// return promise
{
  //...
  data() {
    return new Promise((resolve) => {
      fetch('some/path')
        .then(res => res.json())
        .then(user => resolve({ user }))
    });
  },
}

// or same with async-await
{
  //...
  async data() {
    const user = await fetch('some/path').then(res => res.json());
    return {
      user,
    };
  },
  ...
}