function fetchCatAvatars(userId) {
  return fetch(`https://catappapi.herokuapp.com/users/${userId}`)
    .then(response => response.json())
    .then(user => {
      const promises = user.cats.map(catId => 
        fetch(`https://catappapi.herokuapp.com/cats/${catId}`)
          .then(response => response.json())
          .then(catData => catData.imageUrl))
      return Promise.all(promises)
    })
}