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 trying to build a cryptocurrency application. But I am having trouble getting populated state values that are passed into the useEffect as parameters to a debouncing/polling function.
The issue is that the debouncing works well, as in it detects the value and calls the api after the 500ms that I specified in debounce. However, the polling portion seems to not have the state values of of transactionType, fromCurrencyAmount, and pair. It seems like after I debounce the input, after 6 seconds the polling will do its thing but the values passed in the params are undefined. Is there anyway I can solve this?
Here is the method that serves two purposes. It has an api to be polled from every 6 seconds, as well as getting debounced input if the user enters an amount inside the input.
function handleInitPoll(baseAndQuote, side, value) {
getSwapPrice(baseAndQuote, side, value || 0)
.then((res) => {
if (!res.price) {
setIsLoading(true);
} else if (res.error) {
setErrorMessage(res.error);
} else if (res.price) {
setIsLoading(false);
setSwapPriceInfo(res);
}
});
}
And here is the useEffect:
useEffect(() => {
handleInitPoll(pair, transactionType, fromCurrencyAmount);
const timer = setInterval(handleInitPoll, 6000, pair, transactionType, fromCurrencyAmount);
return () => {
clearInterval(timer);
};
}
setSelectedCurrencyState({ ...selectedCurrencyState, selectedFromCurrency: 'USDT', selectedToCurrency: 'XLM' });
}, [pair, transactionType, fromCurrencyAmount]);
And here is the debounce declaration:
const debounceOnChange = useCallback(debounce(handleInitPoll, 500, pair, transactionType, fromCurrencyAmount), []);
And here is where the debouncing is being done, which is inside an onChange handler:
const handleAssetAmount = (e) => {
const { value } = e.target;
const formattedAmount = handleAssetAmountFormat(value);
setFromCurrencyAmount(formattedAmount);
validateInputAmount(formattedAmount);
debounceOnChange(pair, transactionType, formattedAmount);
};
Issue
The issue here is that you've closed over stale values in the interval callback.
Solution
One solution is to cache these state values in a React ref such that the current value can be accessed in the polling function.
Example:
const pairRef = React.useRef(pair);
const transactionTypeRef = React.useRef(transactionType);
const fromCurrencyAmountRef = React.useRef(fromCurrencyAmount);
useEffect(() => {
pairRef.current = pair;
}, [pair]);
useEffect(() => {
transactionTypeRef.current = transactionTypeRef;
}, [transactionType]);
useEffect(() => {
fromCurrencyAmountRef.current = fromCurrencyAmount;
}, [fromCurrencyAmount]);
useEffect(() => {
handleInitPoll(pair, transactionType, fromCurrencyAmount);
const timer = setInterval(() => {
handleInitPoll(
pairRef.current,
transactionTypeRef.current,
fromCurrencyAmountRef.current
);
}, 6000);
return () => {
clearInterval(timer);
};
}, [pair, transactionType, fromCurrencyAmount]);
Fundamentally, your code seems to be correct with a few issues:
There is a race condition.
If getSwapPrice is running and the component is updated, it can still
affect the state when setSwapPriceInfo or setLoading are called when
the promise is resolved.
This is particularly bad, because network requests can "overtake" each
other. Thus it can happen that the return value of getSwapPrice
updates the component with the result of an old network request.
This is discussed in this article.
There is this odd call to setSelectedCurrencyState in the useEffect
block. It's not clear what this is supposed to do, but it clearly doesn't
belong there.
However, the underlying application should work fine, I reproduced it with a simpler application here:
import { useEffect, useState } from "react";
function fetchExchangeRateAsync(multiplier) {
return new Promise(resolve => {
setTimeout(() => {
resolve(Math.random() * multiplier);
}, 100);
});
}
function CurrencyExchangeRate() {
const [exchangeRate, setExchangeRate] = useState(null);
const [inputValueString, setInputValueString] = useState("");
const inputValue = Number(inputValueString);
const [multiplier, setMultiplier] = useState(1.0);
let outputValue = null;
if (!isNaN(inputValue) && exchangeRate !== null) {
outputValue = inputValue * exchangeRate;
}
useEffect(() => {
// To avoid race conditions, we must not update the state from an asynchronous operation if
// the component was re-rendered since then.
