i have a problem with an hooks.
When i make
export default function Checkout() {
const { readRemoteFile } = usePapaParse();
const [parsedCsvData, setParsedCsvData] = useState([]);
const handleReadRemoteFile = file => {
readRemoteFile(file, {
complete: (results) => {
setParsedCsvData(results.data);
},
});
};
handleReadRemoteFile(CSVsource);
}
I have an infinite loop but when i make
export default function Checkout() {
const { readRemoteFile } = usePapaParse();
const [parsedCsvData, setParsedCsvData] = useState([]);
const handleReadRemoteFile = file => {
readRemoteFile(file, {
complete: (results) => {
console.log(results.data);
},
});
};
handleReadRemoteFile(CSVsource);
}
I have'nt the problem.
Have you an idea ?
Thank's Yann.
While the component code you posted is still incomplete (CSVsource is undefined, there's no return), I think the problem is visible now:
You're running handleReadRemoteFile(CSVsource) on every render (because you're calling it directly). When the file is read, you are setting parsedCsvData, which (because state updates and prop updates trigger a rerender) renders the component again, triggering handleReadRemoteFile once again...
So what's the solution?
Data fetching is a classical example of using the useEffect hook. The following code should do what you want
const { readRemoteFile } = usePapaParse();
const [parsedCsvData, setParsedCsvData] = useState([]);
useEffect(()=>{
readRemoteFile(CSVSource, {
complete: results => setParsedCsvData(results.data);
});
}, [CSVsource]); // rerun this whenever CSVSource changes.
Please read up on the useEffect hook in the React docs.
Note: there's one problem with the code I posted above. When the component is unmounted while the CSV is still loading, you will get an error "state update on unmounted component" as soon as the loading finished. To mitigate this, use the return function of useEffect in combination with a local variable.
So the final code looks like this:
useEffect(()=>{
let stillMounted = true;
readRemoteFile(CSVSource, {
complete: results => {
if(!stillMounted) return; // prevent update on unmounted component
setParsedCsvData(results.data);
}
});
return ()=>stillMounted = false; // this function is ran before the effect is ran again and on unmount
}, [CSVsource]);
Related
I have a component in my react native app that loads sessions related to a particular individual. In the useEffect() of that component I both load the sessions when the component comes into focus, and unload those sessions within the cleanup.
export const ClientScreen = (props) => {
const isFocused = useIsFocused();
const client = useSelector((state) => selectActiveClient(state));
useEffect(() => {
if (isFocused) {
const loadSessions = async () => {
if (client?.id) {
dispatch(await loadClientSessions(client?.id));
}
return () => dispatch(unloadSessions()); // Cleaning up here...
};
loadSessions(props);
}
}, [isFocused, client?.id]);
const updatedProps = {
...props,
client,
};
return <ClientBottomTabNavigator {...updatedProps} />;
};
Generally the component is working as expected. However, I do notice that if I load the component with one client, then navigate away, and then come back to the component by loading a new client, that for a brief moment the sessions pertaining to the previous client show before being replaced the sessions relevant to the new client.
My question is, shouldn't the unloadVisits() that runs on cleanup -- which sets sessions to an empty array -- prevent this? Or is this some kind of react behavior that's holding onto the previous state of the component? How can I ensure this behavior doesn't occur?
Cleanup function should appear before the closing-brace of the useEffect hook
useEffect(() => {
if (isFocused) {
const loadSessions = async () => {
if (client?.id) {
dispatch(await loadClientSessions(client?.id));
}
};
loadSessions(props);
}
return () => dispatch(unloadSessions()); // Cleaning up here... // <--- here
}, [isFocused, client?.id]);
as commented, your loadSessions returns a cleanup function, but you don't do anything with it. And the effect where you call loadSessions(props) does not return anything, that's why it does not clean up.
Edit:
I made a mistake, loadSessions returns a Promise of a cleanup function. And it is impossible to "unwrap" this Promise and get to the cleanup function itself in a way that you can return it in your effect. You have to move the cleaup function out of the async function loadSessions.
