Int의 1000 단위마다 ',' 찍어주는 코드

const everyThousand = (num) => {
  const arr = String(num).split('');
  let indexChecker = arr.length - 1;
  let count = 0;
  while (indexChecker > 0) {
    count ++;
    indexChecker --;
    if (count % 3 === 0) {
      arr.splice(indexChecker + 1, 0, ',');
    };
  };
  return arr.join('');
};