factorial of a number

Question

I have the following code but it is not giving perfect result for factorial can u find it out plz

Answer 1

A slight edit to Anton's code:

function fact(x) {
   if(x>0)
       return x* fact(x-1);
   if(x===0)
       return 1;
   return null;

}

(factorial of a negative doesn't exist, but factorial of 0 is equal to 1, in this case, if a number is smaller than 0, the function will return null)