Ackermann Function.js

/*
Description:
The Ackermann function is a famous function that played a big role in computability theory as the first exemple of a total computable function that is not primitive recursive.

Since then the function has been a bit simplified but is still of good use. Due to its definition in terms of extremely deep recursion it can be used as a benchmark of a compiler's ability to optimize recursion.

The goal of this kata is to code a function wich will be given two input, m and n, and will return the Ackermann number A(m,n) defined by:

A(m,n) = n+1                          if m=0  
A(m,n) = A(m-1,1)                     if m>0 , n=0
A(m,n) = A(m-1,A(m,n-1))              if m,n > 0
m,n should be non-negative integers, the function should return null (Javascript), None (Python), or nil (Ruby) for other type, non-integer and negative numbers. In C, input is restricted to integer type.
*/
Ackermann=function(m,n) {
    if (m<0||n<0){
        return null
    }
    if (m == 0) {
        return n + 1;
    }
    if (m>0&&n == 0) {
        return Ackermann(m - 1, 1)
    }
    if (m>0&&n>0){
        return Ackermann(m-1,Ackermann(m,n-1))
    }
}