But you don't need async/await for everything:
useEffect(() => {
if (isFocused && client?.id) {
loadClientSessions(client.id).then(dispatch);
return () => dispatch(unloadSessions());
}
}, [isFocused, client?.id]);
I am using React with typescript and I want to convert my class component to a functional component, but my class component has two different componentDidMount and comonentDidUpdate behaviors:
componentDidMount() {
this.props.turnResetOff();
}
componentDidUpdate() {
if (this.props.resetForm) {
this.resetChangeForm();
this.props.turnResetOff();
}
}
I just want my form to reset every time it loads except the first time, because I have a menu drop-down that allows clearing the form but I want the data to not reset on mount.
I tried using this: componentDidMount equivalent on a React function/Hooks component?
const turnResetOff = props.turnResetOff;// a function
const resetForm = props.resetForm;
const setPersonId = props.setPersonId;// a function
useEffect(() => {
turnResetOff();
}, [turnResetOff]);
useEffect(() => {
const resetChangeForm = () => {/*definition*/};
if (resetForm) {
resetChangeForm();
turnResetOff();
}
}, [resetForm, turnResetOff, setPersonId]);
However, this causes an infinite re-render. Even if I useCallback for turnResetOff:
turnResetOff={useCallback(() => {
if (shouldReset) {
setShouldReset(false);
}
}, [shouldReset])}
I also tried using useRef to count the number of times this has been rendered, with the same result (infinite rerender - this is a simplified version even).
const [shouldReset, setShouldReset] = useState<boolean>(false);
const mountedTrackerRef = useRef(false);
useEffect(() => {
if (mountedTrackerRef.current === false) {
console.log("mounted now!");
mountedTrackerRef.current = true;
// props.turnResetOff();
setShouldReset(false);
} else {
console.log("mounted already... updating");
// if (props.resetForm) {
if (shouldReset) {
// resetChangeForm();
// props.turnResetOff();
setShouldReset(false);
}
}
}, [mountedTrackerRef, shouldReset]);
When you call useEffect() you can return a clean-up function. That cleanup function gets called when the component is unmounted. So, perhaps what you want to do is this: when you are called with turnResetOff then call it, and return a function that calls turnResetOff. The return function will be called when the component unmounts, so next time the component mounts it won't reset.
Something to along these lines:
useEffect(
() => {
turnResetOff()
return () => {setShouldReset(false)}
}
,[turnResetOff, setShouldReset])
Using the logic you have in the class component, the fellowing should give you identical behavior in a functional component
const turnResetOff = props.turnResetOff;// a function
const resetForm = props.resetForm;
const setPersonId = props.setPersonId;// a function
// useEffect with an empty dependency array is identical to ComponentDidMount event
useEffect(() => {
turnResetOff();
}, []);
// Just need resetForm as dependency since only resetForm was checked in the componentDidUpdate
useEffect(() => {
const resetChangeForm = () => {/*definition*/};
if (resetForm) {
resetChangeForm();
turnResetOff();
}
}, [resetForm]);
This is a React style question.
TL;DR Take the set function from React's useState. If that function "changed" every render, what's the best way to use it in a useEffect, with the Effect running only one time?
Explanation We have a useEffect that needs to run once (it fetches Firebase data) and then set that data in application state.
Here is a simplified example. We're using little-state-machine, and updateProfileData is an action to update the "profile" section of our JSON state.
const MyComponent = () => {
const { actions, state } = useStateMachine({updateProfileData, updateLoginData});
useEffect(() => {
const get_data_async = () => {
const response = await get_firebase_data();
actions.updateProfileData( {user: response.user} );
};
get_data_async();
}, []);
return (
<p>Hello, world!</p>
);
}
However, ESLint doesn't like this:
React Hook useEffect has a missing dependency: 'actions'. Either include it or remove the dependency array
Which makes sense. The issue is this: actions changes every render -- and updating state causes a rerender. An infinite loop.
Dereferencing updateProfileData doesn't work either.
