Javascript/Math: editing file name

Maths/Factorial.js

@@ -0,0 +1,53 @@
+/*
+    author: PatOnTheBack
+    license: GPL-3.0 or later
+
+    Modified from:
+        https://github.com/TheAlgorithms/Python/blob/master/maths/factorial_python.py
+
+    This script will find the factorial of a number provided by the user.
+
+    More about factorials:
+        https://en.wikipedia.org/wiki/factorial
+*/
+
+'use strict'
+
+function calcRange (num) {
+  // Generate a range of numbers from 1 to `num`.
+  var i = 1
+  var range = []
+  while (i <= num) {
+    range.push(i)
+    i += 1
+  }
+  return range
+}
+
+function calcFactorial (num) {
+  var factorial
+  var range = calcRange(num)
+
+  // Check if the number is negative, positive, null, undefined, or zero
+  if (num < 0) {
+    return 'Sorry, factorial does not exist for negative numbers.'
+  }
+  if (num === null || num === undefined) {
+    return 'Sorry, factorial does not exist for null or undefined numbers.'
+  }
+  if (num === 0) {
+    return 'The factorial of 0 is 1.'
+  }
+  if (num > 0) {
+    factorial = 1
+    range.forEach(function (i) {
+      factorial = factorial * i
+    })
+    return 'The factorial of ' + num + ' is ' + factorial
+  }
+}
+
+// Run `factorial` Function to find average of a list of numbers.
+
+var num = console.log('Enter a number: ')
+console.log(calcFactorial(num))