React Coding Interview Questions and Answers (2025)

React has become one of the most in-demand frameworks for frontend interviews. Companies of every size, from startups to tech giants, use it to build fast, interactive, and scalable user interfaces. Because of this, React is now a key focus in many technical interviews.

If you’re preparing for a coding interview using React, the right preparation will set you apart. Interviewers aren’t just looking for candidates who can write React code. They want to know whether you understand how React works under the hood. That’s why React coding interview questions often cover a wide range of topics, from basic component structure to advanced optimization techniques.

By the end of this guide, you’ll have a clear, step-by-step understanding of how to answer the most common React coding interview questions with confidence.

Why React Is a Popular Choice in Coding Interviews

React continues to dominate the frontend development space, which makes it a natural choice to practice for coding interviews. There are several reasons why interviewers focus so heavily on React.

React powers some of the world’s most popular applications, from Facebook and Instagram to Airbnb and Netflix. Its widespread adoption means employers want candidates who can hit the ground running with React.

With React, you can build everything from single-page web applications (SPAs) to large enterprise dashboards. Pair it with React Native, and you can even build mobile apps with the same skills. This versatility makes it attractive to companies looking for adaptable engineers.

React also has one of the largest ecosystems in frontend development. Libraries for state management (like Redux or Zustand), testing tools, and performance utilities are widely available and well-supported. Knowing React means you can leverage this ecosystem effectively.

In short, React is popular in interviews because it combines demand, flexibility, ecosystem support, and practical application, which is everything employers value.

Categories of React Coding Interview Questions

React interview prep becomes easier once you know the main categories of questions. Each category tests a different skill, from foundational concepts to advanced techniques.

Here are the most common categories of React coding interview questions:

React fundamentals (JSX, components, props, state): Tests your ability to build the core building blocks of React apps.
Component lifecycle methods: Covers how class components manage mounting, updating, and unmounting, and how hooks replace them.
Hooks (useState, useEffect, useContext, custom hooks): One of the most tested areas—interviewers want to know if you can manage side effects and state efficiently.
State management (Redux, Context API): Evaluates whether you can handle complex state across multiple components.
Event handling and forms: Focuses on user input, form validation, and controlled vs uncontrolled components.
React Router and navigation: Tests your ability to manage routes, dynamic parameters, and protected pages.
Performance optimization: Includes React.memo, useMemo, useCallback, and techniques like lazy loading.
Testing in React (Jest, React Testing Library): Ensures you can write testable, maintainable components.
Advanced topics: Covers error boundaries, portals, concurrent rendering, and server-side rendering (SSR).
Mock practice questions: Hands-on exercises that combine multiple concepts.

By preparing across these categories, you’ll cover everything from beginner-level syntax to senior-level architecture. This structure ensures you won’t be caught off guard in interviews.

Basic React Coding Interview Questions

Before diving into hooks or optimization, interviewers want to see if you’ve mastered the fundamentals. Many React coding interview questions start with these basics before moving into advanced topics.

1. What is JSX, and why is it used?

Explanation:

JSX (JavaScript XML) is a syntax extension that lets you write HTML-like code inside JavaScript. React uses JSX to make UI structures more readable.

Code Example:

const element = <h1>Hello, React!</h1>;

Sample Answer:

“JSX is a syntax extension that allows you to write HTML-like code in JavaScript. It makes components more readable and is compiled into React.createElement calls under the hood.”

2. Difference between functional and class components

Explanation:

Functional components: Plain JavaScript functions that return JSX. Modern React favors functional components with hooks.
Class components: ES6 classes that extend React.Component and use lifecycle methods.

Code Example:

function Greeting() {

  return <h1>Hello</h1>;

}

class GreetingClass extends React.Component {

  render() {

    return <h1>Hello</h1>;

  }

}

Sample Answer:

“Functional components are simpler and can use hooks. Class components use lifecycle methods and are less common in modern React.”

3. What are props in React?

Explanation:

Props (short for properties) are read-only inputs passed from parent to child components.

Code Example:

function Welcome(props) {

  return <h1>Hello, {props.name}</h1>;

}

Sample Answer:

“Props allow data to be passed into components. They’re immutable, meaning a child cannot change its props.”

4. How is state different from props?

Explanation:

Props: External, passed from parent.
State: Internal, managed within a component.

Code Example:

function Counter() {

  const [count, setCount] = React.useState(0);

  return <button onClick={() => setCount(count + 1)}>{count}</button>;

}

Sample Answer:

“Props are passed into a component and are immutable. State is internal and can change over time, triggering re-renders.”