//
// https://overreacted.io/a-complete-guide-to-useeffect/
let didCancel = false;
// Do not delay the first request.
fetchExchangeRateAsync(multiplier)
.then(newExchangeRate => {
if (!didCancel) {
setExchangeRate(newExchangeRate);
}
});
// Poll exchange rate.
let intervalHandle = setInterval(() => {
fetchExchangeRateAsync(multiplier)
.then(newExchangeRate => {
if (!didCancel) {
setExchangeRate(newExchangeRate);
}
});
}, 500);
return () => {
didCancel = true;
clearInterval(intervalHandle);
};
}, [multiplier]);
return (
<div>
<input value={inputValueString} onChange={event => setInputValueString(event.target.value)} /><br />
<p>With current exchange rate: {outputValue !== null ? outputValue : "(loading)"}</p>
<button onClick={() => setMultiplier(100.0)}>Set Multiplier</button>
</div>
);
}
function App() {
return (
<CurrencyExchangeRate />
);
}
export default App;
This is quite a bit different from what you are doing but it does demonstrate that your code should generally work:
It is possible to trigger the fetch logic by changing the input field (here without debouncing) or in a given interval.
The fetch logic runs immediately when the component is rendered for the first time.
The "Set Multiplier" button can affect the value of multiplier and this information arrives in the setInterval call correctly.
This works because [multiplier] dictates that the effect should be re-run if that variable changes. When this happens, the old interval is first cleared with clearInterval and then re-started with setInterval.
In your case that would be pair, transactionType and fromCurrencyAmount instead of multiplier.
In other words, your issue seems to be outside the code that you provided in the question.
I have an issue with using Lodash + setInterval.
What I want to do:
Retrieve randomly one element of my object every 3 seconds
this is my object:
const [table, setTable]= useState ([]);
so I start with that:
const result = _.sample(table);
console.log(result);
console give => Object { label: "Figue", labelEn: "fig" }
But if a add :
const result = _.sample(table);
console.log(result.label);
console give => TypeError: result is undefined
Beside that I tried to add setInterval and also try with useEffect but or code crash or console give me two numbers every 3 second => 2,6,2,6 ......
Ciao, supposing that table object is correclty filled, you could use lodash and setInterval to get random object of table using useEffect and useRef hooks like:
const interval = useRef(null);
useEffect(() => {
if (!interval.current) {
interval.current = setInterval(() => {
const result = _.sample(table);
console.log(result.label);
}, 3000);
}
}, [table]);
Then to clean setInterval when component will be unmount you could use another useEffect in this way:
useEffect(() => {
return () => {
clearInterval(interval.current);
interval.current = null;
};
}, []);
EDIT
After your explanation, I found the cause of your problem. Before start setInterval you have to wait that table was filled with values (otherwise you get an error).
To solve that it's just necessary to put another condition on first useEffect (table.length > 0), and load data on second useEffect.
So the first useEffect becomes:
const interval = useRef(null);
useEffect(() => {
if (!interval.current && table.length > 0) {
interval.current = setInterval(() => {
const result = _.sample(table);
console.log(result.label);
}, 3000);
}
}, [table]);
And the second one:
useEffect(() => {
jsonbin.get("/b/5f3d58e44d93991036184474/5")
.then(({data}) => setTable(data));
return () => {
clearInterval(interval.current);
interval.current = null;
};
}, []);
Here the codesandbox updated.
The problem is that you access table before it is loaded.
You should either provide an initial value to that allows a successful do all your operations:
// use an array that has at least one element and a label as initial table value
const [table, setTable] = useState([{label: "default label"}]);
useEffect(() => {
jsonbin.get("/b/5f3d58e44d93991036184474/5")
.then(({data}) => setTable(data));
});
const result = _.sample(table);
console.log(result.label);
// ...
Or use an if or something alike to handle multiple scenarios:
// use an empty array as initial table value
const [table, setTable] = useState([]);
useEffect(() => {
jsonbin.get("/b/5f3d58e44d93991036184474/5")
.then(({data}) => setTable(data));
});
const result = _.sample(table);
// account for the initial empty table value by checking the result
// of _.sample which is `undefined` for empty arrays
if (result) {
console.log(result.label);
} else {
console.log("do something else");
}
// ...
