Update 02_recursive_sum.js (#168)

First, congratulations for the work, the book is very instructive.

In this case, as described in the book, if the list is empty it returns zero, otherwise we apply recursion.

Co-authored-by: Aditya Bhargava <bluemangroupie@gmail.com>

04_quicksort/javascript/02_recursive_sum.js

@@ -5,9 +5,9 @@
  * @param {Array} array Array of numbers
  * @returns {number} Sum of the numbers
  */
-function sumRecursive(array) {
-  if (array.length == 1) return array[0];
-  return array[0] + sumRecursive(array.slice(1));
+function sumRecursive(arr) {
+  if (arr.length == 0) return 0;
+  return arr[0] + sumRecursive(arr.slice(1));
 }
 
 console.log(sumRecursive([1, 2, 3, 4])); // 10