What is the difference between useEffect and useLayoutEffect?

Short answer: Feature useEffect useLayoutEffect When it runs After paint Before paint (after DOM mutation) Use for Async tasks, data fetching Measuring DOM, sync layout Blocking paint? ❌ No ✅ Yes (can cause jank) 🔍 Use useLayoutEffect only when layout measurement or synchronously modifying DOM is necessary.

Real-world example (ShopNest)

ShopNest’s cart icon uses useState for count and useEffect to load the cart once on mount.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.