const voter = {};
const checkVoter = (vote) => {
  if (voter[vote]) {
    console.log('Duplicate', vote);
    return false;
  }

  voter[vote] = true;
  console.log('Success Vote', vote);
  return true;
}


checkVoter('Mike');
checkVoter('Jack');
checkVoter('John');
checkVoter('Mike');