March 27, 2023 rAbhiszek EH9 minutes of reading
Content
You may have seen the following warning appear randomly in the browser console whenever you debug a React application:
Warning: You cannot perform a React state update on an unmounted component. This is not an operation, but it does indicate a memory leak in your application. To fix this, cancel all subscriptions and async tasks in the useEffect cleanup function.
Have you ever wondered why this happens?
This happens in the following scenario:
- You are making an asynchronous call (eg network call) within a component.
- The calling component is unmounted due to some user action (for example, user exit).
- The async connection responds and you have it
define statecall the success handler.
In the above case, React tries to set the state of the unmounted component, which is not necessary as the component is no longer in scope. Then React warns us that there is a piece of code that tries to update the state of an unmounted component. component. As React suggests, this won't cause any errors in your app, but it might take up unnecessary memory.
In this article, we will look at different scenarios where this error can occur and how we can fix them.
looking for calls
Consider the following code:
DownloadPosts.js
1matter {UseEffect,state of use} z "to react"
2
3until Download posts = () => {
4 until [posts,set posts] = state of use([])
5 UseEffect(() => {
6 until download data = asynchronous () => {
7 to try {
8 untilresponder= Wait for recover(
9 „https://jsonplaceholder.typicode.com/posts”
10 )
11 console.Daily("response received")
12 untilDanish= Wait forresponder.json()
13 set posts(Danish)
14 } to take (mi) {
15 console.Daily(mi)
16 }
17 }
18
19 download data()
20 }, [])
21 turn back (
22 <ul>
23 {posts.map(post => {
24 turn back <li key={post.I WENT}>{post.title}li>
25 })}
26 ul>
27 )
28}
29
30export standard Download posts
Here, when the component is assembled, we call the methodJSON placeholderAPI and listing posts.
Now attach the component to the fileApplicationHey:
app.js
1matter to react, {state of use} z "to react"
2matter Download posts z "./Download Posts"
3
4function Application() {
5 until [mostrarPosts,setShowPosts] = state of use()
6
7 turn back (
8 <dz>
9 <button when clicking={() => setShowPosts(TRUE)}>Download postsbutton>
10 <button when clicking={() => setShowPosts(FALSEHOOD)}>hide postsbutton>
11 {mostrarPosts&& <Download posts />}
12 dz>
13 )
14}
15
16export standard Application
Now, if you run the code and click "Get Posts" and then click "Hide Posts", even before you get a response, you will see the message log (even though the component is unmounted) and a warning in the console:
You can set the limitation to slow 3G if the reply comes quickly and you can't click "Hide Posts" in time.
How to resolve this notice?
There is an interface calledinterrupt controllerwhich helps in canceling network requests whenever the user needs it.
DownloadPosts.js
1matter {UseEffect,state of use} z "to react"
2
3until Download posts = () => {
4 until [posts,set posts] = state of use([])
5 UseEffect(() => {
6 untilcontroller= novo interrupt controller()
7 untilsignal=controller.signal
8 until download data = asynchronous () => {
9 to try {
10 untilresponder= Wait for recover(
11 „https://jsonplaceholder.typicode.com/posts”,
12 {
13 signal:signal,
14 }
15 )
16 console.Daily("response received")
17 untilDanish= Wait forresponder.json()
18 set posts(Danish)
19 } to take (mi) {
(Video) "Cannot update unmounted components" warning with React's Hooks20 console.Daily(mi)
21 }
22 }
23
24 download data()
25
26 turn back () => {
27controller.cancel()
28 }
29 }, [])
30 turn back (
31 <ul>
32 {posts.map(post => {
33 turn back <li key={post.I WENT}>{post.title}li>
34 })}
35 ul>
36 )
37}
38
39export standard Download posts
As you can see in the above code, we are accessing the fileabort signand pass it to the download request. Each time the component is unmounted, we cancel the request (in the callbackUseEffect).
Axios Summon
let's rewriteDownload postscomponent to useosi.
