index.js

import { ref } from "vue";

export default function usePosts() {
  let post = ref({});
  let posts = ref([]);
  let user = ref({});

  function fetchPosts() {
    fetch(`https://jsonplaceholder.typicode.com/posts`)
      .then(response => response.json())
      .then(data => (posts.value = data));
  }

  function fetchPost(postId) {
    fetch(`https://jsonplaceholder.typicode.com/posts/${postId}`)
      .then(response => response.json())
      .then(data => (post.value = data))
      .then(data => fetchUser(data.userId));
  }

  function fetchUser(userId) {
    fetch(`https://jsonplaceholder.typicode.com/users/${userId}`)
      .then(response => response.json())
      .then(data => (user.value = data));
  }

  return { fetchPosts, fetchPost, fetchUser, post, posts, user };
}