Can you explain what a closure is in JavaScript and how it works?

A closure in JavaScript is a function that 'remembers' the environment in which it was created, even if that environment is no longer active. In simpler terms, a function inside another function can access the variables of the outer function after the outer function has finished executing.

This works because when a function is created, a reference to the lexical environment where it was declared is stored.

Example:

function outer() {
  let count = 0;
  return function inner() {
    count++;
    console.log(count);
  };
}

const counter = outer();
counter(); // 1
counter(); // 2

Here, inner closes over the variable count from outer, preserving its state between calls.