Zoddy

var fibonacci = function(n, _a, _b) {
  _a = _a || -1;
  _b = _b || 1;

  return (n === 0 || n === 2) ? [_a, _b] : fibonacci(
    n - 1 + 2 * (n < 0),
    _b - _a * (n < 0),
    _a + _b * (n > 0)
  );
};