What is a closure?

Short answer: A closure is a function that retains access to variables from its outer scope even after the outer function has executed. Example: function outer() { let count = 0;

Example code

return function inner() { count++; return count; }; }
const counter = outer(); console.log(counter()); // 1 console.log(counter()); // 2

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.