function partition(arr, startIndex, endIndex) {

  const pivotVal = arr[endIndex]; // the pivot element

  let index = startIndex;

  // begin iterate and swap

  for (let i = index; i < endIndex; i++) {

    if (arr[i] < pivotVal) {

      [arr[i], arr[index]] = [arr[index], arr[i]];

      index += 1;

    }

  }

  // move `pivotVal` to the middle index and return middle index

  [arr[index], arr[endIndex]] = [arr[endIndex], arr[index]];

  return index;

}

function quickSort(arr, startIndex, endIndex) {

  // Base case or terminating case

  if (startIndex >= endIndex) {

    return;

  }

  // Returns midIndex / pivot index

  let midIndex = partition(arr, startIndex, endIndex);

  // Recursively apply the same logic to the left and right subarrays

  quickSort(arr, startIndex, midIndex - 1);

  quickSort(arr, midIndex + 1, endIndex);

}

let arr = [-2, 4, 6, 3, 7, 2];

quickSort(arr, 0, arr.length - 1);

console.log(arr); // [-2, 2, 3, 4, 6, 7]