Update calculator.js

calculator/calculator.js

@@ -19,6 +19,17 @@ function power(a, b) {
 }
 
 function factorial(n) {
+  if (n == 0) return 1;
+  let product = 1;
+  for (let i = n; i > 0; i--) {
+    product *= i;
+  }
+  return product;
+}
+
+// This is another implementation of Factorial that uses recursion
+// THANKS to @ThirtyThreeB!
+function recursiveFactorial(n) {
   if (n===0){
     return 1;
   }