Another update from ingydotnet^djgoku

Task/Factorial/JavaScript/factorial-1.js

@@ -1,7 +1,12 @@
 function factorial(n) {
-    var x = 1;
-    for (var i = 2; i <= n; i++) {
-        x *= i;
-    }
-    return x;
+  //check our edge case
+  if (n < 0) { throw "Number must be non-negative"; }
+
+  var sum = 1;
+  //we skip zero and one since both are 1 and are identity
+  while (n > 1) {
+    sum *= n;
+    n -= 1;
+  }
+  return sum;
 }

Task/Factorial/JavaScript/factorial-2.js

@@ -1,3 +1,11 @@
-function factorial(n) {
-    return n < 2 ? 1 : n * factorial(n - 1);
-}
+(function(x) {
+
+  var memo = {};
+
+  function factorial(n) {
+    return n < 2 ? 1 : memo[n] || (memo[n] = n * factorial(n - 1));
+  }
+
+  return factorial(x);
+
+})(18);

Task/Factorial/JavaScript/factorial-3.js

@@ -1,8 +1 @@
-function range(n) {
-  for (let i = 1; i <= n; i++)
-    yield i;
-}
-
-function factorial(n) {
-  return [i for (i in range(n))].reduce(function(a, b) a*b, 1);
-}
+6402373705728000

Task/Factorial/JavaScript/factorial-4.js

@@ -0,0 +1 @@
+var factorial = n => (n < 2) ? 1 : n * factorial(n - 1);