¿Qué es un Closure? (versión entrevista)

What is a closure in JavaScript? Provide a real-world use case.

A closure is a function that retains access to the variables of its outer (enclosing) scope even after that scope has finished executing. ```js function makeMultiplier(factor) { // factor lives in makeMultiplier's scope return function(n) { return n * factor; // inner fn closes over 'factor' }; } const triple = makeMultiplier(3); const double = makeMultiplier(2); triple(5); // 15 — 'factor' is 3, remembered double(5); // 10 — independent closure ``` Real-world uses: private state in modules, curried functions, event handler factories, memoization caches, React hooks (useState closes over component state).