updates, it emits a change event that allows the views to re-render accordingly.

59. How is Redux different from Flux?

Both Redux and Flux are state management architectures, but Redux has a single store, while Flux uses multiple stores. Redux also enforces immutability and provides middleware like Redux Thunk for asynchronous actions.

60. What is the difference between Context API and Redux?

Context API is a simpler way to share state across components without prop drilling and is suitable for less complex applications. On the other hand, Redux is more robust, with middleware and a global store, making it better for complex, scalable state management.

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ReactJS Router Questions

Here are the key ReactJS Router questions that test your understanding of navigation, routing, and dynamic rendering in single-page applications.

61. What is React Router?

React Router library adds navigation and routing to single-page React applications. It lets you define routes and navigate between different components without reloading the page.

62. Why do we need to React Router?

React Router allows seamless navigation in a single-page application (SPA) by managing URL changes without refreshing the page, improving user experience and enabling multi-view applications.

63. How is React routing different from conventional routing?

Traditional routing reloads the page on each navigation, while React routing dynamically loads components within the same page, creating a faster, SPA-like experience.

64. How do you implement React routing?

To implement React routing, install react-router-dom, define routes using Route and Switch components, and use Link or NavLink to navigate between them without reloading the page.

Considering we have the components App, About, and Contact in our application:

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ReactJS Styling Interview Questions

Here are some ReactJS Interview Questions on the Styling concept of ReactJS.

65. How do you style React components?

React components can be styled with CSS, inline styles, styled components, or CSS-in-JS libraries. You can also use frameworks like Material-UI or Bootstrap for pre-built styles.

• Inline Styling

• JavaScript Object

• CSS Stylesheet

66. Explain the use of CSS modules in React.

CSS modules are scoped CSS files that apply styles locally to components, preventing naming conflicts. In React, you can import CSS modules and use them as objects, allowing you to create modular, maintainable styles.

Tips for Success in a React JS Interview

Here are some tips to help you land the opportunity by making an impression in the interview: 

• Practice coding questions 
• Enhance communication skills 
• Research the company and thoroughly understand the job description 
• Prepare the interview questions and answers. It helps by revising the forgotten aspects and offering familiarity with the questions
• Give mock interviews to have a habit of verbally framing answers 
• Be updated with the latest information about React JS
• Discuss projects and add personalized and experience-based information 
• Put forward thoughtful questions after the interview, such as those based on team dynamics and organizational development methodologies

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Conclusion

We hope this article helped you better understand the different ReactJS interview questions that can be asked and help you prepare for them. To further enhance your software development skills, we highly recommend you check out Simplilearn's Full Stack Developer - MERN Stack Course. This program can help you hone the right skills and make you job-ready quickly.

Preparing for a ReactJS interview involves understanding the intricacies of this popular JavaScript library and ensuring that your user interface (UI) design skills are up to par. ReactJS is widely used for building dynamic and interactive user interfaces, making a strong grasp of UI design principles crucial for creating engaging web applications.

FAQs

1. What is the difference between React and Angular?

React is a JavaScript library, while Angular is a framework. React uses one virtual DOM and one-way data binding and has a small bundle size. Conversely, Angular uses real DOM and two-way data binding and is lighter and faster. 

2. What are some common mistakes made by React developers during interviews?

Some common mistakes React developers make include overusing setState, poor coding practices, not using key props, and error handling and cleanup in useEffect. 

3. What are the most important React concepts to focus on for interviews?

Lifecycle methods, state, components, performance optimization, and event handling are key concepts that must be considered when preparing for the React interview.

4. How can I practice React coding challenges effectively?

Building simple projects, solving coding challenges on websites like Codewars, LeetCode and others and reading other people’s codes are effective ways to practice React coding.