Quick sort basically picks a pivot element in the given array, sorts it by moving larger items to the right and the smaller elements to the left of the pivot element

quickSort.js

/**
 * PSEUDOCODE
 * - initialize the left argument to 0
 * - initialize the right argument to array.length
 * - use the pivot helper fn to get the pivot index pivot(array, right, left)
 * - recursively call the quickSort fn on both the left and right side of the pivot index
 * - ONLY if the left is < right index
 * - hence base case should be if (left < right) { keep calling quickSort recursively }
 * - when done return array
*/
function quickSort(array, left=0, right=array.length) {
    if (left < right) {
        const pivotPosition = pivot(array, left, right);
        quickSort(array, left, pivotPosition-1);
        quickSort(array, pivotPosition+1, right);
    }
    
    return array;
}

/**
 * PSEUDOCODE (pivot helper function)
 * - set the pivot element with the start argument
 * - initilize a swap index to be the start argument
 * - start a loop from the next item following item at the start(+1)
 * - position of the array to the item at the end postion of the array
 * - compare each item with the set pivot element
 * - if any item is smaller than the pivot item then
 * - increment the swap index and swap that item with
 * - the pivot element in the array
*/
function pivot(array, start=0, end=array.length-1) {
    let pivotElement = array[start];
    let swapIndex = start;
  
    for (let i = start + 1; i < end; i++) {
      if (array[i] < pivotElement) {
        swapIndex++;
        swap(array, swapIndex, i);
      }
    }
  
    swap(array, swapIndex, start);
}

function swap(array, position1, position2) {
    let temp = array[position1];
    array[position1] = array[position2]
    array[position2] = temp;
}