When fetching data I'm getting: Can't perform a React state update on an unmounted component. The app still works, but react is suggesting I might be causing a memory leak.
This is a no-op, but it indicates a memory leak in your application. To fix, cancel all subscriptions and asynchronous tasks in a useEffect cleanup function."
Why do I keep getting this warning?
I tried researching these solutions:
https://developer.mozilla.org/en-US/docs/Web/API/AbortSignal
https://developer.mozilla.org/en-US/docs/Web/API/AbortController
but this still was giving me the warning.
const ArtistProfile = props => {
const [artistData, setArtistData] = useState(null)
const token = props.spotifyAPI.user_token
const fetchData = () => {
const id = window.location.pathname.split("/").pop()
console.log(id)
props.spotifyAPI.getArtistProfile(id, ["album"], "US", 10)
.then(data => {setArtistData(data)})
}
useEffect(() => {
fetchData()
return () => { props.spotifyAPI.cancelRequest() }
}, [])
return (
<ArtistProfileContainer>
<AlbumContainer>
{artistData ? artistData.artistAlbums.items.map(album => {
return (
<AlbumTag
image={album.images[0].url}
name={album.name}
artists={album.artists}
key={album.id}
/>
)
})
: null}
</AlbumContainer>
</ArtistProfileContainer>
)
}
Edit:
In my api file I added an AbortController() and used a signal so I can cancel a request.
export function spotifyAPI() {
const controller = new AbortController()
const signal = controller.signal
// code ...
this.getArtist = (id) => {
return (
fetch(
`https://api.spotify.com/v1/artists/${id}`, {
headers: {"Authorization": "Bearer " + this.user_token}
}, {signal})
.then(response => {
return checkServerStat(response.status, response.json())
})
)
}
// code ...
// this is my cancel method
this.cancelRequest = () => controller.abort()
}
My spotify.getArtistProfile() looks like this
this.getArtistProfile = (id,includeGroups,market,limit,offset) => {
return Promise.all([
this.getArtist(id),
this.getArtistAlbums(id,includeGroups,market,limit,offset),
this.getArtistTopTracks(id,market)
])
.then(response => {
return ({
artist: response[0],
artistAlbums: response[1],
artistTopTracks: response[2]
})
})
}
but because my signal is used for individual api calls that are resolved in a Promise.all I can't abort() that promise so I will always be setting the state.
For me, clean the state in the unmount of the component helped.
const [state, setState] = useState({});
useEffect(() => {
myFunction();
return () => {
setState({}); // This worked for me
};
}, []);
const myFunction = () => {
setState({
name: 'Jhon',
surname: 'Doe',
})
}
Sharing the AbortController between the fetch() requests is the right approach.
When any of the Promises are aborted, Promise.all() will reject with AbortError:
function Component(props) {
const [fetched, setFetched] = React.useState(false);
React.useEffect(() => {
const ac = new AbortController();
Promise.all([
fetch('http://placekitten.com/1000/1000', {signal: ac.signal}),
fetch('http://placekitten.com/2000/2000', {signal: ac.signal})
]).then(() => setFetched(true))
.catch(ex => console.error(ex));
return () => ac.abort(); // Abort both fetches on unmount
}, []);
return fetched;
}
const main = document.querySelector('main');
ReactDOM.render(React.createElement(Component), main);
setTimeout(() => ReactDOM.unmountComponentAtNode(main), 1); // Unmount after 1ms
<script src="//cdnjs.cloudflare.com/ajax/libs/react/16.8.3/umd/react.development.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.3/umd/react-dom.development.js"></script>
<main></main>
For example, you have some component that does some asynchronous actions, then writes the result to state and displays the state content on a page:
export default function MyComponent() {
const [loading, setLoading] = useState(false);
const [someData, setSomeData] = useState({});
// ...
useEffect( () => {
(async () => {
setLoading(true);
someResponse = await doVeryLongRequest(); // it takes some time
// When request is finished:
setSomeData(someResponse.data); // (1) write data to state
setLoading(false); // (2) write some value to state
})();
}, []);
return (
<div className={loading ? "loading" : ""}>
{someData}
<Link to="SOME_LOCAL_LINK">Go away from here!</Link>
</div>
);
}
Let's say that user clicks some link when doVeryLongRequest() still executes. MyComponent is unmounted but the request is still alive and when it gets a response it tries to set state in lines (1) and (2) and tries to change the appropriate nodes in HTML. We'll get an error from subject.
