10 interview questions regarding ReactJS useEffect() Hook

10 interview questions regarding ReactJS useEffect() Hook

Here are 10 interview questions regarding the useEffect hook in React:

  1. What is the purpose of the useEffect hook in React?

    • Describe when and why it's used in a React component.
  2. How does useEffect differ from componentDidMount and componentDidUpdate in class components?

    • Explain the lifecycle equivalencies of useEffect in functional components.
  3. What is the dependency array in the useEffect hook, and why is it important?

    • Discuss how dependencies influence the behavior of the useEffect hook.
  4. What happens if you omit the dependency array in the useEffect hook?

    • Explain the potential issues and why it's considered a best practice to include dependencies.
  5. How can you replicate the behavior of componentWillUnmount with useEffect?

    • Discuss cleanup functions and their role in preventing memory leaks.
  6. Explain the concept of multiple useEffect hooks in a single component.

    • Discuss scenarios where multiple useEffect hooks might be useful and how they behave.
  7. How do you run an effect only once when the component mounts?

    • Describe the pattern for achieving an effect that runs only on mount using useEffect.
  8. What are the common use cases for the useEffect hook?

    • Discuss scenarios where using useEffect is beneficial for managing side effects in a React component.
  9. How can you cancel or clean up an effect in useEffect?

    • Explain the cleanup function and its role in preventing memory leaks or undesired side effects.
  10. Discuss potential pitfalls or common mistakes related to the useEffect hook.

    • Talk about issues like infinite loops, missing dependency warnings, or incorrect dependency usage.


These questions cover various aspects of the useEffect hook in React, including its purpose, dependency management, lifecycle equivalence, cleanup functions, and common usage patterns.

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