Three-way partitioning algorithm with ranking function (for JavaScript)

threewaypartition.js

const __valueranking__ = (minvalue, maxvalue = minvalue) => {
  if (maxvalue < minvalue) {
    const temp = minvalue;
    minvalue = maxvalue;
    maxvalue = temp;
  }

  return (value) => +(value >= minvalue ? value > maxvalue : -1);
};
    
const __reverseranking__ = (rankingfn) => (value) => -rankingfn(value);

const __swap__ = (arr, idx1, idx2) => {
  const temp = arr[idx1];
  arr[idx1] = arr[idx2];
  arr[idx2] = temp;
};

const Ranking = Object.create(null, {
  reverse: { value: __reverseranking__ },
  value: { value: __valueranking__ }
});

const threewaypartition = (arr, rankingfn) => {
  let i = 0, j = 0, k = arr.length - 1;

  while (j <= k) {
    const rank = rankingfn(arr[j]);
    if (rank === 0) { j++; continue; }
    rank < 0 ? __swap__(arr, i++, j++) : __swap__(arr, k--, j);
  }

  return [i, k];
};

export { Ranking };
export default threewaypartition;