JS Closures

closures.js

function makeCounter(i) {
  let count = i;
  let toString = () => `The count is ${count}.`;
  return {
    add: () => ++count,
    sub: () => --count,
    val: () => count,
    toString: toString
  };
}

var counter = makeCounter(0);
console.log(counter.add()) // 1 
console.log(counter.val()) // 1
console.log(counter.sub()) // 0
console.log(counter.add()) // 1
console.log(counter.add()) // 2
console.log(counter.toString()) // The count is 2.