function oddOnesOut(nums) {
  let acc = nums.reduce((acc, val) => {acc[val] = 1 + acc[val] || 1; return acc}, {});
  const evens = []
  for (const key of Object.keys(acc)) {
    acc[key] % 2 ? null : evens.push(Number(key))
  }
  return nums.filter(x => evens.includes(x))
}