We can fix it by checking whether compponent is still mounted or not. Let's create a componentMounted ref (line (3) below) and set it true. When component is unmounted we'll set it to false (line (4) below). And let's check the componentMounted variable every time we try to set state (line (5) below).
The code with fixes:
export default function MyComponent() {
const [loading, setLoading] = useState(false);
const [someData, setSomeData] = useState({});
const componentMounted = useRef(true); // (3) component is mounted
// ...
useEffect( () => {
(async () => {
setLoading(true);
someResponse = await doVeryLongRequest(); // it takes some time
// When request is finished:
if (componentMounted.current){ // (5) is component still mounted?
setSomeData(someResponse.data); // (1) write data to state
setLoading(false); // (2) write some value to state
}
return () => { // This code runs when component is unmounted
componentMounted.current = false; // (4) set it to false when we leave the page
}
})();
}, []);
return (
<div className={loading ? "loading" : ""}>
{someData}
<Link to="SOME_LOCAL_LINK">Go away from here!</Link>
</div>
);
}
Why do I keep getting this warning?
The intention of this warning is to help you prevent memory leaks in your application. If the component updates it's state after it has been unmounted from the DOM, this is an indication that there could be a memory leak, but it is an indication with a lot of false positives.
How do I know if I have a memory leak?
You have a memory leak if an object that lives longer than your component holds a reference to it, either directly or indirectly. This usually happens when you subscribe to events or changes of some kind without unsubscribing when your component unmounts from the DOM.
It typically looks like this:
useEffect(() => {
function handleChange() {
setState(store.getState())
}
// "store" lives longer than the component,
// and will hold a reference to the handleChange function.
// Preventing the component to be garbage collected after
// unmount.
store.subscribe(handleChange)
// Uncomment the line below to avoid memory leak in your component
// return () => store.unsubscribe(handleChange)
}, [])
Where store is an object that lives further up the React tree (possibly in a context provider), or in global/module scope. Another example is subscribing to events:
useEffect(() => {
function handleScroll() {
setState(window.scrollY)
}
// document is an object in global scope, and will hold a reference
// to the handleScroll function, preventing garbage collection
document.addEventListener('scroll', handleScroll)
// Uncomment the line below to avoid memory leak in your component
// return () => document.removeEventListener(handleScroll)
}, [])
Another example worth remembering is the web API setInterval, which can also cause memory leak if you forget to call clearInterval when unmounting.
But that is not what I am doing, why should I care about this warning?
React's strategy to warn whenever state updates happen after your component has unmounted creates a lot of false positives. The most common I've seen is by setting state after an asynchronous network request:
async function handleSubmit() {
setPending(true)
await post('/someapi') // component might unmount while we're waiting
setPending(false)
}
You could technically argue that this also is a memory leak, since the component isn't released immediately after it is no longer needed. If your "post" takes a long time to complete, then it will take a long time to for the memory to be released. However, this is not something you should worry about, because it will be garbage collected eventually. In these cases, you could simply ignore the warning.
But it is so annoying to see the warning, how do I remove it?
There are a lot of blogs and answers on stackoverflow suggesting to keep track of the mounted state of your component and wrap your state updates in an if-statement:
let isMountedRef = useRef(false)
useEffect(() => {
isMountedRef.current = true
return () => {
isMountedRef.current = false
}
}, [])
async function handleSubmit() {
setPending(true)
await post('/someapi')
if (!isMountedRef.current) {
setPending(false)
}
}
This is not an recommended approach! Not only does it make the code less readable and adds runtime overhead, but it might also might not work well with future features of React. It also does nothing at all about the "memory leak", the component will still live just as long as without that extra code.
