To calculate factorial

Factorial.js

function factorialize(num) {
  product=1;
  var fast =[];
  if(num>0){
  var ghr= num;
  for(i=1;i<=ghr;i++){
    fast.push(i);
  }
  for(i=0;i<fast.length;i++){
    product=product*fast[i];
    num = product;
 }
  return num;
  }
  else if(num===0) {
    return 1;
    }
  else {
    return "Factorial not possible";
  }
}

factorialize(20);//Here goes your no. of which you want to find factorial