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Entry Level React Interview Questions

10 questions and relatively short but comprehensive answers for entry level devs.

Feb 1, 202310 min read
Entry Level React Interview Questions

Introduction

Preparing for your first React developer role? Here are 10 essential interview questions with concise explanations to help you ace your interview.

What is React?

React is a JavaScript library for building user interfaces. It was developed by Facebook and is maintained by Meta and a community of developers.

Why React?

  • Component-based architecture
  • Reusable UI components
  • Virtual DOM for better performance
  • Large ecosystem and community support
  • One-way data binding

10 Interview Questions

1. What is JSX?

JSX is a syntax extension for JavaScript that looks similar to HTML. It allows us to describe UI directly inside JavaScript in a readable way.

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

2. What are props?

Props are read-only inputs passed from a parent component to a child component. They let components stay reusable and configurable.

function Welcome(props) {
  return <h1>Hello, {props.name}</h1>;
}

3. What is state?

State is built-in React data that belongs to a component. When state changes, React re-renders the component with the updated value.

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

4. What is a component?

A component is a reusable building block of a React app. Components can return JSX and manage logic, state, and props.

function Button() {
  return <button>Click me</button>;
}

5. What is the virtual DOM?

The virtual DOM is a lightweight in-memory representation of the real DOM. React compares updates there first and changes only what is necessary in the browser.

// React updates the virtual DOM first
setItems((current) => [...current, newItem]);

6. What is useState?

useState is a React Hook that lets function components store and update local state.

const [isOpen, setIsOpen] = useState(false);
setIsOpen(true);

7. What is useEffect?

useEffect is a Hook used for side effects like fetching data, subscribing to events, or syncing values after render.

useEffect(() => {
  document.title = `Count: ${count}`;
}, [count]);

8. What is key in lists?

A key helps React identify which list items changed, were added, or were removed. Stable keys improve rendering correctness and performance.

items.map((item) => <li key={item.id}>{item.name}</li>);

9. What is conditional rendering?

Conditional rendering means showing different UI based on state or props using normal JavaScript conditions.

{isLoggedIn ? <Dashboard /> : <SignInPrompt />}

10. What is React Router?

React Router is a routing library for React applications. It helps map URLs to components for navigation in single-page apps.

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

Tips & Resources

For interview prep, focus on explaining concepts in your own words instead of memorizing one-line definitions. Small working examples often help you stand out more than long theory answers.

  • Practice answering out loud
  • Build one small demo per concept
  • Review hooks, props, state, and rendering flow

Conclusion

A strong beginner React interview usually comes down to clarity. If you understand the basics well and can explain them simply, you are already in a strong position.

Want to practice more?

Check out more articles on React, JavaScript, TypeScript, and frontend engineering.

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