JavaScript

Explaining closures in one sentence

"A function that remembers the scope it was created in." Three examples of when closures help — and when they bite.

By: Your Name
Published: October 2, 2026
Reading: 2 min read

A closure is a function that remembers the lexical scope it was declared in.

Building a counter

function createCounter() {
  let count = 0;
  return {
    increment: () => ++count,
    current: () => count,
  };
}

const counter = createCounter();
counter.increment();
counter.increment();
console.log(counter.current()); // 2

Nothing outside can touch count, yet the returned functions keep a live reference to it.

The classic trap: loops and `var`

for (var i = 0; i < 3; i++) {
  setTimeout(() => console.log(i)); // 3, 3, 3
}

Switch to let and each iteration gets a fresh binding, so you'll see 0, 1, 2.

Takeaways

Reach for closures when you want private state.
Long-lived closures keep their captured values in memory — be deliberate.

JavaScript