5. Explain virtual DOM and how React uses it

Explanation:

The virtual DOM is a lightweight in-memory representation of the real DOM. React compares the virtual DOM with the previous version (diffing) and updates only what has changed.

Code Example:

// React updates only changed nodes

<div>

  <h1>Hello</h1>

  <p>Updated text</p>

</div>

Sample Answer:

“React uses a virtual DOM to make updates efficient. Instead of re-rendering the entire page, it updates only the parts that change.”

These basic concepts are essential. Many React coding interview questions start with JSX, props, state, and the virtual DOM before moving into hooks, routing, and optimization.

Component Lifecycle Methods

Class components in React follow a lifecycle with distinct phases. Many React coding interview questions test whether you understand these methods and how they map to modern hooks.

1. What are the phases of a React component lifecycle?

React class components have three main phases:

Mounting: When the component is first added to the DOM.
Updating: When props or state change.
Unmounting: When the component is removed from the DOM.

Each phase has lifecycle methods like componentDidMount, componentDidUpdate, and componentWillUnmount.

2. Difference between componentDidMount, componentDidUpdate, and componentWillUnmount

class Example extends React.Component {

  componentDidMount() {

    console.log(“Mounted”);

  }

  componentDidUpdate(prevProps, prevState) {

    console.log(“Updated”);

  }

  componentWillUnmount() {

    console.log(“Unmounted”);

  }

}

componentDidMount: Runs once after the component mounts. Perfect for fetching data.
componentDidUpdate: Runs after every update. Useful for reacting to state or prop changes.
componentWillUnmount: Runs before removal. Use it for cleanup, like unsubscribing from events.

3. How do you fetch data in lifecycle methods?

class Users extends React.Component {

  state = { users: [] };

  componentDidMount() {

    fetch(“/api/users”)

      .then(res => res.json())

      .then(data => this.setState({ users: data }));

  }

  render() {

    return <ul>{this.state.users.map(u => <li key={u.id}>{u.name}</li>)}</ul>;

  }

}

Answer: Data fetching is usually done in componentDidMount to ensure the component is ready.

4. Why were lifecycle methods replaced by hooks?

Lifecycle methods were powerful but often caused duplicated logic and complexity. Hooks like useEffect let you handle side effects in functional components, making the code cleaner and reusable.

Even though hooks are the standard, many React coding interview questions still ask about lifecycle methods. It’s important to know both class-based and hook-based approaches.

React Hooks in Coding Interviews

Hooks are one of the most common topics in React interviews. They simplify state and side effect management in functional components.

1. What is useState and how does it work?

function Counter() {

  const [count, setCount] = React.useState(0);

  return <button onClick={() => setCount(count + 1)}>{count}</button>;

}

Answer: useState lets you add state to functional components. It returns an array with the current state and a setter function.

2. How does useEffect replace lifecycle methods?

function Timer() {

  React.useEffect(() => {

    const interval = setInterval(() => console.log(“tick”), 1000);

    return () => clearInterval(interval);

  }, []);

}

Answer:

Replaces componentDidMount (run on mount).
Replaces componentDidUpdate (run on update when dependencies change).
Replaces componentWillUnmount (cleanup in return function).

3. Explain useContext with an example

const ThemeContext = React.createContext(“light”);

function App() {

  return (

    <ThemeContext.Provider value="dark">

      <Button />

    </ThemeContext.Provider>

  );

}

function Button() {

  const theme = React.useContext(ThemeContext);

  return <button className={theme}>Click me</button>;

}

Answer: useContext provides access to values from a Context without prop drilling.

4. What are custom hooks and when should you use them?

function useWindowWidth() {

  const [width, setWidth] = React.useState(window.innerWidth);

  React.useEffect(() => {

    const handleResize = () => setWidth(window.innerWidth);

    window.addEventListener(“resize”, handleResize);

    return () => window.removeEventListener(“resize”, handleResize);

  }, []);

  return width;

}

Answer: Custom hooks let you reuse logic across components. They’re just functions that use other hooks.

5. Difference between useMemo and useCallback

useMemo: Memoizes values.
useCallback: Memoizes functions.

const memoizedValue = React.useMemo(() => expensiveCalc(num), [num]);

const memoizedFn = React.useCallback(() => handleClick(value), [value]);

Hooks are central to modern React. Most React coding interview questions include useState, useEffect, and optimization hooks like useMemo and useCallback.

