I am writing an algorithm to determine the greatest common divisor of two integers.

```
function gcd(a,b) {
if (b == 0) {
return a;
}
else {
return gcd(b, a%b);
}
}
gcd(1,5);
```

This function starts to work. b does equal 0 after the second iteration. At that point, a is equal to 1, and that is the answer we expected. The problem is that it iterates once more and b becomes undefined. a also becomes undefined. When I console.log(a) in the if b==0 conditional, I get two values for a. The first is 1, the second is undefined. If b == 0, we should return a and the function should end. Why am I getting undefined here?