code.js

async function getUsersData(regionCode) {
  const promiseArray = getUsersIdList(regionCode).map(fetchUserData);

  return Promise.all(promiseArray);
}

async function getPostsData(regionCode) {
  const usersData = await getUsersData(regionCode);
  const promiseArray = usersData
    .map(getPostsIds)
    .reduce((a, b) => a.concat(b))
    .map(fetchPostData);

  return Promise.all(promiseArray);
}