State Management: Redux and Context API

When apps grow, managing state becomes complex. That’s why state management tools are heavily tested.

1. What problem does Redux solve?

Redux solves prop drilling and keeps application state predictable. It centralizes state into a single store.

2. Explain actions, reducers, and the store

// Action

const increment = { type: “INCREMENT” };

// Reducer

function counter(state = 0, action) {

  switch (action.type) {

    case “INCREMENT”: return state + 1;

    default: return state;

  }

}

// Store

import { createStore } from “redux”;

const store = createStore(counter);

Answer:

Actions: Describe events.
Reducers: Pure functions that update state.
Store: Holds global state.

3. Difference between Redux and Context API

Redux: Predictable state container with middleware and debugging tools. Best for large apps.
Context API: Good for smaller apps to avoid prop drilling.

4. When should you use Redux over Context?

Use Redux when:

The app is large and has complex state logic.
You need middleware like Redux Thunk for async actions.
You need powerful dev tools.

5. How does middleware like Redux Thunk work?

Redux Thunk lets you write async logic in action creators.

function fetchUsers() {

  return dispatch => {

    fetch(“/api/users”)

      .then(res => res.json())

      .then(data => dispatch({ type: “SET_USERS”, payload: data }));

  };

}

Many React coding interview questions focus on whether you can explain Redux vs Context and apply them in the right scenarios.

Event Handling and Forms in React

Handling user input is one of the most practical interview areas.

1. How do you handle events in React?

<button onClick={() => alert(“Clicked!”)}>Click</button>

Events in React are written in camelCase and passed functions, not strings.

2. What is the difference between controlled and uncontrolled components?

Controlled: Form inputs managed by React state.
Uncontrolled: Form inputs managed by the DOM.

// Controlled

<input value={value} onChange={e => setValue(e.target.value)} />

// Uncontrolled

<input defaultValue="Hello" ref={inputRef} />

3. How do you handle form validation?

Simple validation: Using onChange handlers.
Complex validation: Libraries like Formik or React Hook Form (but explain conceptually).

4. How do you prevent default form submission behavior?

<form onSubmit={e => { e.preventDefault(); alert(“Submitted!”); }}>

  <button type="submit">Submit</button>

</form>

These React coding interview questions test your ability to handle everyday interactions, a must for frontend developers.

React Router and Navigation

Routing is a core part of React apps. Expect at least one question on React Router.

1. How does React Router work?

React Router lets you map URLs to components.

import { BrowserRouter, Routes, Route } from “react-router-dom”;

<BrowserRouter>

  <Routes>

    <Route path="/" element={<Home />} />

    <Route path="/about" element={<About />} />

  </Routes>

</BrowserRouter>

2. Difference between BrowserRouter and HashRouter

BrowserRouter: Uses HTML5 history API (clean URLs).
HashRouter: Uses # in the URL (good for static file hosting).

3. How do you use useParams and useNavigate?

import { useParams, useNavigate } from “react-router-dom”;

function User() {

  const { id } = useParams();

  const navigate = useNavigate();

  return (

    <div>

      <p>User ID: {id}</p>

      <button onClick={() => navigate(“/”)}>Go Home</button>

    </div>

  );

}

4. How do you handle protected routes in React?

function PrivateRoute({ children }) {

  const isAuth = localStorage.getItem(“token”);

  return isAuth ? children : <Navigate to="/login" />;

}

Routing questions are practical. Many React coding interview questions use React Router to test whether you can handle navigation and protected pages.

Performance Optimization in React

Performance optimization is a favorite interview topic because it shows whether you understand how React renders components under the hood. Many React coding interview questions focus on avoiding unnecessary re-renders and improving efficiency.

1. How do you prevent unnecessary re-renders?

React re-renders a component whenever its state or props change. To prevent unnecessary re-renders:

Split large components into smaller ones.
Use React.memo to memoize functional components.
Use useCallback and useMemo to memoize functions and values.
Avoid creating new objects/arrays inside JSX directly.

const Child = React.memo(({ value }) => <p>{value}</p>);

2. What is React.memo and when should you use it?

React.memo is a higher-order component that prevents a child from re-rendering unless its props change.

const Greeting = React.memo(function Greeting({ name }) {

  console.log(“Rendered”);

  return <h1>Hello, {name}</h1>;

});

Answer: Use React.memo when a component receives the same props frequently and doesn’t need to re-render.

