<!DOCTYPE html>
Mastering useEffect: Beware of depending on values you set
When working with React, the useEffect hook is a powerful tool for managing side effects in your components. However, one common pitfall that developers encounter is depending on values that are set within the useEffect callback itself. This can lead to unexpected behavior and bugs in your application. Let’s dive into why this happens and how to avoid it.
When you set a value inside the useEffect callback, it may not be immediately available in subsequent renders. This is because useEffect runs after every render, so the value may not have been updated yet. If you depend on this value in another part of your component, it could lead to inconsistent behavior.
One way to avoid this issue is to use the useRef hook to store the value instead. useRef allows you to create a mutable object that persists between renders, so you can safely set and access values without worrying about timing issues.
Here’s an example of how you can refactor your code to use useRef instead:
“`javascript
import { useEffect, useRef } from ‘react’;
const MyComponent = () => {
const myValueRef = useRef(null);
useEffect(() => {
myValueRef.current = ‘myValue’;
}, []);
useEffect(() => {
console.log(myValueRef.current);
}, []);
return (
My Component
);
};
“`
By using useRef to store the value, you can ensure that it will be available when you need it, without running into timing issues. This can help you avoid bugs and maintain a more predictable state in your components.
In conclusion, when working with useEffect, be cautious of depending on values that you set within the callback. Instead, consider using useRef to store values that need to persist between renders. This will help you avoid unexpected behavior and ensure a more robust and reliable application.
Should be spending more time in the docs. I wasted lots of time by using direct update and not utilizing the clean-up functions. Thanks so much for this.
just pasted a screenshot of the initial code into chatgpt and it suggested the correct revised code!
Shouldn’t count be set as a dependency?
I did not quite understand what the return function of a `useEffect` hook was supposed to do. Now I do, and I have always needed it without even knowing. 😀😆
Thank you.
useEffect a knife for monkeys
This is great. Is there a way to save these shorts for quick reference?
I just saw a similar bug today in a friend's code.
He is using firebase for auth and realtime database snapshots in a WhatsApp clone he's building.
In one useEffect we are creating a snapshot listener with zero dependencies.
The snapshots callback does not run until the current user is set
In another useEffect we are updating the current user state variable
The user is set to current user but the snapshot listener forms a closure with the stale state variable and nothing happens even though the snapshot callback is being invoked
The cleanup function doesn't cause any re-render, which means the component will no longer update any state. So How does the callback function runs again even we didn't watch for any changes?
Thanks for so much Jack!!
What's the theme and style of your vscode!
Once spent like 5 hours trying to find a way to solve EXACTLY this problem until i finally poured through the docs to find the functional setState method.
It’s way more predictable in Angular
What is meant here by a "stale closure"?
setInterval and setTimeout on React have been always messy to implement. Every time I need to work with those methods, I need to be very careful because it's not intuitive for remembering. I don't like React mental model cause of that, so for personal projects I'm moving to SolidJS, where timer methods become intuitive again.
This has bitten me a few times 😀
"beware of depending on values that you set" also sounds like some eastern philosophy