Example of refactoring duplicated code

photoUtil.js

// Before

const isUserTagged = (user, photo) => {
  return photo.taggedUsers.map(user => user.id).includes(user.id)
}

const isUserBlocked = (user, photo) => {
  return photo.user.blockedFriends.map(user => user.id).includes(user.id)
}

// After

const isUserIn = (user, userPool) => {
  return userPool.map(user => user.id).includes(user.id);
}

const isUserTagged = (user, photo) => {
  return isUserIn(user, photo.taggedUsers);
}

const isUserTagged = (user, photo) => {
  return isUserIn(user, photo.blockedFriends);
}