3. Difference between useMemo and useCallback

useMemo: Memoizes values.
useCallback: Memoizes functions.

const memoizedValue = React.useMemo(() => expensiveCalc(num), [num]);

const memoizedFn = React.useCallback(() => handleClick(value), [value]);

4. How do you implement code-splitting and lazy loading?

React allows you to split code into smaller chunks and load them when needed.

import React, { Suspense, lazy } from “react”;

const Profile = lazy(() => import(“./Profile”));

function App() {

  return (

    <Suspense fallback={<div>Loading…</div>}>

      <Profile />

    </Suspense>

  );

}

Answer: Code-splitting improves performance by reducing initial bundle size.

5. How does React’s reconciliation algorithm work?

React uses the virtual DOM and a process called diffing:

Compares the new virtual DOM with the old one.
Updates only nodes that changed.
Uses the key prop to optimize list rendering.

Performance-related React coding interview questions test whether you can keep apps smooth and efficient.

Testing React Applications

Testing ensures your components work as expected. Interviewers often ask about testing strategies in React.

1. How do you test a React component with Jest?

import { render, screen } from “@testing-library/react”;

import App from “./App”;

test(“renders hello text”, () => {

  render(<App />);

  expect(screen.getByText(“Hello”)).toBeInTheDocument();

});

Answer: Jest with React Testing Library allows you to render a component and assert its behavior.

2. Difference between shallow rendering and full rendering

Shallow rendering: Renders only one level deep (ignores child components). Good for unit tests.
Full rendering: Renders the entire component tree. Good for integration tests.

3. How does React Testing Library differ from Enzyme?

Enzyme: Lets you test implementation details.
React Testing Library: Encourages testing components as a user would interact with them.

4. How do you test events like button clicks?

import { render, fireEvent } from “@testing-library/react”;

import Counter from “./Counter”;

test(“increments counter”, () => {

  const { getByText } = render(<Counter />);

  fireEvent.click(getByText(“Increment”));

  expect(getByText(“1”)).toBeInTheDocument();

});

Testing-related React coding interview questions check if you know how to validate component behavior, not just implementation.

Advanced React Coding Interview Questions

These advanced React coding interview questions are often asked for senior frontend roles to test deep knowledge of React.

1. What are error boundaries and how do you use them?

Error boundaries catch runtime errors in components.

class ErrorBoundary extends React.Component {

  state = { hasError: false };

  static getDerivedStateFromError() {

    return { hasError: true };

  }

  componentDidCatch(error, info) {

    console.log(error, info);

  }

  render() {

    return this.state.hasError ? <h1>Error occurred</h1> : this.props.children;

  }

}

2. What are portals in React?

Portals let you render children into a DOM node outside the parent hierarchy.

ReactDOM.createPortal(<Modal />, document.getElementById(“modal-root”));

3. What is concurrent rendering in React 18?

Concurrent rendering allows React to interrupt rendering and prioritize urgent updates. Features like automatic batching, useTransition, and startTransition improve performance.

4. How does server-side rendering (SSR) work in React?

React components are rendered on the server into HTML.
HTML is sent to the client, making the page load faster.
React then hydrates the page to make it interactive.

Frameworks like Next.js make SSR easier.

These advanced React coding interview questions separate intermediate developers from senior engineers by testing error handling, rendering, and scalability.

Practice Section: Mock React Coding Interview Questions

Here are some mock interview-style problems with solutions:

1. Build a counter with increment and decrement using useState

function Counter() {

  const [count, setCount] = React.useState(0);

  return (

    <>

      <button onClick={() => setCount(count – 1)}>-</button>

      <span>{count}</span>

      <button onClick={() => setCount(count + 1)}>+</button>

    </>

  );

}

2. Fetch data from an API with useEffect and display it

function Users() {

  const [users, setUsers] = React.useState([]);

  React.useEffect(() => {

    fetch(“/api/users”)

      .then(res => res.json())

      .then(data => setUsers(data));

  }, []);

  return <ul>{users.map(u => <li key={u.id}>{u.name}</li>)}</ul>;

}

3. Build a to-do list with add and remove functionality

function Todo() {

  const [tasks, setTasks] = React.useState([]);

  const [input, setInput] = React.useState(“”);

  return (

    <>

      <input value={input} onChange={e => setInput(e.target.value)} />

      <button onClick={() => setTasks([…tasks, input])}>Add</button>

      <ul>

        {tasks.map((t, i) => (

          <li key={i}>

            {t} <button onClick={() => setTasks(tasks.filter((_, idx) => idx !== i))}>Remove</button>

