quick sort in javascript

                                    const quickSort = array =>
  (function qsort(arr, start, end) {
    if (start >= end) return arr;
    let swapPos = start;

    for (let i = start; i <= end; i++) {
      if (arr[i] <= arr[end]) {
        [arr[swapPos], arr[i]] = [arr[i], arr[swapPos]];
        swapPos++;
      }
    }
    qsort(arr, start, --swapPos - 1);
    qsort(arr, swapPos + 1, end);

    return arr;
  })(Array.from(array), 0, array.length - 1);

                                    var items = [5,3,7,6,2,9];
function swap(items, leftIndex, rightIndex){
    var temp = items[leftIndex];
    items[leftIndex] = items[rightIndex];
    items[rightIndex] = temp;
}
function partition(items, left, right) {
    var pivot   = items[Math.floor((right + left) / 2)], //middle element
        i       = left, //left pointer
        j       = right; //right pointer
    while (i <= j) {
        while (items[i] < pivot) {
            i++;
        }
        while (items[j] > pivot) {
            j--;
        }
        if (i <= j) {
            swap(items, i, j); //sawpping two elements
            i++;
            j--;
        }
    }
    return i;
}

function quickSort(items, left, right) {
    var index;
    if (items.length > 1) {
        index = partition(items, left, right); //index returned from partition
        if (left < index - 1) { //more elements on the left side of the pivot
            quickSort(items, left, index - 1);
        }
        if (index < right) { //more elements on the right side of the pivot
            quickSort(items, index, right);
        }
    }
    return items;
}
// first call to quick sort
var sortedArray = quickSort(items, 0, items.length - 1);
console.log(sortedArray); //prints [2,3,5,6,7,9]

                                    var items = [5, 3, 7, 6, 2, 9];

function swap(items, leftIndex, rightIndex) {
  var temp = items[leftIndex];
  items[leftIndex] = items[rightIndex];
  items[rightIndex] = temp;
}

function partition(items, left, right) {
  var pivot = items[Math.floor((right + left) / 2)], //middle element
    i = left, //left pointer
    j = right; //right pointer
  while (i <= j) {
    while (items[i] < pivot) {
      i++;
    }
    while (items[j] > pivot) {
      j--;
    }
    if (i <= j) {
      swap(items, i, j); //sawpping two elements
      i++;
      j--;
    }
  }
  return i;
}

function quickSort(items, left, right) {
  var index;
  if (items.length > 1) {
    index = partition(items, left, right); //index returned from partition
    if (left < index - 1) {
      //more elements on the left side of the pivot
      quickSort(items, left, index - 1);
    }
    if (index < right) {
      //more elements on the right side of the pivot
      quickSort(items, index, right);
    }
  }
  return items;
}

// first call to quick sort
var sortedArray = quickSort(items, 0, items.length - 1);
console.log(sortedArray); //prints [2,3,5,6,7,9]

                                    const quicksort = arr =>
  arr.length <= 1
    ? arr
    : [
        ...quicksort(arr.slice(1).filter((el) => el < arr[0])),
        arr[0],
        ...quicksort(arr.slice(1).filter((el) => el >= arr[0])),
      ];