The recommended way to deal with this is to either cancel the asynchronous function (with for instance the AbortController API), or to ignore it.
In fact, React dev team recognises the fact that avoiding false positives is too difficult, and has removed the warning in v18 of React.
You can try this set a state like this and check if your component mounted or not. This way you are sure that if your component is unmounted you are not trying to fetch something.
const [didMount, setDidMount] = useState(false);
useEffect(() => {
setDidMount(true);
return () => setDidMount(false);
}, [])
if(!didMount) {
return null;
}
return (
<ArtistProfileContainer>
<AlbumContainer>
{artistData ? artistData.artistAlbums.items.map(album => {
return (
<AlbumTag
image={album.images[0].url}
name={album.name}
artists={album.artists}
key={album.id}
/>
)
})
: null}
</AlbumContainer>
</ArtistProfileContainer>
)
Hope this will help you.
I had a similar issue with a scroll to top and #CalosVallejo answer solved it :) Thank you so much!!
const ScrollToTop = () => {
const [showScroll, setShowScroll] = useState();
//------------------ solution
useEffect(() => {
checkScrollTop();
return () => {
setShowScroll({}); // This worked for me
};
}, []);
//----------------- solution
const checkScrollTop = () => {
setShowScroll(true);
};
const scrollTop = () => {
window.scrollTo({ top: 0, behavior: "smooth" });
};
window.addEventListener("scroll", checkScrollTop);
return (
<React.Fragment>
<div className="back-to-top">
<h1
className="scrollTop"
onClick={scrollTop}
style={{ display: showScroll }}
>
{" "}
Back to top <span>⟶ </span>
</h1>
</div>
</React.Fragment>
);
};
I have getting same warning, This solution Worked for me ->
useEffect(() => {
const unsubscribe = fetchData(); //subscribe
return unsubscribe; //unsubscribe
}, []);
if you have more then one fetch function then
const getData = () => {
fetch1();
fetch2();
fetch3();
}
useEffect(() => {
const unsubscribe = getData(); //subscribe
return unsubscribe; //unsubscribe
}, []);
This error occurs when u perform state update on current component after navigating to other component:
for example
axios
.post(API.BASE_URI + API.LOGIN, { email: username, password: password })
.then((res) => {
if (res.status === 200) {
dispatch(login(res.data.data)); // line#5 logging user in
setSigningIn(false); // line#6 updating some state
} else {
setSigningIn(false);
ToastAndroid.show(
"Email or Password is not correct!",
ToastAndroid.LONG
);
}
})
In above case on line#5 I'm dispatching login action which in return navigates user to the dashboard and hence login screen now gets unmounted.
Now when React Native reaches as line#6 and see there is state being updated, it yells out loud that how do I do this, the login component is there no more.
Solution:
axios
.post(API.BASE_URI + API.LOGIN, { email: username, password: password })
.then((res) => {
if (res.status === 200) {
setSigningIn(false); // line#6 updating some state -- moved this line up
dispatch(login(res.data.data)); // line#5 logging user in
} else {
setSigningIn(false);
ToastAndroid.show(
"Email or Password is not correct!",
ToastAndroid.LONG
);
}
})
Just move react state update above, move line 6 up the line 5.
Now state is being updated before navigating the user away. WIN WIN
there are many answers but I thought I could demonstrate more simply how the abort works (at least how it fixed the issue for me):
useEffect(() => {
// get abortion variables
let abortController = new AbortController();
let aborted = abortController.signal.aborted; // true || false
async function fetchResults() {
let response = await fetch(`[WEBSITE LINK]`);
let data = await response.json();
aborted = abortController.signal.aborted; // before 'if' statement check again if aborted
if (aborted === false) {
// All your 'set states' inside this kind of 'if' statement
setState(data);
}
}
fetchResults();
return () => {
abortController.abort();
};
}, [])
Other Methods:
https://medium.com/wesionary-team/how-to-fix-memory-leak-issue-in-react-js-using-hook-a5ecbf9becf8
If the user navigates away, or something else causes the component to get destroyed before the async call comes back and tries to setState on it, it will cause the error. It's generally harmless if it is, indeed, a late-finish async call. There's a couple of ways to silence the error.