Is it good practice to use something like this: a single-run useEffect?
Concept code that may / may not work:
const useSingleEffect = (fxn, dependencies) => {
const [ hasRun, setHasRun ] = useState(false);
useEffect(() => {
if(!hasRun) {
fxn();
setHasRun(true);
}
}, [...dependencies, hasRun]);
};
// then, in a component:
const MyComponent = () => {
const { actions, state } = useStateMachine({updateProfileData, updateLoginData});
useSingleEffect(async () => {
const response = await get_firebase_data();
actions.updateProfileData( {user: response.user} );
}, [actions]);
return (
<p>Hello, world!</p>
);
}
But at that point, why even care about the dependency array? The initial code shown works and makes sense (closures guarantee the correct variables / functions), ESLint just recommends not to do it.
It's like if the second return value of React useState changed every render:
const [ foo, setFoo ] = useState(null);
// ^ this one
If that changed every render, how do we run an Effect with it once?
Ignore the eslint rule for line
If you truly want the effect to run only once exactly when the component mounts then you are correct to use an empty dependency array. You can disable the eslint rule for that line to ignore it.
useEffect(() => {
const get_data_async = () => {
const response = await get_firebase_data();
actions.updateProfileData( {user: response.user} );
};
get_data_async();
// NOTE: Run effect once on component mount, please
// recheck dependencies if effect is updated.
// eslint-disable-next-line react-hooks/exhaustive-deps
}, []);
Note: If you later update the effect and it needs to run after other dependencies then this disabled comment can potentially mask future bugs, so I suggest leaving a rather overt comment as for the reason to override the established linting rule.
Custom hook logic
Alternatively you can use a react ref to signify the initial render. This is preferable to using some state to hold the value as updating it would trigger unnecessary render.
const MyComponent = () => {
const { actions, state } = useStateMachine({updateProfileData, updateLoginData});
const initialRenderRef = useRef(true);
useEffect(() => {
const get_data_async = () => {
const response = await get_firebase_data();
actions.updateProfileData( {user: response.user} );
};
if (initialRenderRef.current) {
initialRenderRef.current = false;
get_data_async();
}
}, [actions]); // <-- and any other dependencies the linter complains about
return (
<p>Hello, world!</p>
);
}
And yes, absolutely you can factor this "single-run logic" into a custom hook if it is a pattern you find used over and over in your codebase.
I am using Effect hook to fetch the datas from server and these data are passed to the react table there i have used the same api call to load the next set of datas from server.
When the application gets loaded i am getting an warning like below
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.
Effect Hook:
useEffect(() => {
setPageLoading(true);
props
.dispatch(fetchCourses())
.then(() => {
setPageLoading(false);
})
.catch((error: string) => {
toast.error(error);
setPageLoading(false);
});
}, []);
React Table Page:
<ReactTable
className="-striped -highlight"
columns={columns}
data={coursesData}
defaultPage={currentPage}
defaultPageSize={courses.perPage}
loading={isLoading}
manual={true}
onFetchData={setFilter}
/>
Set Filter function:
const setFilter = (pagination: any) => {
props.dispatch(updateCoursePageSize(pagination.pageSize));
props.dispatch(updateCourseCurrentPage(pagination.page + 1));
setCurrentPage(pagination.page);
setPerPage(pagination.pageSize);
setLoading(true);
props.dispatch(fetchCourses()).then(() => {
setLoading(false);
});
};
Does anyone know how to clean up the hook in react
Update (June 2022):
React 18 has removed this warning message, and the workarounds to get rid of it may no longer be necessary. Part of the reason they removed it is that it has always been a bit misleading. It says you have a memory leak, but often times you don't.
The code in the question -- and indeed most code that causes this warning -- runs for a finite amount of time past the unmounting of the component, then sets state, then is done running. Since it's done running, javascript can free up variables in its closure, and thus there is usually no leak.
