Quiz for useEffect

Q1: What is the main purpose of the useEffect hook?

A. To manage side effects in functional components B. To create new components C. To manage state D. To handle routing

Q2: When does the useEffect hook run by default?

A. Only on initial render B. On every render C. Only on unmount D. Only on state change

Q3: How can you run useEffect only once when the component mounts?

A. By passing an empty dependency array [] B. By not passing any dependencies C. By passing null D. By using setTimeout

Q4: What is the purpose of the cleanup function in useEffect?

A. To execute code before component unmounts or before next effect B. To render JSX C. To fetch data D. To manage state

Q5: How do you specify dependencies for useEffect?

A. As function parameters B. In the dependency array passed as second argument C. In the return statement D. In the component props

Q6: What happens if you omit the dependency array in useEffect?

A. Effect runs only once B. Effect runs on every render C. Effect never runs D. Effect throws an error

Q7: Can useEffect run cleanup code?

A. No B. Yes, by returning a function C. Only with useState D. Only with class components

Q8: Which of these is a common side effect handled by useEffect?

A. Changing CSS B. Fetching API data C. Navigating pages D. Setting component title

Q9: When is the cleanup function inside useEffect called?

A. Before the effect runs again and on unmount B. Only on mount C. Only after render D. Only in development mode

Q10: What can happen if you forget to add dependencies to the dependency array?

A. Effect will never run B. Effect may use stale values or cause bugs C. Component will crash D. Component will freeze

Q11: Can you have multiple useEffect hooks in one component?

A. No B. Yes C. Only two D. Only one per hook type

Q12: How do you prevent useEffect from running on initial render?

A. Use a ref to track initial render B. Pass null as dependencies C. Use useState D. Use class component

Q13: What is the dependency array in useEffect?

A. Array of functions B. Array of state and props to watch C. Array of components D. Array of events

Q14: Which hook would you use to perform data fetching?

A. useState B. useEffect C. useRef D. useContext

Q15: What can you NOT do inside the main function passed to useEffect?

A. Declare variables B. Make API calls C. Return a promise D. Call setState

Q16: How can you run useEffect whenever a specific prop changes?

A. By passing that prop in the dependency array B. By calling setState C. By using useMemo D. By passing it as a function parameter

Q17: Which statement is true about useEffect?

A. It replaces componentDidMount, componentDidUpdate, and componentWillUnmount B. It only replaces componentDidMount C. It only replaces componentWillUnmount D. It replaces render

Q18: Can you perform cleanup asynchronously in useEffect?

A. No B. Yes, using async functions inside cleanup C. Only with promises D. Cleanup must be synchronous

Q19: What is the difference between useEffect and useLayoutEffect?

A. useEffect runs after paint, useLayoutEffect runs before paint B. useEffect is synchronous, useLayoutEffect is asynchronous C. No difference D. useLayoutEffect is deprecated

Q20: Why is it important to specify all dependencies in the useEffect dependency array?

A. To avoid infinite loops and bugs B. To improve styling C. To reduce code size D. To optimize images