Make sure you have installed axios with the following command (or usenpm e axios):
1fio to addosi
Now use it onAxiosPostyNameHey:
AxiosPosts.js
1matter osi z „osi”
2matter {UseEffect,state of use} z "to react"
3
4export until AxiosPostyName = () => {
5 until [posts,set posts] = state of use([])
6 UseEffect(() => {
7 until download data = asynchronous () => {
8 to try {
9 untilresponder= Wait forosi.to take(
10 „https://jsonplaceholder.typicode.com/posts”
11 )
12 console.Daily("response received")
13 untilDanish=responder.Danish
14 set posts(Danish)
15 } to take (mi) {
16 console.Daily(mi)
17 }
18 }
19
20 download data()
21 }, [])
22 turn back (
23 <ul>
24 {posts.map(post => {
25 turn back <li key={post.I WENT}>{post.title}li>
26 })}
27 ul>
28 )
29}
30
31export standard AxiosPostyName
Now if you includeAxiosPostyNamein the application component and click "Get Posts" and "Hide Posts" before getting a response, you will see a warning.
To cancel previous requests in React, axios has something calledCancelToken.on myprevious article, I explained in detail how to cancel previous requests in axios. We'll use the same logic here.
AxiosPosts.js
1matter osi z „osi”
2matter {UseEffect,state of use} z "to react"
3
4export until AxiosPostyName = () => {
5 until [posts,set posts] = state of use([])
6 UseEffect(() => {
7 to allowcancelToken
8
9 until download data = asynchronous () => {
10cancelToken=osi.CancelToken.source()
11 to try {
12 untilresponder= Wait forosi.to take(
13 „https://jsonplaceholder.typicode.com/posts”,
14 { cancelToken:cancelToken.signal }
15 )
16 console.Daily("response received")
17 untilDanish=responder.Danish
18 set posts(Danish)
19 } to take (mi) {
20 console.Daily(mi)
21 }
22 }
23
24 download data()
25
26 turn back () => {
27cancelToken.cancel("Operation cancelled.")
28 }
(Video) React Tips - Fix: Can't perform a React state update on an unmounted component29 }, [])
30 turn back (
31 <ul>
32 {posts.map(post => {
33 turn back <li key={post.I WENT}>{post.title}li>
34 })}
35 ul>
36 )
37}
38
39export standard AxiosPostyName
As for the axiomsv0.22.0,CancelTokenit is deprecated and it is recommended to use itinterrupt controllerhow we use inrecoverconnections. This is how the code would look if we were usinginterrupt controller:
AxiosPosts.js
1matter osi z „osi”
2matter {UseEffect,state of use} z "to react"
3
4export until AxiosPostyName = () => {
5 until [posts,set posts] = state of use([])
6 UseEffect(() => {
7 untilcontroller= novo interrupt controller()
8 untilsignal=controller.signal
9
10 until download data = asynchronous () => {
11 to try {
12 untilresponder= Wait forosi.to take(
13 „https://jsonplaceholder.typicode.com/posts”,
14 {
15 signal:signal,
16 }
17 )
18 console.Daily("response received")
19 untilDanish=responder.Danish
20 set posts(Danish)
21 } to take (mi) {
22 console.Daily(mi)
23 }
24 }
25
26 download data()
27
28 turn back () => {
29controller.cancel()
30 }
31 }, [])
32 turn back (
33 <ul>
34 {posts.map(post => {
35 turn back <li key={post.I WENT}>{post.title}li>
36 })}
37 ul>
38 )
39}
40
41export standard AxiosPostyName
chamadas setTimeout
set time limitis another async call where we would find this warning.
Consider the following component:
timeout.js
1matter to react, {UseEffect,state of use} z "to react"
2
3until stopwatch = () => {
4 until [message,set message] = state of use("Starting the Timer")
5 UseEffect(() => {
6 set time limit(() => {
7 set message("End of time!")
8 }, 5000)
9 }, [])
10 turn back <dz>{message}dz>
11}
12
13until End of time = () => {
14 until [show timer,define ShowTimer] = state of use(FALSEHOOD)
15 turn back (
16 <dz>
17 <button when clicking={() => define ShowTimer(!show timer)}>toggle timerbutton>
18 <dz>{show timer&& <stopwatch />}dz>
19 dz>
20 )
21}
22
23export standard End of time
Here we have a state with an initial value of "Timer Running" which will be set to "Times Up!" after 5 seconds. If you change the timer before the time limit expires, you will receive a warning.
