Added Quick Sort in JavaScript

Sorting/QuickSort.js

@@ -0,0 +1,55 @@
+const quickSort = (arr, start, end) => {
+
+  if(start < end) {
+
+    // You can learn about how the pivot value is derived in the comments below
+    let pivot = partition(arr, start, end)
+
+    // Make sure to read the below comments to understand why pivot - 1 and pivot + 1 are used
+    // These are the recursive calls to quickSort
+    quickSort(arr, start, pivot - 1)
+    quickSort(arr, pivot + 1, end)
+  } 
+
+}
+
+const partition = (arr, start, end) => { 
+  let pivot = end
+  // Set i to start - 1 so that it can access the first index in the event that the value at arr[0] is greater than arr[pivot]
+  // Succeeding comments will expound upon the above comment
+  let i = start - 1
+  let j = start
+
+  // Increment j up to the index preceding the pivot
+  while (j < pivot) {
+
+    // If the value is greater than the pivot increment j
+    if (arr[j] > arr[pivot]) {
+      j++
+    }
+
+    // When the value at arr[j] is less than the pivot:
+    // increment i (arr[i] will be a value greater than arr[pivot]) and swap the value at arr[i] and arr[j]
+    else {
+      i++
+      swap(arr, j, i)
+      j++
+    }
+
+  }
+
+  //The value at arr[i + 1] will be greater than the value of arr[pivot]
+  swap(arr, i + 1, pivot)
+
+  //You return i + 1, as the values to the left of it are less than arr[i+1], and values to the right are greater than arr[i + 1]
+  // As such, when the recursive quicksorts are called, the new sub arrays will not include this the previously used pivot value
+  return i + 1
+}
+
+const swap = (arr, firstIndex, secondIndex) => {
+  let temp = arr[firstIndex]
+  arr[firstIndex] = arr[secondIndex]
+  arr[secondIndex] = temp
+}
+
+quickSort(arr, 0, arr.length - 1)