What are JavaScript closures and how are they used?

Short answer: A closure is created when a function remembers variables from its outer scope, even after that outer function has finished executing. Example: function makeCounter() { let count = 0;

Example code

return function() {
return ++count; }; }
const counter = makeCounter(); console.log(counter()); // 1 console.log(counter()); // 2 ✅ Use cases: data privacy, memoization, and function factories.

Real-world example (ShopNest)

In ShopNest’s cart UI, a click handler closes over productId. Use let in loops so each button keeps the correct id.

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.