We can fix it by callingclear timeouton the timeout id returned byset time limitcall as below:
timeout.js
1matter to react, {UseEffect,use Ref,state of use} z "to react"
2
3until stopwatch = () => {
4 until [message,set message] = state of use("Starting the Timer")
5 // reference used so it doesn't change during rendering
(Video) Cannot Perform State Update on an Unmounted Component [Solved using Custom Hook]6 to allowtimeout id= use Ref(zero)
7 UseEffect(() => {
8timeout id.current = set time limit(() => {
9 set message("End of time!")
10 }, 5000)
11
12 turn back () => {
13 clear timeout(timeout id.current)
14 console.Daily("clean timeout")
15 }
16 }, [])
17 turn back <dz>{message}dz>
18}
19
20until End of time = () => {
21 until [show timer,define ShowTimer] = state of use(FALSEHOOD)
22 turn back (
23 <dz>
24 <button when clicking={() => define ShowTimer(!show timer)}>toggle timerbutton>
25 <dz>{show timer&& <stopwatch />}dz>
26 dz>
27 )
28}
29
30export standard End of time
setInterval calls
Like setTimeout, we can fix the warning by callingclear rangeat any timeUseEffectcleanup function is called:
interval.js
1matter to react, {UseEffect,use Ref,state of use} z "to react"
2
3until Countdown = () => {
4 until [remaining,define Remaining] = state of use(10)
5 // reference used so it doesn't change during rendering
6 to allowrange id= use Ref(zero)
7 UseEffect(() => {
8 Se (!range id.current) {
9range id.current = set interval(() => {
10 console.Daily("interval")
11 define Remaining(existing value =>
12existing value> 0 ?existing value- 1 :existing value
13 )
14 }, 1000)
15 }
16 turn back () => {
17 clear range(range id.current)
18 }
19 }, [])
20 turn back <dz>Time left:{remaining}Sdz>
21}
22
23until Interval = () => {
24 until [show timer,define ShowTimer] = state of use(FALSEHOOD)
25 turn back (
26 <dz>
27 <button when clicking={() => define ShowTimer(!show timer)}>toggle timerbutton>
28 <dz>{show timer&& <Countdown />}dz>
29 dz>
30 )
31}
32
33export standard Interval
event listeners
Event listeners are another example of asynchronous calls. Let's say there's a box and you want to check if the user has clicked inside or outside the box. So, as described inone of my previous articles, we'll bind the onClick listener to the document and check whether the click triggers on the field or not:
DocumentClick.js
1matter to react, {UseEffect,use Ref,state of use} z "to react"
2
3until Box = () => {
4 untilref= use Ref(zero)
5 until [position,defined position] = state of use("")
6
7 UseEffect(() => {
8 until make sure you clicked off = mi => {
9 Se (ref.current &&ref.current.contains(mi.O)) {
10 defined position("inside")
11 } otherwise {
12 defined position("in addition to")
13 }
14 }
15 document.addEventListener("clique",make sure you clicked off)
16 }, [])
17
18 turn back (
19 <>
20 <dz>{position? `clicked${position}` : "Click somewhere"}dz>
21 <dz
22 ref={ref}
23 style={{
24 width: "200 pixels",
25 height: "200 pixels",
26 border: "1 solid pixel",
27 }}
28 >dz>
29 >
(Video) Résoudre l'erreur Can't perform a React state update on an unmounted component30 )
31}
32
33until click on the document = () => {
34 until [show box,set ShowBox] = state of use(FALSEHOOD)
35 turn back (
36 <>
37 <dz
38 style={{
39 Show: "wire",
40 justify the content: "Center",
41 align the elements: "Center",
42 flex Kierunek: "column",
43 height: „100vh”,
44 }}
45 >
46 <button
47 style={{ marginInferior: "1 Thing" }}
48 when clicking={() => set ShowBox(!show box)}
49 >
50switch box
51 button>
52 {show box&& <Box />}
53 dz>
54 >
55 )
56}
57
58export standard click on the document
Now, if you click on "Toggle Box", a window will appear. If you click anywhere, the message will change depending on where you clicked. If you now hide the field by clicking "Toggle Field" and clicking anywhere in the document, you will see a warning in the console.
