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',
},
},
}}
Below is my custom hook, I'm trying to handle everything from the hook. I have seen similar questions but none seems to work for my case and I have been made to believe there's a solution for this approach, jus can't figure it out.
const useResource = (baseUrl) => {
const [resources, setResources] = useState([]);
const create = async (resource) => {
const response = await axios.post(baseUrl, resource)
setResources(resources.concat(response.data));
console.log(resources)
return response.data
}
const get = async () => {
const response = await axios.get(baseUrl);
setResources(response.data)
return response.data
}
const service = {
create,
get
}
return [
resources, service
]
}
Here is my approach to use the custom hook, but request keeps looping nonstop, please how do I stop it running after every render?
const App = () => {
const content = useField('text');
const name = useField('text');
const number = useField('text');
const [notes, noteService] = useResource('http://localhost:3005/notes');
const [persons, personService] = useResource('http://localhost:3005/persons');
useEffect(() => {
noteService.get();
}, [noteService])
useEffect(() => {
personService.get();
}, [personService])
const handleNoteSubmit = (event) => {
event.preventDefault();
noteService.create({ content: content.value });
}
const handlePersonSubmit = (event) => {
event.preventDefault();
personService.create({ name: name.value, number: number.value});
}
Edit: I just had to disable ESLint for the dependency line, because I just need it to run once after every render. Works well!
useEffect(() => {
noteService.get();
// eslint-disable-next-line react-hooks/exhaustive-deps
}, [])
useEffect(() => {
personService.get();
// eslint-disable-next-line react-hooks/exhaustive-deps
}, [])
As correctly pointed out in comments, each time the component renders and calls your useResource hook, a new service object is created. If this service object is used as a dependency for any other hooks this will trigger their callbacks.
The solution is to memoize the service object so it's being provided as a stable reference. This can be accomplished via the useMemo hook. Because service will be memoized, the create callback will also be memoized and contain stale resources state. To address this update create to use a functional state update when appending new response data to the existing state.
Example:
import { useEffect, useMemo, useState } from 'react';
const useResource = (baseUrl) => {
const [resources, setResources] = useState([]);
const create = async (resource) => {
const response = await axios.post(baseUrl, resource);
// Functional update to update from previous state
setResources(resources => resources.concat(response.data));
return response.data;
}
const get = async () => {
const response = await axios.get(baseUrl);
setResources(response.data);
return response.data;
}
const service = useMemo(() => ({
create,
get
}), []);
return [resources, service];
};
I'm trying to debounce() an Observable with pipe() and chaining .subscribe() but for some reason the function in the subscribe is still being called over a dozen times in one go.
What I'm trying to do is pipe the withChangesForTables and debounce the sync call because I want it to be called only when a whole batch of changes have been made. So I created a provider for the sync and wrapped it around my RootNavigator
withChangesForTables on WatermelonDB source code
const SyncContext = createContext();
function useSync() {
return useContext(SyncContext);
}
function SyncProvider({children}) {
const [isSyncing, setIsSyncing] = useState(false);
const [hasUnsynced, setHasUnsynced] = useState(false);
async function checkUnsyncedChanges() {
const hasChanges = await hasUnsyncedChanges({
database
});
setHasUnsynced(hasChanges);
}
async function sync() {
await checkUnsyncedChanges();
if (!isSyncing && hasUnsynced) {
setIsSyncing(true);
await synchronizeWithServer();
setIsSyncing(false);
}
}
database.withChangesForTables([
'table_name',
'table_name2'
]).pipe(
skip(1),
// ignore records simply becoming `synced`
filter(changes => !changes.every(change => change.record.syncStatus === 'synced')),
// debounce to avoid syncing in the middle of related actions - I put 100000 to test only
debounceTime(100000),
).subscribe({
//calls API endpoint to sync local DB with server
next: () => sync(),
error: e => console.log(e)
});
const value = {
isSyncing,
hasUnsynced,
checkUnsyncedChanges,
sync
};
return (
<SyncContext.Provider value={value}>
{children}
</SyncContext.Provider>
);
}
I had to move withChangesForTables into a useEffect and retrun it in order to unsubcribe which seems to have resolved the issue. The code now looks something like this:
useEffect(() => {
return database.withChangesForTables([
'table_name',
'table_name2'
]).pipe(
skip(1),
filter(changes => !changes.every(change => change.record.syncStatus === 'synced')),
debounceTime(500),
).subscribe({
next: () => sync(),
error: e => console.log(e)
});
}, [])
I'm essentially brand new to React, so please bear with me if there are any strange or obvious mistakes that I am missing.
