Closure

In computer programming, a closure is a technique for implementing lexically scoped name binding in a language with first-class functions.

In JavaScript, a function creates a closure context. As shown by the following code, the inner function maintains access to the count variable even after createCounter() has finished executing.

function createCounter() {
  let count = 0;
  return function () {
    count += 1;
    return count;
  };
}

const counter = createCounter();
console.log(counter()); // 1
console.log(counter()); // 2
console.log(counter()); // 3