在数组中查找重复项的JavaScript函数将结果打印两次。如何修复？

function findDuplicates(arr) {
  var set = new Set();
  var duplicates = [];

  for (var i = 0; i < arr.length; i++) {
    var num = arr[i];
    if (set.has(num)) {
      duplicates.push(num);
    } else {
      set.add(num);
    }
  }

  return duplicates;
}

var arr = [1, 2, 3, 4, 4, 5, 6, 6];
var result = findDuplicates(arr);
console.log(result); // [4, 6]

function findDuplicates(arr) {
  var obj = {};
  var duplicates = [];

  for (var i = 0; i < arr.length; i++) {
    var num = arr[i];
    if (obj[num]) {
      duplicates.push(num);
    } else {
      obj[num] = true;
    }
  }

  return duplicates;
}

var arr = [1, 2, 3, 4, 4, 5, 6, 6];
var result = findDuplicates(arr);
console.log(result); // [4, 6]