I am looking to create a small little project with the National Hockey League statistics API and unfortunately have run into an issue pretty early on.
Essentially, what this code is trying to do right now is to fetch all of the current team ID's through https://statsapi.web.nhl.com/api/v1/teams, and then loop through each team's response and use it's unique ID to store every player ID currently playing in the league https://statsapi.web.nhl.com/api/v1/teams/ID/roster.
The API requests seem to be working just fine, however I'm running into an issue where the check for loading seems to be functioning improperly. If I say, for example
{loading ? <p>Loading...</p> : <p>{playerList[0].jerseyNumber}</p>}
I am given a "Cannot read properties of undefined" error message.
Is the way I attempted to signify loading incorrect? Is there a better way to be certain that the API requests are 100% finished before accessing the data?
Here is my code:
function App() {
const [playerList, setPlayerList] = useState([]);
const [loading, setLoading] = useState(true);
useEffect (() => {
fetch("https://statsapi.web.nhl.com/api/v1/teams")
.then((teamsResponse) => teamsResponse.json())
.then((teamsData) => {
const teams = teamsData.teams;
teams.forEach((team) => {
fetch("https://statsapi.web.nhl.com/api/v1/teams/" + team.id + "/roster")
.then((teamResponse) => teamResponse.json())
.then((teamData) => {
const roster = teamData.roster
roster.forEach((player) => {
setPlayerList((oldList) => [...oldList, player]);
});
});
});
});
setLoading(false);
}, []);
return (
<div>
{loading ? <p>Loading...</p> : playerList && <p>{playerList[0].jerseyNumber}</p>}
</div>
);
}
You're calling setLoading(false) outside of the fetch call. That is going to invoke the fetch and call setLoading(false) without waiting for the promise to resolve.
If you want the loading indicator to be set to false only after all of the roster fetch calls then you'll need to use Promise.all with a then. where you set the loading indicator to false, such as:
const teams = teamsData.teams;
const rosterRequests = teams.map(team => {
fetch("https://statsapi.web.nhl.com/api/v1/teams/" + team.id + "/roster")
.then(teamResponse => teamResponse.json())
.then(teamData => {
// Update roster state
});
// This will be executed once all the team roster requests have completed
Promise.all(rosterRequests).then(() => setLoading(false));
You can read more about Promise.all here.
setLoading should be set to false when all promises are settled since there are nested requests, I have updated and tested the solution
Updated code
useEffect(() => {
fetch("https://statsapi.web.nhl.com/api/v1/teams")
.then((teamsResponse) => teamsResponse.json())
.then((teamsData) => {
const teams = teamsData.teams;
let arr = [];
const allRosterData = teams.map(async (team) => {
const rosterData = await fetch(
"https://statsapi.web.nhl.com/api/v1/teams/" + team.id + "/roster"
)
.then((teamResponse) => teamResponse.json())
.then((teamData) => {
const dt = [];
const roster = teamData.roster;
roster.forEach((player) => {
dt.push(player);
});
return dt;
});
arr = [...arr, ...rosterData];
return rosterData;
});
Promise.all(allRosterData)
.then(() => {
//Change state here when all promises are settled
setPlayerList(arr);
setLoading(false);
})
.catch((err) => {
console.error(err);
});
});
}, []);
You are setting loading to false before the data is loaded. Try putting setLoading(false); into
.then((teamData) => {
const roster = teamData.roster
roster.forEach((player) => {
setPlayerList((oldList) => [...oldList, player]);
});
setLoading(false); <---
});