You can fix it by callingremove event listenerwhileUseEffectto clean:
DocumentClick.js
1matter to react, {UseEffect,use Ref,state of use} z "to react"
2
3until Box = () => {
4 untilref= use Ref(zero)
5 until [position,defined position] = state of use("")
6
7 UseEffect(() => {
8 until make sure you clicked off = mi => {
9 Se (ref.current &&ref.current.contains(mi.O)) {
10 defined position("inside")
11 } otherwise {
12 defined position("in addition to")
13 }
14 }
15 document.addEventListener("clique",make sure you clicked off)
16 turn back () => {
17 document.remove event listener(make sure you clicked off)
18 }
19 }, [])
20
21 turn back (
22 <>
23 <dz>{position? `clicked${position}` : "Click somewhere"}dz>
24 <dz
25 ref={ref}
26 style={{
27 width: "200 pixels",
28 height: "200 pixels",
29 border: "1 solid pixel",
30 }}
31 >dz>
32 >
33 )
34}
35
36until click on the document = () => {
37 until [show box,set ShowBox] = state of use(FALSEHOOD)
38 turn back (
39 <>
40 <dz
41 style={{
42 Show: "wire",
43 justify the content: "Center",
44 align the elements: "Center",
45 flex Kierunek: "column",
46 height: „100vh”,
47 }}
48 >
49 <button
50 style={{ marginInferior: "1 Thing" }}
51 when clicking={() => set ShowBox(!show box)}
52 >
53switch box
54 button>
55 {show box&& <Box />}
56 dz>
57 >
58 )
59}
60
61export standard click on the document
source code
You can see the full source codeHere.
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FAQs
Unable to perform react state update on unmounted component | CodingDeft.com? ›
The error: “Can't perform a react state update on an unmounted component” tells us that we are trying to modify a component's state after the component is unmounted. In simple words, React has removed the component from the VDOM (Virtual DOM) and from the real DOM, and still, we are trying to change its state.
Why can t we update the React component state directly? ›The state of a component is managed internally by React. Updating the state of a component directly can have unintended consequences that can be difficult to debug. If the state is updated directly as in the example above, the component will not rerender since the state is compared shallowly.
Why is React not updating on state change? ›State updates in React are asynchronous; when an update is requested, there is no guarantee that the updates will be made immediately. The updater functions enqueue changes to the component state, but React may delay the changes, updating several components in a single pass.
What is setting state on unmounted component in React? ›Summary. Seeing called setState() on an unmounted component in your browser console means the callback for an async operation is still running after a component's removed from the DOM.
How do I update the state component in Reactjs? ›To change a value in the state object, use the this. setState() method. When a value in the state object changes, the component will re-render, meaning that the output will change according to the new value(s).
Can we update state without setState? ›In other words, if we update state with plain JavaScript and not setState , it will not trigger a re-render and React will not display those (invalid) changes in state to our user. This is a simple, but crucial lesson to remember.
Which is the correct way to update the property of React state? ›When the React state is mutated directly, Reactjs does not re-render the reflect the state change. The correct way to update the name and age is to use the spreader operator and the useState-provided setter method.
Why is my useState not updating on render? ›When the “useState” set method is not reflecting a change immediately, it may be due to the current closure of the state variable. Hence, it is still referring to the old value of the state. It is the failure of the re-render to reflect the updated value of the state.
What is the correct way to update a state in React application and why? ›The setState() Method
State can be updated in response to event handlers, server responses, or prop changes. This is done using the setState() method. The setState() method enqueues all of the updates made to the component state and instructs React to re-render the component and its children with the updated state.
Syntax of setState
To make the state change, React gives us a setState function that allows us to update the value of the state. Calling setState automatically re-renders the entire component and all its child components.