If you're implementing a hook like useAsync you can declare your useStates with let instead of const, and, in the destructor returned by useEffect, set the setState function(s) to a no-op function.
export function useAsync<T, F extends IUseAsyncGettor<T>>(gettor: F, ...rest: Parameters<F>): IUseAsync<T> {
let [parameters, setParameters] = useState(rest);
if (parameters !== rest && parameters.some((_, i) => parameters[i] !== rest[i]))
setParameters(rest);
const refresh: () => void = useCallback(() => {
const promise: Promise<T | void> = gettor
.apply(null, parameters)
.then(value => setTuple([value, { isLoading: false, promise, refresh, error: undefined }]))
.catch(error => setTuple([undefined, { isLoading: false, promise, refresh, error }]));
setTuple([undefined, { isLoading: true, promise, refresh, error: undefined }]);
return promise;
}, [gettor, parameters]);
useEffect(() => {
refresh();
// and for when async finishes after user navs away //////////
return () => { setTuple = setParameters = (() => undefined) }
}, [refresh]);
let [tuple, setTuple] = useState<IUseAsync<T>>([undefined, { isLoading: true, refresh, promise: Promise.resolve() }]);
return tuple;
}
That won't work well in a component, though. There, you can wrap useState in a function which tracks mounted/unmounted, and wraps the returned setState function with the if-check.
export const MyComponent = () => {
const [numPendingPromises, setNumPendingPromises] = useUnlessUnmounted(useState(0));
// ..etc.
// imported from elsewhere ////
export function useUnlessUnmounted<T>(useStateTuple: [val: T, setVal: Dispatch<SetStateAction<T>>]): [T, Dispatch<SetStateAction<T>>] {
const [val, setVal] = useStateTuple;
const [isMounted, setIsMounted] = useState(true);
useEffect(() => () => setIsMounted(false), []);
return [val, newVal => (isMounted ? setVal(newVal) : () => void 0)];
}
You could then create a useStateAsync hook to streamline a bit.
export function useStateAsync<T>(initialState: T | (() => T)): [T, Dispatch<SetStateAction<T>>] {
return useUnlessUnmounted(useState(initialState));
}
Try to add the dependencies in useEffect:
useEffect(() => {
fetchData()
return () => { props.spotifyAPI.cancelRequest() }
}, [fetchData, props.spotifyAPI])
Usually this problem occurs when you showing the component conditionally, for example:
showModal && <Modal onClose={toggleModal}/>
You can try to do some little tricks in the Modal onClose function, like
setTimeout(onClose, 0)
This works for me :')
const [state, setState] = useState({});
useEffect( async ()=>{
let data= await props.data; // data from API too
setState(users);
},[props.data]);
I had this problem in React Native iOS and fixed it by moving my setState call into a catch. See below:
Bad code (caused the error):
const signupHandler = async (email, password) => {
setLoading(true)
try {
const token = await createUser(email, password)
authContext.authenticate(token)
} catch (error) {
Alert.alert('Error', 'Could not create user.')
}
setLoading(false) // this line was OUTSIDE the catch call and triggered an error!
}
Good code (no error):
const signupHandler = async (email, password) => {
setLoading(true)
try {
const token = await createUser(email, password)
authContext.authenticate(token)
} catch (error) {
Alert.alert('Error', 'Could not create user.')
setLoading(false) // moving this line INTO the catch call resolved the error!
}
}
Similar problem with my app, I use a useEffect to fetch some data, and then update a state with that:
useEffect(() => {
const fetchUser = async() => {
const {
data: {
queryUser
},
} = await authFetch.get(`/auth/getUser?userId=${createdBy}`);
setBlogUser(queryUser);
};
fetchUser();
return () => {
setBlogUser(null);
};
}, [_id]);
This improves upon Carlos Vallejo's answer.
useEffect(() => {
let abortController = new AbortController();
// your async action is here
return () => {
abortController.abort();
}
}, []);
in the above code, I've used AbortController to unsubscribe the effect. When the a sync action is completed, then I abort the controller and unsubscribe the effect.
it work for me ....
