This efficient JavaScript function returns the greatest common divisor of a series of numbers.

1. function GCD(nums)
2. {
3.  if(!nums.length)
4.  return 0;
5.  for(var r, a, i = nums.length – 1, GCDNum = nums[i]; i;)
6.  for(a = nums[–i]; r = a % GCDNum; a = GCDNum, GCDNum = r);
7.  return GCDNum;
8. }
10. alert(GCD([12, 8, 4])); // Will return 4