Factorial recursive to iterative

fact.js

let fact0 = (n) => {
  if (n > 0) {
    return n * fact0(n - 1);
  } else
    return 1;
}

console.log(fact0(5, (x) => x))

let fact1 = (n, k) => {
  if (n > 0) {
    return fact1(n - 1, (x) => k(n * x))
  } else {
    return k(1)
  }
}

console.log(fact1(5, (x) => x))

// type cont = {n:int , k:cont} | null

let fact2 = (n, k) => {
  let res = 1;
  while (true) {
    if (n > 0) {
      k = { n: n, next: k }; // new cont (stack push)
      n = n - 1;
    } else {
      if (k != null) {
        res = res * k.n;
        k = k.next; // (stack pop) 
      }
      else
        return res;
    }
  }
}

console.log(fact2(5, null));