Group and count "Even - Odd" values

getEvenOddCounts.js

function getEvenOddCounts (acc, val) {
  const key = val % 2 === 0 ? "even" : "odd";
  acc[key] = (acc[key] ?? 0) + 1;
  return acc;
}

const result = [1, 2, 3, 4, 5].reduce(getEvenOddCounts, {});

console.log(result); // { even: 2, odd: 3 }


// even as a "one-liner"

[1, 2, 3, 4, 5].reduce((acc, val) => { const key = val % 2 === 0 ? "even" : "odd"; acc[key] = (acc[key] ?? 0) + 1; return acc