An flavour of quick-sort I found while reading "The joy of Clojure". In the book, the Clojure implementation was tail-recursive and lazy; this translation has neither of those qualities. It was written to help me understand the Clojure implementation.

sorta-tail-recursive-quick-sort.js

console.log(quickSort([2,1,4,3]));
console.log(quickSort(randomInts(20)));

function randomInts(n) {
  return Array.apply(null, Array(n)).map(() => Math.floor(Math.random() * n));
}

function quickSort(array) {
  return quickSortLists([array]);
}

function quickSortLists(lists) {
  const selectedList = first(lists);
  const otherLists = rest(lists);
  if (isNotEmpty(selectedList)) {
    const pivot = first(selectedList);
    const otherItemsInList = rest(selectedList);
    return quickSortLists([
      otherItemsInList.filter((item) => item < pivot),
      pivot,
      otherItemsInList.filter((item) => item >= pivot),
      ...otherLists
    ]);
  } else if (isNotEmpty(otherLists)) {
    return [ first(otherLists), ...quickSortLists(rest(otherLists)) ];
  } else {
    return [];
  }
}

function isNotEmpty(list) {
  return Array.isArray(list) && list.length !== 0;
}

function first(list) {
  return list[0];
}

function rest(list) {
  return list.slice(1);
}