javascript - Why does my factorial function always return one? -

i trying write piece of code solve coderbyte challenge, calculate number's factorial. every time run it, factorial generated one. doing wrong?

var num var array1 = new array();  function firstfactorial(num) {          (var = num; i>0; i--){        // 8 , 7, 6 , 5         (var y = 0; y<num ; y++){   // 0, 1, 2, 3, 4         array1[y]=i;       // have array looks [8,7,6,5,4,3,2,1]         };     };     var sum = 1     (var x = 0; x<array1.length; x++){  // want run array, reading #s         sum = sum * array1[x];         return sum;     };     return sum }; 

a few issues.

1/ minor but, when multiply 2 numbers, product, not sum.

2/ returned value within loop mean, if fixed other problems, return prematurely without having multiplied numbers.

3/ nested loop not fill array way describe, should check after population. think loops expressed pseudo-code:

for = num downto 1 inclusive:     y = 0 num-1 inclusive:         array1[y] = 

you can see inner loop populating entire array value of current i. last iteration of outer loop, i one, sets entire array ones.

4/ in case, don't need array store numbers 1 n, use numbers 1 n directly. (again, pseudo-code):

def fact(n):     prod = 1     = 2 n inclusive:         prod = prod *     return prod