1. What is the closure?

Function A, declared inside another function B. Function A has access to variables of function B even if function B finished execution already

function createCounter() {
  let count = 0;
  function increment() {
    count++;
    console.log(count);
  }
  return increment;
}
const counter = createCounter(); // createCounter finished execution
counter(); // 1  increment still has access to variable count and it modifies it
counter(); // 2
counter(); // 3