React - advanced patterns when using useEffect with array dependencies and dynamic state updates
I'm reviewing some code and I've searched everywhere and can't find a clear answer... I'm working through a tutorial and I'm working on a project and hit a roadblock. Quick question that's been bugging me - I'm working with an scenario with the `useEffect` hook in my React application while trying to manage a state array... I have a component where I need to fetch user data based on an array of user IDs. The question arises when I update the array of user IDs; the `useEffect` seems to trigger an unexpected number of times, leading to multiple API calls and performance optimization. Here's a simplified version of my code: ```javascript import React, { useEffect, useState } from 'react'; const UserList = () => { const [userIds, setUserIds] = useState([1, 2, 3]); const [users, setUsers] = useState([]); useEffect(() => { const fetchUsers = async () => { const userPromises = userIds.map(id => fetch(`https://jsonplaceholder.typicode.com/users/${id}`)); const userResponses = await Promise.all(userPromises); const userData = await Promise.all(userResponses.map(res => res.json())); setUsers(userData); }; fetchUsers(); }, [userIds]); const addUserId = (newId) => { setUserIds((prev) => [...prev, newId]); // Dynamic update to userIds }; return ( <div> <button onClick={() => addUserId(userIds.length + 1)}>Add User ID</button> <ul>{users.map(user => <li key={user.id}>{user.name}</li>)}</ul> </div> ); }; export default UserList; ``` When I click the button to add a new user ID, the `useEffect` runs, which is expected. However, it runs multiple times for a single update, causing multiple fetches. I see this in the network tab as well. I'm using React 17.0.2 and the latest version of React Router. Is there a reason why it triggers multiple times, or is there a best practice that I'm missing? I want to ensure that it only fetches data once for each set of user IDs, and not every time the state updates. Any help or guidance would be appreciated! Any help would be greatly appreciated! Any ideas what could be causing this? I recently upgraded to Javascript stable. I'm open to any suggestions. Thanks for taking the time to read this! This is for a desktop app running on Linux. Any examples would be super helpful.