solution for Odd Occurrences in Array Task on Codility

OddOccurrencesInArray.js

function solution(A) {
  var B = [];
  var max = 0;

  for (var i = 0; i < A.length; i++) {
    if (typeof B[A[i]] === "undefined") {
      B[A[i]] = 0;
      if (A[i] > max) max = A[i];
    }
    B[A[i]]++;
  }

  for (var j = 1; j <= max; j++) {
    if (typeof B[j] != "undefined") if (B[j] % 2 != 0) return j;
  }
}