Simple iterative way to calculate the nth number in the fibonacci sequence

fib.js

var fib = function (n) {
  var i,
      fn = 0,
      f1 = 0,
      f2 = 1;

  if (n < 2) return n;

  for (i = 2; i <= n; i++) {
    fn = f1 + f2;
    f1 = f2;
    f2 = fn;
  }

  return fn;
};

console.log(fib(0)); // 0
console.log(fib(1)); // 1
console.log(fib(2)); // 1
console.log(fib(3)); // 2
console.log(fib(4)); // 3
console.log(fib(5)); // 5
console.log(fib(6)); // 8
console.log(fib(7)); // 13
console.log(fib(8)); // 21