The case where you will have a memory leak is if you are setting up a persistent subscription which continues indefinitely. For example, maybe you set up a websocket and listen to messages, but you never tear down that websocket. These cases do need to be fixed (by supplying a cleanup function to the useEffect) but they are uncommon.
The other reason react 18 has removed the warning is that they are working on the ability for components to preserve their state after being unmounted. Once that feature is in react, setting state after unmount will be a perfectly valid thing to do.
Original answer (September 2019):
With useEffect you can return a function that will be run on cleanup. So in your case, you'll want something like this:
useEffect(() => {
let unmounted = false;
setPageLoading(true);
props
.dispatch(fetchCourses())
.then(() => {
if (!unmounted) {
setPageLoading(false);
}
})
.catch((error: string) => {
if (!unmounted) {
toast.error(error);
setPageLoading(false);
}
});
return () => { unmounted = true };
}, []);
EDIT: if you need to have a call that's kicked off outside of useEffect, then it will still need to check an unmounted variable to tell whether it should skip the call to setState. That unmounted variable will be set by a useEffect, but now you need to go through some hurdles to make the variable accessible outside of the effect.
const Example = (props) => {
const unmounted = useRef(false);
useEffect(() => {
return () => { unmounted.current = true }
}, []);
const setFilter = () => {
// ...
props.dispatch(fetchCourses()).then(() => {
if (!unmounted.current) {
setLoading(false);
}
})
}
// ...
return (
<ReactTable onFetchData={setFilter} /* other props omitted */ />
);
}
you can create a custom hook for that like that :
import * as React from 'react';
export default function useStateWhenMounted<T>(initialValue: T) {
const [state, setState] = React.useState(initialValue);
const isMounted = React.useRef(true);
React.useEffect(() => {
return () => {
isMounted.current = false;
};
}, []);
const setNewState = React.useCallback((value) => {
if (isMounted.current) {
setState(value);
}
}, []);
return [state, setNewState];
}
Memory leak happens, when a thing that is unnecessary and is supposed to be cleared from memory is kept because some other thing is still holding it. In React Component case, the async call made in component may hold the references of setState or other references and will hold them until the call completes.
The warning you see is from React saying that something is still holding and setting state of a component instance that was removed from tree long back when component unmounted. Now using a flag to not set the state only removes the warning but not the memory leak, even using Abort controller does the same. To escape this situation you can use state management tools that helps dispatching an action which will do processing out side of component without holding any memory references of the component, for example redux. If you are not using such tools then you should find a way to clear the callbacks you pass to the async call (then, catch, finally blocks) when component unmounts. In the below snippet I am doing the same detaching the references to the methods passed to async call to avoid memory leaks.
Event Emitter here is an Observer, you can create one or use some package.
const PromiseObserver = new EventEmitter();
class AsyncAbort {
constructor() {
this.id = `async_${getRandomString(10)}`;
this.asyncFun = null;
this.asyncFunParams = [];
this.thenBlock = null;
this.catchBlock = null;
this.finallyBlock = null;
}
addCall(asyncFun, params) {
this.asyncFun = asyncFun;
this.asyncFunParams = params;
return this;
}
addThen(callback) {
this.thenBlock = callback;
return this;
}
addCatch(callback) {
this.catchBlock = callback;
return this;
}
addFinally(callback) {
this.finallyBlock = callback;
return this;
}
call() {
const callback = ({ type, value }) => {
switch (type) {
case "then":
if (this.thenBlock) this.thenBlock(value);
break;
case "catch":
if (this.catchBlock) this.catchBlock(value);
break;
case "finally":
if (this.finallyBlock) this.finallyBlock(value);
break;
default:
}
};
PromiseObserver.addListener(this.id, callback);
const cancel = () => {
PromiseObserver.removeAllListeners(this.id);
};
this.asyncFun(...this.asyncFunParams)
.then((resp) => {
PromiseObserver.emit(this.id, { type: "then", value: resp });
})
.catch((error) => {
PromiseObserver.emit(this.id, { type: "catch", value: error });
})
.finally(() => {
PromiseObserver.emit(this.id, { type: "finally" });
PromiseObserver.removeAllListeners(this.id);
});
return cancel;
}
}
in the useEffect hook you can do
React.useEffect(() => {
const abort = new AsyncAbort()
.addCall(simulateSlowNetworkRequest, [])
.addThen((resp) => {
setText("done!");
})
.addCatch((error) => {
console.log(error);
})
.call();
return () => {
abort();
};
}, [setText]);
I forked someones code from here to use above logic, you can check it in action in the below link
link
The other answers work of course, I just wanted to share a solution I came up with.
