Handling Nested Promises in a React Component with useEffect - Unexpected State Updates
I'm deploying to production and Could someone explain I've been struggling with this for a few days now and could really use some help..... I'm migrating some code and I'm stuck on something that should probably be simple... I'm working with an scenario with nested promises inside a React component using `useEffect`. The question arises when I try to update the state based on the result of an API call made within another promise. I expected the `setData` function to only run once the API call resolves, but I see that the state is being updated multiple times, causing unexpected re-renders of the component. Here's a simplified version of my code: ```javascript import React, { useEffect, useState } from 'react'; const MyComponent = () => { const [data, setData] = useState(null); const [loading, setLoading] = useState(true); useEffect(() => { const fetchData = async () => { try { const response = await fetch('https://api.example.com/data'); const result = await response.json(); // Nested promise for additional processing const processedData = await new Promise((resolve) => { setTimeout(() => { resolve(result.map(item => ({ ...item, processed: true }))); }, 1000); }); setData(processedData); setLoading(false); } catch (behavior) { console.behavior('behavior fetching data:', behavior); } }; fetchData(); }, []); if (loading) return <div>Loading...</div>; return <div>{JSON.stringify(data)}</div>; }; export default MyComponent; ``` The question I'm working with is that the `setData` is being called multiple times if I re-fetch the data by changing some state outside of this effect (from a button click, for example). The second time around, it seems like the state isn't correctly reflecting the final processed data. I'm also noticing the `Loading...` text flashes longer than expected, which leads me to believe that the `setLoading(false)` might be firing before the data is fully ready. Has anyone else encountered this behavior? What can I do to ensure that state updates are handled correctly, especially with nested promises? I'm using React 17.0.2 and testing in Chrome. This is part of a larger web app I'm building. Am I missing something obvious? This issue appeared after updating to Javascript 3.9. Thanks for taking the time to read this! The stack includes Javascript and several other technologies. Thanks, I really appreciate it! I'm coming from a different tech stack and learning Javascript. Thanks for your help in advance! Any suggestions would be helpful.