Closures and Lexical Scope

A closure is a function that retains access to its outer scope, even after the outer function has finished executing.

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

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

This works because of lexical scoping — functions remember the environment in which they were created.