If you fetch your data asynchronously you must think about what you want to use while the data is being fetched. The minimal thing to do is tell React to not render the component while the data is missing (being fetch).
const [table, setTable] = useState([]);
useEffect(() => {
jsonbin.get("/b/5f3d58e44d93991036184474/5")
.then(({data}) => setTable(data));
});
const result = _.sample(table);
if (!result) return null; // <- don't render if there is no result
console.log(result.label);
// ...
I have to monitoring some data update info on the screen each one or two seconds.
The way I figured that was using this implementation:
componentDidMount() {
this.timer = setInterval(()=> this.getItems(), 1000);
}
componentWillUnmount() {
this.timer = null;
}
getItems() {
fetch(this.getEndpoint('api url endpoint'))
.then(result => result.json())
.then(result => this.setState({ items: result }));
}
Is this the correct approach?
Well, since you have only an API and don't have control over it in order to change it to use sockets, the only way you have is to poll.
As per your polling is concerned, you're doing the decent approach. But there is one catch in your code above.
componentDidMount() {
this.timer = setInterval(()=> this.getItems(), 1000);
}
componentWillUnmount() {
this.timer = null; // here...
}
getItems() {
fetch(this.getEndpoint('api url endpoint'))
.then(result => result.json())
.then(result => this.setState({ items: result }));
}
The issue here is that once your component unmounts, though the reference to interval that you stored in this.timer is set to null, it is not stopped yet. The interval will keep invoking the handler even after your component has been unmounted and will try to setState in a component which no longer exists.
To handle it properly use clearInterval(this.timer) first and then set this.timer = null.
Also, the fetch call is asynchronous, which might cause the same issue. Make it cancelable and cancel if any fetch is incomplete.
I hope this helps.
Although an old question it was the top result when I searched for React Polling and didn't have an answer that worked with Hooks.
// utils.js
import React, { useState, useEffect, useRef } from 'react';
export const useInterval = (callback, delay) => {
const savedCallback = useRef();
useEffect(() => {
savedCallback.current = callback;
}, [callback]);
useEffect(() => {
function tick() {
savedCallback.current();
}
if (delay !== null) {
const id = setInterval(tick, delay);
return () => clearInterval(id);
}
}, [delay]);
}
Source: https://overreacted.io/making-setinterval-declarative-with-react-hooks/
You can then just import and use.
// MyPage.js
import useInterval from '../utils';
const MyPage = () => {
useInterval(() => {
// put your interval code here.
}, 1000 * 10);
return <div>my page content</div>;
}
You could use a combination of setTimeout and clearTimeout.
setInterval would fire the API call every 'x' seconds irrespective whether the previous call succeeded or failed. This can eat into your browser memory and degrade performance over time. Moreover, if the server is down, setInterval would continue to bombard the server not knowing its down status.
Whereas,
You could do a recursion using setTimeout. Fire a subsequent API call, only if the previous API call succeed. If previous call has failed, clear the timeout and do not fire any further calls. if required, alert the user on failure. Let the user refresh the page to restart this process.
Here is an example code:
let apiTimeout = setTimeout(fetchAPIData, 1000);
function fetchAPIData(){
fetch('API_END_POINT')
.then(res => {
if(res.statusCode == 200){
// Process the response and update the view.
// Recreate a setTimeout API call which will be fired after 1 second.
apiTimeout = setTimeout(fetchAPIData, 1000);
}else{
clearTimeout(apiTimeout);
// Failure case. If required, alert the user.
}
})
.fail(function(){
clearTimeout(apiTimeout);
// Failure case. If required, alert the user.
});
}
#AmitJS94, there's a detailed section on how to stop an interval that adds onto the methods that GavKilbride mentioned in this article.
