A = [9, 3, 9, 3, 9, 7, 9, 8, 8]

// return the unpaired element

let unpaired = (A) => {

  let unique = new Set(A)

  for (element of unique) {
    let filtered = A.filter(number => number === element);

    if (filtered.length % 2 === 1) {
      return element
    }

  }

}

unpaired(A)