React Hooks useRef and useMemo 2

Question 1

What is a common use case for useRef that does NOT involve DOM access?

Accepted Answer

Storing the previous value of a prop or state

Answer

Storing a previous value in a ref lets you compare current and previous values without triggering re-renders.

Question 2

What hook is semantically related to useMemo but applies to functions instead of values?

Accepted Answer

useCallback

Answer

useCallback memoizes a function reference so it only changes when its dependencies change, analogous to useMemo for values.

Question 3

Why is over-using useMemo considered an anti-pattern?

Accepted Answer

Memoization itself has overhead; the benefit only justifies complex computations

Answer

Every useMemo call has bookkeeping cost, so memoizing simple or fast operations can be slower than recomputing.

Question 4

How can useRef help avoid stale closures in event handlers?

Accepted Answer

By storing the latest value in ref.current so the handler always reads up-to-date data

Answer

Storing the current value in a ref lets an event handler read the latest value without being recreated on every render.

Question 5

Will useMemo run during server-side rendering (SSR)?

Accepted Answer

Yes, it runs on both server and client

Answer

useMemo runs during SSR just like on the client, though React does not guarantee caching between server requests.

React Practice Test