I built this hook that works just like React's useState, but will only setState if the component is mounted. I find it more elegant because you don't have to mess arround with an isMounted variable in your component !
Installation :
npm install use-state-if-mounted
Usage :
const [count, setCount] = useStateIfMounted(0);
You can find more advanced documentation on the npm page of the hook.
I'm having a little trouble figuring out how to change my authentication handling component when refactoring from a React class to React hooks.
Here's the relavant code in my class:
state = {
user: null
}
componentDidMount() {
authGetUser(user => {
if (user !== this.state.user) {
this.setState({user})
}
})
}
componentWillUnmount() {
authUnsubscribe()
}
handleAuthClick = () => {
if (this.state.user) {
authSignOut()
} else {
authSignIn()
}
}
And here it is with hooks:
const [user, setUser] = useState<firebase.User | null>(null)
useEffect(() => {
return authUnsubscribe() // runs on mount and unmount only
}, [])
useEffect(() => {
authGetUser(usr => setUser(usr))
}, [])
const handleAuthClick = () => {
if (user) {
authSignOut()
} else {
authSignIn()
}
}
Also, here are my other relevant methods:
const authGetUser = (callback: (user: firebase.User | null) => void) => {
initFirebase()
authUnsubscribe()
userUnsubscribe = firebaseAuth.onAuthStateChanged(callback)
}
export const authUnsubscribe = () => {
if (userUnsubscribe) {
userUnsubscribe()
}
}
const authSignIn = () => {
googleAuth.signIn().then((googleUser: any) => {
var credential = firebase.auth.GoogleAuthProvider.credential(googleUser.getAuthResponse().id_token)
firebaseAuth.signInAndRetrieveDataWithCredential(credential)
})
}
const authSignOut = () => {
googleAuth
.signOut()
.then(firebaseAuth.signOut())
}
Both examples work. However, when I log out and log in with the hooks version, I get an error message in console saying
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 the componentWillUnmount method.
which suggests that the cleanup is not done properly.
Yes, I know I could just continue using the version with the class which works. But I want to understand React hooks better by solving this.
Any ideas?
Wouldn't this works for you? You could use a single useEffect().
React Hooks API DOCs
useEffect(
() => {
const subscription = props.source.subscribe();
return () => {
// Clean up the subscription
setUser(null); // <--- TRY DOING SOMETHING LIKE THIS
subscription.unsubscribe();
};
},
[],
);
The clean-up function runs before the component is removed from the UI
to prevent memory leaks. Additionally, if a component renders multiple
times (as they typically do), the previous effect is cleaned up before
executing the next effect. In our example, this means a new
subscription is created on every update. To avoid firing an effect on
every update, refer to the next section.
If you want to run an effect and clean it up only once (on mount and
unmount), you can pass an empty array ([]) as a second argument. This
tells React that your effect doesn’t depend on any values from props
or state, so it never needs to re-run. This isn’t handled as a special
case — it follows directly from how the dependencies array always
works.
Generally, this happens when we have asynchronous requests and the component is unmounted before, occurring memory leak. Obviously, that this not occur in class-based components because we have componentDidMount() and componentWillUnmount() hooks, so it's more confident than useEffect() that we have manipulated the state, so I think that you need to identify the reason for the application unmount and there is the solution.
You should use one useEffect() instead two like this:
useEffect(() => {
authGetUser(usr => setUser(usr))
return authUnsubscribe() // runs on mount and unmount only
}, [])