1function quicksort(array) {
2  if (array.length <= 1) {
3    return array;
4  }
5
6  var pivot = array[0];
7  
8  var left = []; 
9  var right = [];
10
11  for (var i = 1; i < array.length; i++) {
12    array[i] < pivot ? left.push(array[i]) : right.push(array[i]);
13  }
14
15  return quicksort(left).concat(pivot, quicksort(right));
16};

1const quicksort = arr =>
2  arr.length <= 1
3    ? arr
4    : [
5        ...quicksort(arr.slice(1).filter((el) => el < arr[0])),
6        arr[0],
7        ...quicksort(arr.slice(1).filter((el) => el >= arr[0])),
8      ];

1const quickSort = array =>
2  (function qsort(arr, start, end) {
3    if (start >= end) return arr;
4    let swapPos = start;
5
6    for (let i = start; i <= end; i++) {
7      if (arr[i] <= arr[end]) {
8        [arr[swapPos], arr[i]] = [arr[i], arr[swapPos]];
9        swapPos++;
10      }
11    }
12    qsort(arr, start, --swapPos - 1);
13    qsort(arr, swapPos + 1, end);
14
15    return arr;
16  })(Array.from(array), 0, array.length - 1);

1var items = [5, 3, 7, 6, 2, 9];
2
3function swap(items, leftIndex, rightIndex) {
4  var temp = items[leftIndex];
5  items[leftIndex] = items[rightIndex];
6  items[rightIndex] = temp;
7}
8
9function partition(items, left, right) {
10  var pivot = items[Math.floor((right + left) / 2)], //middle element
11    i = left, //left pointer
12    j = right; //right pointer
13  while (i <= j) {
14    while (items[i] < pivot) {
15      i++;
16    }
17    while (items[j] > pivot) {
18      j--;
19    }
20    if (i <= j) {
21      swap(items, i, j); //sawpping two elements
22      i++;
23      j--;
24    }
25  }
26  return i;
27}
28
29function quickSort(items, left, right) {
30  var index;
31  if (items.length > 1) {
32    index = partition(items, left, right); //index returned from partition
33    if (left < index - 1) {
34      //more elements on the left side of the pivot
35      quickSort(items, left, index - 1);
36    }
37    if (index < right) {
38      //more elements on the right side of the pivot
39      quickSort(items, index, right);
40    }
41  }
42  return items;
43}
44
45// first call to quick sort
46var sortedArray = quickSort(items, 0, items.length - 1);
47console.log(sortedArray); //prints [2,3,5,6,7,9]

1var items = [5,3,7,6,2,9];
2function swap(items, leftIndex, rightIndex){
3    var temp = items[leftIndex];
4    items[leftIndex] = items[rightIndex];
5    items[rightIndex] = temp;
6}
7function partition(items, left, right) {
8    var pivot   = items[Math.floor((right + left) / 2)], //middle element
9        i       = left, //left pointer
10        j       = right; //right pointer
11    while (i <= j) {
12        while (items[i] < pivot) {
13            i++;
14        }
15        while (items[j] > pivot) {
16            j--;
17        }
18        if (i <= j) {
19            swap(items, i, j); //sawpping two elements
20            i++;
21            j--;
22        }
23    }
24    return i;
25}
26
27function quickSort(items, left, right) {
28    var index;
29    if (items.length > 1) {
30        index = partition(items, left, right); //index returned from partition
31        if (left < index - 1) { //more elements on the left side of the pivot
32            quickSort(items, left, index - 1);
33        }
34        if (index < right) { //more elements on the right side of the pivot
35            quickSort(items, index, right);
36        }
37    }
38    return items;
39}
40// first call to quick sort
41var sortedArray = quickSort(items, 0, items.length - 1);
42console.log(sortedArray); //prints [2,3,5,6,7,9]
43