The author says to add a state for a delay variable, and to pass in "null" for that delay when you want to pause the interval:
const [delay, setDelay] = useState(1000);
const [isRunning, setIsRunning] = useState(true);
useInterval(() => {
setCount(count + 1);
}, isRunning ? delay : null);
useEffect(() => {
function tick() {
savedCallback.current();
}
if (delay !== null) {
let id = setInterval(tick, delay);
return () => clearInterval(id);
}
}, [delay]);
Definitely read the article to get a better understanding of the details -- it's super thorough and well-written!
As Vasanth mention, I preferred to:
use setTimeout to measure the time between the end of the last request and the beginning of the next one
make the first request straight away, not after the delay
inspired by the answer from #KyleMit https://stackoverflow.com/a/64654157/343900
import { useEffect, useRef } from 'react';
export const useInterval = (
callback: Function,
fnCondition: Function,
delay: number,
) => {
const savedCallback = useRef<Function>();
useEffect(() => {
savedCallback.current = callback;
}, [callback]);
useEffect(() => {
let id: NodeJS.Timeout;
const tick = async () => {
try {
const response =
typeof savedCallback.current === 'function' &&
(await savedCallback.current());
if (fnCondition(response)) {
id = setTimeout(tick, delay);
} else {
clearTimeout(id);
}
} catch (e) {
console.error(e);
}
};
tick();
return () => id && clearTimeout(id);
// eslint-disable-next-line react-hooks/exhaustive-deps
}, [delay]);
};
WORKS: Using fnCondition inside which can be a condition based on the response from the last request.
//axios-hooks
const {
data,
isLoadingData,
getData,
} = api.useGetData();
const fnCondition = (result: any) => {
const randomContidion = Math.random();
//return true to continue
return randomContidion < 0.9;
};
useInterval(() => getData(), fnCondition, 1000);
DOES NOT WORK: Passing delay as null to stop useInterval like this does not work for me
with this code: https://www.aaron-powell.com/posts/2019-09-23-recursive-settimeout-with-react-hooks/
(You might get the impression it works, but after a few starts/stops it breaks)
const [isRunning, setIsRunning] = useState(true);
const handleOnclick = () => {
setIsRunning(!isRunning);
};
useInterval(() => getData(), isRunning ? 1000 : null);
<button onClick={handleOnclick}>{isRunning ? 'Stop' : 'Start'}</button>
Sum up: I'm able to stop useInterval by passing fnCondition, but not by passing delay=null
Here's a simple, full solution, that:
Polls every X seconds
Has the option of increasing the timeout each time the logic runs so you don't overload the server
Clears the timeouts when the end user exits the component
//mount data
componentDidMount() {
//run this function to get your data for the first time
this.getYourData();
//use the setTimeout to poll continuously, but each time increase the timer
this.timer = setTimeout(this.timeoutIncreaser, this.timeoutCounter);
}
//unmounting process
componentWillUnmount() {
this.timer = null; //clear variable
this.timeoutIncreaser = null; //clear function that resets timer
}
//increase by timeout by certain amount each time this is ran, and call fetchData() to reload screen
timeoutIncreaser = () => {
this.timeoutCounter += 1000 * 2; //increase timeout by 2 seconds every time
this.getYourData(); //this can be any function that you want ran every x seconds
setTimeout(this.timeoutIncreaser, this.timeoutCounter);
}
Here is a simple example using hooks in function component and this will refresh your data in a set interval.
import React from 'react';
import { useEffect, useState } from 'react';
export default function App() {
let [jokes, setJokes] = useState('Initial');
async function fetchJokes() {
let a = await fetch('https://api.chucknorris.io/jokes/random');
let b = await a.json();
setJokes(b.value);
}
// Below function works like compomentWillUnmount and hence it clears the timeout
useEffect(() => {
let id = setTimeout(fetchJokes, 2000);
return () => clearTimeout(id);
});
return <div>{jokes}</div>;
}
or, you can use axios as well to make the API calls.
function App() {
const [state, setState] = useState("Loading.....");
function fetchData() {
axios.get(`https://api.chucknorris.io/jokes/random`).then((response) => {
setState(response.data.value);
});
}
useEffect(() => {
console.log("Hi there!");
let timerId = setTimeout(fetchData, 2000);
return ()=> clearInterval(timerId);
});
return (
<>
This component
<h3>{state}</h3>
</>
);
}