quick_sort.js

function quickSort(items, leftIndex, rightIndex) {
  // Declare an index that will be our pivot reference.
  var pivotIndex;

  // If the array has only one item, it's already sorted!
  // If it has no items, we don't want to try to sort it!
  if (items.length > 1) {
    // As long as the array has two items, we can parition it.
    pivotIndex = partition(items, leftIndex, rightIndex);

    console.log('** pivot is: ', items[pivotIndex]);

    // If the left reference hasn't been incremented to
    // reach the pivot yet, we want to keep comparing it.
    if (leftIndex < pivotIndex - 1) {
      quickSort(items, leftIndex, pivotIndex - 1);
    }

    // If the right reference hasn't reached the 
    // pivotIndex yet, we need to keep comparing it.
    if (pivotIndex < rightIndex) {
      quickSort(items, pivotIndex, rightIndex);
    }

  }

  return items;
}

Actually, the length of items will always be greater than one... Should produce a stack overflow... I guess you wanted to write leftIndex < rightIndex in line 7