evenOccurrence

문제

Find the first item that occurs an even number of times in an array. Remember to handle multiple even-occurrence items and return the first one. Return null if there are no even-occurrence items.

풀이

var evenOccurrence = function(arr) {
  for (let i = 0; i < arr.length; i++) {
    if (arr.filter(e => e === arr[i]).length % 2 === 0) {
      return arr[i];
    }
  }
};