The easy way
let fetchingFunction= async()=>{
// fetching
}
React.useEffect(() => {
fetchingFunction();
return () => {
fetchingFunction= null
}
}, [])
options={{
filterType: "checkbox"
,
textLabels: {
body: {
noMatch: isLoading ?
:
'Sorry, there is no matching data to display',
},
},
}}
I am using gitbeaker to get a project from gitlab API, after fetching the project, I used useState to save the project object, now I want to fetch another API whose URL is in that object, but whenever I try to access that URL, an error appears "Cannot read property 'issues' of undefined".
Here's my code:
const [project, setProject] = useState<any>({});
const api = new Gitlab({
host: "https://example.com",
token: "my token",
});
useEffect(() => {
(async () => {
const projectsPromises = await api.Projects.all().then((allprojects) => {
return allprojects;
});
Promise.all(projectsPromises).then((data) => {
setProject(data.find((element) => element.id === 338));
});
})();
return () => {};
}, []);
console.log(project);
console.log(project._links.issues);
fetch(project._links.issues).then((res) => console.log(res));
console.log(project); gives me {} and after some time it prints the object, that's why when I try to use project._links.issues it is undefined as I think it isn't resolved yet but I don't know how to make it work.
I solved it by fetching the data in the useEffect hook and saving the response of the api in the state so that I can access it later in my code, like that
const [issues, setIssues] = useState<any>([]);
Promise.all(projectsPromises).then((data) => {
const celoProject: any = data.find((element) => element.id === 338);
setProject(celoProject);
const projectIssues = fetch(celoProject._links.issues)
.then((res) => res.json())
.then((allIssues) => {
setIssues(allIssues);
});
});
If someone has a better way or an explanation why I couldn't access it outside the useEffect, please tell me.
Anything inside the useEffect hook will only execute when the page first loads (because you provided an empty array as the second argument). Anything outside of it will execute on every render (every time props or state changes). That is why it logs {} the first time because the effect is asynchronous and hasn't completed before the component is rendered.
You should run the second fetch in the useEffect hook after the first API request completes. Need more information to determine what exactly is happening beyond this.
const [project, setProject] = useState<any>({});
const api = new Gitlab({
host: "https://example.com",
token: "my token",
});
useEffect(() => {
(async () => {
const projectsPromises = await api.Projects.all().then((allprojects) => {
return allprojects;
});
Promise.all(projectsPromises).then((data) => {
const projectResponse = data.find((element) => element.id === 338)
setProject(projectResponse)
fetch(projectResponse._links.issues).then((res) => {
console.log(res)
// Do something with this response
});
});
})();
return () => {};
}, []);
console.log(project);
console.log(project._links.issues);
I'm trying to get the value of googleToken inside a <div> in the return of my React Component. The value is already updated, but it's the initial state here in the return, therefore, it always shows null
const Layout = props => {
let googleToken = null;
useEffect( () => {
fetchGoogleToken();
}, [])
const fetchGoogleToken = async () => {
await api
.get("/google_token")
.then((response) => {
console.log('google_token: ' + response.data.google_token);
googleToken = response.data.google_token;
console.log('google_token updated: ' + googleToken);
})
.catch((error) => console.log(error));
};
const getGoogleToken = (res) => {
console.log(res);
setGoogleToken(res.accessToken);
saveGoogleTokenInDB();
};
const saveGoogleTokenInDB = async () => {
await api
.post("/fit-auth", {google_token : googleToken})
.then((response) => {
console.log(response);
})
.catch((error) => console.log(error));
};
return (
<div className={classes.googleButton} style={{display: googleToken === null ? 'block' : 'none'}}>
<h3>{googleToken}</h3>
<div/>
}
Any ideas on why I can't get the updated value?
