Increase readability, update code style and optimise for modern JavaScript (#273)

* Remove loops on recursive example, increase readability and optimise

* Update style and optimise

* Update 01_loop_sum_reduce_version.js

Update style

* Update style

* Rename identificators

* Rename identificators

* Convert shift to splice

04_quicksort/javascript/01_loop_sum_reduce_version.js

@@ -5,10 +5,6 @@
  * @param {Array} array Array of numbers
  * @returns {number} Sum of the numbers
  */
-function sumReduce(array) {
-  return array.reduce(function(prev, cur) {
-    return prev + cur;
-  });
-}
+const sumReduce = (array) => array.reduce((prev, cur) => prev + cur, 0);
 
 console.log(sumReduce([1, 2, 3, 4])); // 10

04_quicksort/javascript/02_recursive_sum.js

@@ -1,13 +1,14 @@
-"use strict";
+'use strict';
 
 /**
  * Sums values in the array by recursive
  * @param {Array} array Array of numbers
  * @returns {number} Sum of the numbers
  */
-function sumRecursive(arr) {
-  if (arr.length == 0) return 0;
+const sumRecursive = (arr = []) => {
+  if (!arr.length) return 0;
   return arr[0] + sumRecursive(arr.slice(1));
-}
+};
+
 
 console.log(sumRecursive([1, 2, 3, 4])); // 10