const a = 1, b = 2, c = 3, d = 4
const [ab, cd] = [a,b,c,d].partition((_, index) => index >= 2)
const [ac, bd] = [a,b,c,d].partition(value => value % 2 === 0)

function quickSort([p, ...tail]) {
  if (!tail.length) return [p, ...tail]
  const [l, r] = tail.partition(x => x > p)
  return [...quickSort(l), p, ...quickSort(r)]
}

quickSort([5, 2, 3, -1])

// not trivial
function partition(arr, callback) {
  return arr.reduce((result, value, index, array) => {
    result[callback(value, index, array) ? 1 : 0].push(value);
    return result;
  }, [[], []]);
}

// not efficient (twice linear scan)
function partition(arr, callback) {
  return [
    arr.filter((...args) => !callback(...args)),
    arr.filter(callback)
  ];
}

function partition(arr, callback) {
  return [
    arr.filterOut(callback),
    arr.filter(callback)
  ];
}