dex3r

opis.filter((el, i, arr) => arr.indexOf(el) === arr.lastIndexOf(el))

function uniq (arr) {
  const store = arr.reduce((acc, cur) => {
    !acc[cur] ? acc[cur] = 1 : acc[cur]++
    return acc
  }, {})
  return Object.keys(store).filter(key => store[key] === 1)
}