JavaScript の配列から奇数に出現した数値/要素を削除する

const arr = [1, 6, 3, 1, 3, 1, 6, 3];

const output = [1, 6, 3, 1, 3, 6];

const arr = [1, 6, 3, 1, 3, 1, 6, 3];
const removeOddOccurence = (arr =[]) => {
   // keeping the original array unaltered
   const copy = arr.slice();
   const map = {};
   arr.forEach((num, ind) => {
      if(map.hasOwnProperty(num)){
         map[num][0]++;
         map[num][1] = ind;
      }else{
         map[num] = [1, ind];
      };
   });
   for(const key in map){
      const [freq, index] = map[key];
      if(freq !== 1 && freq % 2 === 1){
         copy.splice(index, 1, '');
      };
   };
   return copy.filter(el => el !== '');
};
console.log(removeOddOccurence(arr));