quicksort

quicksort.js

function quicksort(arr, comp0) {
  if (arr.length <= 1) {
    return arr;
  }

  const comp = comp0 ? comp0 : (a, b) => parseInt(a) - parseInt(b);

  const pivot = arr[0];
  const higher = [];
  const lower = [];

  arr.slice(1).forEach(val => (comp(val, pivot) > 0) ? higher.push(val) : lower.push(val));

  return [
    ...quicksort(lower, comp),
    pivot,
    ...quicksort(higher,comp)
  ];
}

quicksort.php

function quicksort(array $arr, callable $comp = null)
{
    if (count($arr) <= 1) {
        return $arr;
    }

    $comp = $comp ?: function ($a, $b) {
        return intval($a) - intval($b);
    };

    $pivot = $arr[0];
    $lower = $higher = [];

    foreach (array_slice($arr, 1) as $val) {
        if ($comp($pivot, $val) > 0) {
            $lower[] = $val;
        } else {
            $higher[] = $val;
        }
    }

    return array_merge(
        quicksort($lower, $comp),
        [$pivot],
        quicksort($higher, $comp)
    );
}