// Simplify version

// Itterative
function max1(list){
  var result = -Infinity;
  for (var i = 0; i < list.length; i++) {
    result <= list[i] && (result = list[i]);
  }
  return result;
}

document.write(max1([-1,-2,-3,1,2,3]))

// Recursive
function max(list, max_value) {
  max_value = max_value || -Infinity;
  if (list.length != 0) {
    return max(list.slice(1), (list[0] > max_value ? list[0] : max_value));
  } else {
    return max_value;
  }
}

document.write(max([-1,-2,-3,1,2,3]))