why ? 24

Question

What is the output of this code?
function p(m) {
if (m==1)
{
return m;
}
else
{
return m * p(m-1);
}
} alert(p(4)); answer 24

Answer 1

Replace m with 4:

function p(m) { //m=4
if (m==1) { // 4==1 is false
return m;
} else { //else block is executed
return m * p(m-1); //4 * p(3)
}
}

Now replace m with 3 so you should get p(3) = 3 * p(2)
And p(2) = 2 * p(1) .

Now in p(1) m==1 is true and it returns 1 so p(1) = 1

Putting it together you get
p(4) = 4 * p(3) = 4 * 3 * p(2) =
4*3*2*p(1)= 4*3*2*1= 24

Answer 2

Its a recursive function for calculate factorial of a number... It call recursively itself multply param m with factorial of m-1 while m==1 then:
p(4) = 4 * p(3)
p(3)= 3 * p(2)
p(2)= 2 * p(1)
p(1)= 1

thats:
4*3*2*1= 24