quick_sort.js

const items = [5, 3, 7, 6, 2, 9];
const swap = (items, leftIndex, rightIndex) => {
  const temp = items[leftIndex];
  items[leftIndex] = items[rightIndex];
  items[rightIndex] = temp;
};
const partition = (items, left, right) => {
  const pivot = items[Math.floor((right + left) / 2)]; //middle element
  let i = left; //left pointer
  let 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;
};

const quickSort = (items, left, right) => {
  let 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]