          </li>

        ))}

      </ul>

    </>

  );

}

4. Implement dark mode toggle using Context API

const ThemeContext = React.createContext();

function App() {

  const [theme, setTheme] = React.useState(“light”);

  return (

    <ThemeContext.Provider value={{ theme, setTheme }}>

      <Toggle />

    </ThemeContext.Provider>

  );

}

function Toggle() {

  const { theme, setTheme } = React.useContext(ThemeContext);

  return (

    <button onClick={() => setTheme(theme === “light” ? “dark” : “light”)}>

      Toggle Theme

    </button>

  );

}

5. Optimize a list rendering component with React.memo

const ListItem = React.memo(({ item }) => <li>{item}</li>);

function List({ items }) {

  return <ul>{items.map((i, idx) => <ListItem key={idx} item={i} />)}</ul>;

}

Practicing full problems like these will prepare you for real React coding interview questions that require hands-on coding.

Tips for Solving React Coding Interview Questions

Here are strategies to perform your best in interviews:

Write clean, modular components: Keep components small and reusable.
Break down problems: Tackle big features by splitting them into smaller parts.
Always explain state vs props: Many interviewers check if you know this difference.
Think about performance early: Use memoization and splitting when necessary.
Talk through your reasoning: Explain not just what you’re coding but why.
Be ready to compare React with Angular or Vue: Employers may ask why React is a better choice in certain cases.

With these habits, you’ll show confidence and clarity when solving React coding interview questions.

Wrapping Up

React is one of the most valuable skills for frontend developers. It involves understanding how React works at scale, optimizing performance, and solving real-world problems.

In this guide, you’ve covered the full range of React coding interview questions, from fundamentals like JSX and props to advanced topics like concurrent rendering and SSR. You’ve also walked through practice problems that simulate the real interview experience.

Mastering React coding interview questions will give you confidence in any frontend interview. Keep practicing, explore more guides and resources, and challenge yourself with new problems every day.

React Coding Interview Questions and Answers (2025)

Why React Is a Popular Choice in Coding Interviews

Categories of React Coding Interview Questions

Basic React Coding Interview Questions

1. What is JSX, and why is it used?

2. Difference between functional and class components

3. What are props in React?

4. How is state different from props?

5. Explain virtual DOM and how React uses it

Component Lifecycle Methods

1. What are the phases of a React component lifecycle?

2. Difference between componentDidMount, componentDidUpdate, and componentWillUnmount

3. How do you fetch data in lifecycle methods?

4. Why were lifecycle methods replaced by hooks?

React Hooks in Coding Interviews

1. What is useState and how does it work?

2. How does useEffect replace lifecycle methods?

3. Explain useContext with an example

4. What are custom hooks and when should you use them?

5. Difference between useMemo and useCallback

State Management: Redux and Context API

1. What problem does Redux solve?

2. Explain actions, reducers, and the store

3. Difference between Redux and Context API

4. When should you use Redux over Context?

5. How does middleware like Redux Thunk work?

Event Handling and Forms in React

1. How do you handle events in React?

2. What is the difference between controlled and uncontrolled components?

3. How do you handle form validation?

4. How do you prevent default form submission behavior?

React Router and Navigation

1. How does React Router work?

2. Difference between BrowserRouter and HashRouter

3. How do you use useParams and useNavigate?

4. How do you handle protected routes in React?

Performance Optimization in React

1. How do you prevent unnecessary re-renders?

2. What is React.memo and when should you use it?

3. Difference between useMemo and useCallback

4. How do you implement code-splitting and lazy loading?

5. How does React’s reconciliation algorithm work?

Testing React Applications

1. How do you test a React component with Jest?

2. Difference between shallow rendering and full rendering

3. How does React Testing Library differ from Enzyme?

4. How do you test events like button clicks?

Advanced React Coding Interview Questions

1. What are error boundaries and how do you use them?

2. What are portals in React?

3. What is concurrent rendering in React 18?

4. How does server-side rendering (SSR) work in React?

Practice Section: Mock React Coding Interview Questions

1. Build a counter with increment and decrement using useState

2. Fetch data from an API with useEffect and display it

3. Build a to-do list with add and remove functionality

4. Implement dark mode toggle using Context API

5. Optimize a list rendering component with React.memo

Tips for Solving React Coding Interview Questions

Wrapping Up

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