Codility: OddOccurrencesInArray Solution

1function solution(A) {
2  const group = A.reduce((acc, el) => {
3    acc.set(el, (acc.get(el) || 0) + 1)
4    return acc
5  }, new Map())
6  for (const g of group) {
7    if (g[1] % 2 !== 0) {
8      return g[0]
9    }
10  }
11}