React 18: implementing displaying nested data after updates from multiple sources
I'm prototyping a solution and I'm building a feature where I'm working with a scenario when trying to render nested data in my React 18 application after fetching updates from two different sources... I have a list of users, and each user has a list of posts. When I fetch the users and their posts, I want to update the state accordingly, but it seems that the rendering doesn't trigger as expected. Here’s a simplified version of my code: ```javascript import React, { useEffect, useState } from 'react'; const UserPosts = () => { const [users, setUsers] = useState([]); const [posts, setPosts] = useState([]); useEffect(() => { const fetchUsers = async () => { const response = await fetch('https://api.example.com/users'); const data = await response.json(); setUsers(data); }; const fetchPosts = async () => { const response = await fetch('https://api.example.com/posts'); const data = await response.json(); setPosts(data); }; fetchUsers(); fetchPosts(); }, []); return ( <div> {users.map(user => ( <div key={user.id}> <h2>{user.name}</h2> <ul> {posts .filter(post => post.userId === user.id) .map(post => ( <li key={post.id}>{post.title}</li> ))} </ul> </div> ))} </div> ); }; export default UserPosts; ``` The scenario I'm working with is that the posts only render correctly when I refresh the page. Initially, it seems like the `posts` state is set after the `users` state, which causes the posts to be empty when rendering the users for the first time. I’ve tried adding a loading state, but I’m still working with the same scenario. Here’s my current loading state implementation: ```javascript const [loading, setLoading] = useState(true); useEffect(() => { const fetchData = async () => { setLoading(true); await fetchUsers(); await fetchPosts(); setLoading(false); }; fetchData(); }, []); ``` However, this doesn't seem to help with the rendering of the posts. I also get a warning in the console about "want to read property 'userId' of undefined" because the posts array is initially empty. How can I ensure that my components are rendering the nested data correctly after the fetch operations are complete? Any advice would be much appreciated. This is happening in both development and production on Linux. Thanks for your help in advance!