Implementing Quicksort in JavaScript

setup.js

const quickSort = (
  unsortedArray,
  comparator = defaultComparator
) => {

  // Create a sortable array to return.
  const sortedArray = [...unsortedArray];

  // Recursively sort sub-arrays.
  const recursiveSort = (start, end) => {

    // If this sub-array is empty, it's sorted.
    if (end - start < 1) {
      return;
    }
    const pivotValue = sortedArray[end];
    let splitIndex = start;
  };

  // Sort the entire array.
  recursiveSort(0, unsortedArray.length - 1);
  return sortedArray;
};