Non recursive way to write vibonachy sequence

It is very common interview question i see in many places: write a function which receives a serial number as a parameter and returns a fibonacci number.

// num -> 1 => 0

// num -> 2 => 1

// num -> 3 => 1

// num -> 4 => 2

// num -> 5 => 3

Usually i was quickly writing an answer using a recursion:

function f(num) {
  if (num === 0) return 0;
  if (num === 1 || num === 2 || num === 3) return 1;
  return f(num - 1) + f(num - 2);
}
console.log(f(5))

But ,since i found out that recursion has much more space complexity than iterative way, Here is that i come with trying to implement the fibonacci challenge using iterations (of while loop):

function f(num) { 
  if (num === 1)  return 0;
  if (num === 2 || num === 3) return 1;
  let counter = 4; // important to begin from 4, because we already taked care of 1 and 2 and 3 
  let result = 1, old = 1;
  while (counter <= num) {
    let temp = result;
    result = old + result;
    counter++;
    old = temp;    
  }
  return result;
}
let num = 1;
console.log(`${num} => ${f(num)}`)