Interview Q&A / React

1. What is the difference between useMemo and useCallback, and when should you not use them?

   useMemo caches the result of a calculation, and useCallback caches a function itself, both until their dependencies change. Use them for expensive calculations or to keep values stable for memoized children or effect dependencies; skip them for cheap work, where they only add complexity.

   IntermediateIn-depth3 min read
2. Why does useCallback often do nothing unless the child is wrapped in React.memo?

   useCallback keeps a function reference stable, but a child still re-renders whenever its parent does unless the child is wrapped in React.memo or the function is a hook dependency. The stable reference only helps where something compares it.

   IntermediateQuick answer1 min read