modify javascript quick-sort to copy input

otherwise, input parameter is changed.

Author: adamloving

solutions/javascript/quick-sort.js

@@ -1,11 +1,13 @@
-module.exports = function quickSort (array, compare) {
+'use strict';
+
+module.exports = function quickSort(input, compare) {
   var lesser  = [],
       greater = [],
       pivot;
 
   // Not an array, empty or array of 1 is already sorted
-  if (!Array.isArray(array) || array.length < 2) {
-    return array;
+  if (!Array.isArray(input) || input.length < 2) {
+    return input;
   }
 
   // Create a compare func if not passed in
@@ -15,6 +17,8 @@ module.exports = function quickSort (array, compare) {
     };
   }
 
+  var array = input.slice(0); // make a copy of the array
+
   // Get our pivot, this can be random
   pivot = array.splice(~~(Math.random() * array.length), 1);