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Prepare for your next frontend developer interview with this comprehensive list of React interview questions and detailed answers. Covers basics, intermediate topics like hooks, and advanced topics including Redux, Context API, performance tuning, and more. Perfect for junior to senior React developers in 2025.

👶 Basic React Interview Questions

❓ What is React?

Answer:

React is a JavaScript library developed by Facebook for building fast and interactive user interfaces. It enables component-based architecture, making UIs modular and reusable.

❓ What are the main features of React?

Answer:

• JSX: HTML-like syntax in JavaScript
• Components: Reusable UI building blocks
• Virtual DOM: Optimized updates to the real DOM
• Unidirectional Data Flow: Predictable and maintainable data flow

❓ What is JSX?

Answer:

JSX (JavaScript XML) allows writing HTML-like code in JavaScript. It improves readability and makes it easier to write React components.

❓ What are components in React?

Answer:

Components are independent, reusable pieces of UI.

They can be:

• Functional Components: Use hooks and are stateless or stateful
• Class Components: Use this.state and lifecycle methods (less common now)

❓ What is the difference between state and props?

StatePropsMutabilityMutableImmutableScopeLocal to componentPassed from parentUseTrack changes inside componentPass data to child components

⚙️ Intermediate React Interview Questions

❓ What is the Virtual DOM?

Answer:

The Virtual DOM is an in-memory representation of the real DOM. When state changes, React compares the new Virtual DOM with the previous one (diffing), and applies only the changes to the actual DOM (reconciliation).

❓ What are Hooks in React?

Answer:

Hooks let you use state and lifecycle features in function components.

Popular hooks:

• useState
• useEffect
• useContext
• useReducer
• useRef

❓ What is useState?

javascript

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

It returns the current state and a function to update it.

❓ What is useEffect?

javascript

useEffect(() => {
  document.title = `You clicked ${count} times`;
}, [count]);

It handles side effects like API calls, subscriptions, and DOM updates.

❓ How do you handle forms in React?

javascript

const [name, setName] = useState("");

const handleChange = (e) => setName(e.target.value);

return (
  <form>
    <label>
      Name: <input type="text" value={name} onChange={handleChange} />
    </label>
  </form>
);

React uses controlled components to manage form data via state.

🚀 Advanced React Interview Questions

❓ What is the Context API?

Answer:

The Context API provides a way to share values (like auth, themes) across components without passing props manually.

javascript

const MyContext = React.createContext();

<MyContext.Provider value="Hello">
  <MyComponent />
</MyContext.Provider>

const MyComponent = () => {
  const value = useContext(MyContext);
  return <div>{value}</div>;
};

❓ What are Higher-Order Components (HOCs)?

Answer:

A higher-order component is a function that takes a component and returns a new one with additional logic.

javascript

function withLoading(Component) {
  return function ({ isLoading, ...props }) {
    return isLoading ? <p>Loading...</p> : <Component {...props} />;
  };
}

❓ What is Redux?

Answer:

Redux is a state management library used with React for managing complex application states using a single store, actions, and reducers.

❓ Difference between useEffect and useLayoutEffect?

useEffectuseLayoutEffectTimingAfter paint (async)Before paint (sync)Use CaseAPI calls, subscriptionsMeasuring layout, DOM mutationsPerformanceNon-blockingBlocking render

❓ How do you optimize React performance?

• Use React.memo to prevent unnecessary re-renders
• Use useCallback and useMemo to memoize functions and values
• Lazy load components with React.lazy and Suspense
• Avoid anonymous functions in render
• Flatten state where possible
• Keep component trees shallow

📌 Summary: Topics to Review for React Interviews

• JSX and Components
• Props vs State
• Functional components and hooks
• useState, useEffect, useRef, useMemo
• Context API
• Redux basics
• HOC pattern
• Performance tuning
• Lifecycle methods vs hooks
• Event handling and controlled forms