It is right to use useEffect hook for fetching. But the result must be kept into state. And when you ask react to update state, you can not watch changes on the next line of code using console.log because setState is async function and it will be executed later on.
// this will never work as you might be expected:
setState(newState)
console.log(state)
To catch state updates always use useEffect hook as in example below:
useEffect(() => {
console.log(state)
}, [state])
Also, avoid using inline styles for showing / hiding your components. Check the official conditional rendering recommendations.
The final code is going to look like this:
const Layout = props => {
const [googleToken, setGoogleToken] = useState(null)
useEffect( () => {
fetchGoogleToken();
}, [])
// you can watch how state changes only using useEffect:
useEffect(() => {
console.log('google_token updated: ' + googleToken)
}, [googleToken])
const fetchGoogleToken = async () => {
await api
.get("/google_token")
.then((response) => {
console.log('google_token: ' + response.data.google_token);
setGoogleToken(response.data.google_token);
})
.catch((error) => console.log(error));
};
// conditional rendering:
if (!googleToken) return <span>Fetching token...</span>
return (
<div className={classes.googleButton}>
<h3>{googleToken}</h3>
<div/>
)
}
Hope you will find this helpful.
The issue is that when the value of googleToken is updated the component is not notified about this. Since the component is not notified about the change it still believes that the value is still the initial value and it does need to change anything in DOM.
To solve this issue try using states or just force a rerender once the function is executed.
I'm not quite understand how useEffect cleanup function work. Because whatever I do I always get warning:
Warning: Can't perform a React state update on an unmounted component. This is a no-op, but it indicates a memory leak in your application. To fix, cancel all subscriptions and asynchronous tasks in a useEffect cleanup function.
Here is my code:
useEffect(() => {
setLoading(true)
// Get position list
const getPositionList = db.collection('lists').doc('positions').get()
.then( res => {
let data = JSON.stringify(res.data())
data = JSON.parse(data)
setPositionsList(data.list)
setLoading(false)
})
return () => getPositionList
}, [])
useEffect expects as a return value an unsubscribe/cleanup function, or a null. Your .get() is NOT a subscription, so there's nothing to clean up
BUT useEffect is NOT asynchronous, and the .get() definitively returns a promise that needs a delay, even with the .then(). Your dependency array is empty, so useEffect is only called once - but I suspect your component unmounted before the .get() ever returned.
Your code will need to be closer to:
useEffect(() => {
setLoading(true)
(async () => {
// Get position list
await db.collection('lists').doc('positions').get()
.then( res => {
let data = JSON.stringify(res.data())
data = JSON.parse(data)
setPositionsList(data.list)
setLoading(false)
});
)();
return null
}, [])
the ( async () => {})() creates an anonymous asynchronous function, then executes it. You do want to try to structure your system such that the enclosing component does not unmount before loading is set to false - we don't see that here, so we have to assume you do that part right.
The important take-aways:
useEffect is NOT asynchronous
.get() IS asynchronous
( async () => {}) creates an anonymous async function, and ( async () => {})() creates a self-executing anonymous asynchronous function
useEffect(() => {
setLoading(true)
// below firebase api return promise. hence no need to unsubscribe.
db.collection('lists').doc('positions').get()
.then( res => {
let data = JSON.stringify(res.data())
data = JSON.parse(data)
setPositionsList(data.list)
setLoading(false)
})
return () => {
// any clean up code, unsubscription goes here. unmounting phase
}
}, [])
According #Dennis Vash answer I figure out, that before setting state I have to check is component mounted or not, so I add variable in useEffect and before set state I check I add if statement:
useEffect(() => {
setLoading(true)
let mounted = false // <- add variable
// Get position list
db.collection('lists').doc('positions').get()
.then( res => {
let data = JSON.stringify(res.data())
data = JSON.parse(data)
if(!mounted){ // <- check is it false
setPositionsList(data.list)
setLoading(false)
}
})
return () => {
mounted = true // <- change to true
}
}, [])