Quick Sort implemented in JS

javascript-qiucksort.js

function quickSort(array, left = 0, right = array.length - 1) {
  console.log("CALLED");
  let partitionIndex;
  let pivotIndex;
  if(left < right) {
    pivotIndex = right;
    partitionIndex = partition(array, left, right, pivotIndex);
    quickSort(array, left, partitionIndex - 1);
    quickSort(array, partitionIndex + 1, right);
  }
  return array;
}

function partition(a, left, right, pivotIndex) {
  let partitionIndex = left,
      pivot = array[pivotIndex];
  for(let i = left; i < right; i++) {
    if(a[i] < pivot) {
      [a[i], a[partitionIndex]] = [a[partitionIndex], a[i]];
      partitionIndex += 1
    }
  }
  [a[right], a[partitionIndex]] = [a[partitionIndex], a[right]];
  return partitionIndex;
}