stats.js

exports.max = (numbers) => Math.max(...numbers);

exports.min = (numbers) => Math.min(...numbers);

// exports.avg = (numbers) =>
//   numbers.reduce(
//     (acc, current, index, array) =>
//       index === array.length - 1
//         ? (acc + current) / array.length
//         : acc + current,
//     0
//   );

exports.avg = (numbers) =>
  numbers.reduce(
    (acc, current, index, { length }) => acc + current / length,
    0
  );

exports.sort = (numbers) => numbers.sort((a, b) => a - b);

exports.median = (numbers) => {
  const { length } = numbers;
  const middle = Math.floor(length / 2);
  return length % 2
    ? numbers[middle]
    : (numbers[middle - 1] + numbers[middle]) / 2;
};

exports.mode = (numbers) => {
  const counts = numbers.reduce(
    (acc, current) => acc.set(current, acc.get(current) + 1 || 1),
    new Map()
  );

  const maxCount = Math.max(...counts.values());
  const modes = [...counts.keys()].filter(
    (number) => counts.get(number) === maxCount
  );

  if (modes.length === numbers.length) {
    return null;
  }

  if (modes.length > 1) {
    return modes;
  }

  return modes[0];
};