Understanding Closures
A closure is the combination of a function bundled together (enclosed) with references to its surrounding state (the lexical environment). In other words, a closure gives you access to an outer function's scope from an inner function.
Why does it matter?
In React development, closures are everywhere—from hooks like useEffect to event handlers. Understanding how they capture variables is key to avoiding stale closure bugs.
function makeCounter() {
let count = 0;
return function() {
return count++;
};
}
const counter = makeCounter();
console.log(counter()); // 0
console.log(counter()); // 1
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