What happens when a component is unmounted? ›
During the VirtualDOM Reconciliation if a component existed but no longer will, the component is considered unmounted and given a chance to clean up (via componentWillUnmount ). When tearing down a tree, old DOM nodes are destroyed. Component instances receive componentWillUnmount().
What happens when a React component unmounts? ›React performs the cleanup when the component unmounts.
What does unmounted mean in React? ›The term "mount" tells us that these components are loaded or rendered in the DOM. These are many top-level APIs and methods dealing with this. To make it simple, mounted means the component has been loaded to the DOM and unmounted means the components has been removed from the DOM.
Why setState is not working in React? ›Whenever state needs to be calculated based on a previous state, it's unsafe to pass an object to setState() . Because this. state is updated asynchronously, and changes to state can't be expected to immediately reflect in this.
How do I update a state from one component to another? ›- class ParentComponent extends React.Component { state = { ...
- function ChildComponent(props) { return <div>{props.data}</div>; ...
- const MyContext = React. ...
- function ChildComponent() { ...
- class ParentComponent extends React. ...
- function ChildComponent(props) {
React components automatically re-render whenever there is a change in their state or props. A simple update of the state, from anywhere in the code, causes all the User Interface (UI) elements to be re-rendered automatically.
How do I Rerender a component without setState? ›How can you force react components to rerender without calling the set state? React components re-render on their own whenever there are some changes in their props or state. Simply updating the state, from a random place in the code, causes the User Interface (UI) elements that get re-rendered automatically.
What is the difference between setState and replaceState? ›What is the difference between `setState()` and `replaceState()` methods? When you use setState() the current and previous states are merged. replaceState() throws out the current state, and replaces it with only what you provide.
Why putting setState () in render () is not preferred? ›In constructor , we should avoid using setState() because this is the only place we directly assign the initial state to this. state . Also, we cannot directly put it in render() either since changing state each time triggers re-rendering which calls setState() again. This will result in an infinite loop.
How do you update state in React using hooks? ›To update the state, call the state updater function with the new state setState(newState) . Alternatively, if you need to update the state based on the previous state, supply a callback function setState(prevState => newState) .
How do I update state in React using Redux? ›
The only way to update a state inside a store is to dispatch an action and define a reducer function to perform tasks based on the given actions. Once dispatched, the action goes inside the reducer functions which performs the tasks and return the updated state to the store. This is what Redux is all about.
Which is the best way of state management in React? ›- useState.
- useReducer.
- useMemo & useCallback.
- useEffect.
- useRef.
- Context and Custom Hooks.
- React Query & React Location.
- Zustand.
Forcing an update on a React class component
In any user or system event, you can call the method this. forceUpdate() , which will cause render() to be called on the component, skipping shouldComponentUpdate() , and thus, forcing React to re-evaluate the Virtual DOM and DOM state.
The Redux state is just a regular JavaScript object. When an action has been dispatched, Redux checks if the state has changed or not. If it has not changed then it doesn't have to update the components.
What happens after the component state is being updated in react JS? ›setState() schedules an update to a component's state object. When state changes, the component responds by re-rendering.
How do you refresh a component in React without reloading page? ›window.location.reload(false); This method takes an optional parameter which by default is set to false. If set to true, the browser will do a complete page refresh from the server and not from the cached version of the page.
How does React determine when to update a component? ›React schedules a render every time the state of a component changes. Scheduling a render means that this doesn't happen immediately. React will try to find the best moment for this. Changing the state means that React triggers an update when we call the setState function (in React hooks, you would use useState ).
Is used to update the component manually? ›forceUpdate()
This method allows us to update the component manually.
The only way to update a state inside a store is to dispatch an action and define a reducer function to perform tasks based on the given actions. Once dispatched, the action goes inside the reducer functions which performs the tasks and return the updated state to the store. This is what Redux is all about.
Why is useState not updating state at all? ›If you find that useState / setState are not updating immediately, the answer is simple: they're just queues. React useState and setState don't make changes directly to the state object; they create queues to optimize performance, which is why the changes don't update immediately.