i have a simple state and a function that runs in useEffect,
i setup the useEffect second argument to my updating state but seems to run in an endless loop
causing endless re-renders
const [file, setFile] = useState({audioFile: {} })
const loadAudioFromPath = (path) => {
import(`../components/Media/Resources/${path}`).then(audio =>
setFile({
audioFile: new Audio(audio),
})
);
}
useEffect(() => {
loadAudioFromPath(resourceURI)
console.log(file)
}, [file])
i also tried
useEffect(() => {
loadAudioFromPath(resourceURI)
console.log(file)
}, [])
still same issue!
EDIT: Try and change your useEffect to something like this:
Basically, add a boolean. If the boolean state changes then useEffect will fire.
const [file, setFile] = useState({audioFile: {} })
const [bool, setBool] = useState(false)
const loadAudioFromPath = (path) => {
import(`../components/Media/Resources/${path}`).then(audio =>
setFile({
audioFile: new Audio(audio),
})
if (file.length !== 0) {
setBool(true)
}
);
}
useEffect(() => {
loadAudioFromPath(resourceURI)
console.log(file)
}, [bool])
useEffect(() => {
loadAudioFromPath(resourceURI)
console.log(file)
}, [])
There must be some other issue in the code as:
useEffect(() => { loadAudioFromPath(resourceURI) console.log(file) }, [])
will only render once when the component loads. Happy to look into the rest of the code, if you add some more texture to the problem.
inspired by dr.Telma i fixed it by putting the result of the promise in a separate state then using that to create a new Audio and set it in the other state
const [file, setFile] = useState({audioFile: {} })
const [comp, setComp] = useState({audioComp: {} })
useEffect(() => {
import(`../components/Media/Resources/${resourceURI}`).then(audio =>
setComp({
audioComp: audio.default,
})
).then(()=>
setFile({
audioFile: new Audio(comp.audioComp),
})
)
}, [])
This is happeing because you are watching for file changes, and you are making changes in file using setFile inside of useEffect, so you made the loop.
So to help you more, i need to know what you really is trying to achivie with that file.
1 - If you trying to just load the file once it is uploaded you can try something like:
const { file, setFile } = useState();
const { resourceURI, setResourceURI } = useState();
useEffect(() => {
loadAudioFromPath(resourceURI)
}, [resourceURI])
const loadAudioFromPath = (path) => {
import(`../components/Media/Resources/${path}`).then(audio =>
setFile({
audioFile: new Audio(audio),
})
);
}
2 - If you trying to load the file just once (when the page is mounted)(Will do nothing if you change the file):
const { file, setFile } = useState();
useEffect(() => {
loadAudioFromPath(resourceURI);
}, [])
const loadAudioFromPath = (path) => {
import(`../components/Media/Resources/${path}`).then(audio =>
setFile({
audioFile: new Audio(audio),
})
);
}
3 - Or if you want to load the file if the current file is diferent than last one you can do something like i did in that answer -> A property is undefined - switching from class components to function hooks components in React
Related
I have been building a Laravel and React app and I had encountered something very embarassing.
The state variable context value is not changing with setState function. The code is following.
const ApiProvider = ({ children }) => {
const [data, setData] = React.useState({})
const [loading, setLoading] = React.useState(true)
const [repNumbers, setRepNumbers] = React.useState({})
useEffect(() => {
const fetchData = async() => {
}
fetchData()
return () => {
setData({})
}
}, [])
return <ApiContext.Provider value = {
{
repData: data,
loading,
repNumbers, //this is the state variable
setRepNumbers //this is the setState function
}
} > {
children
} <
/ApiContext.Provider>
}
In the consumming component
const { repData, repNumbers, setRepNumbers } = React.useContext(ApiContext)
const [pageLoading, setPageLoading] = React.useState(true)
useEffect(() => {
const fetchData = async () => {
setPageLoading(true)
await Axios({
})
.then((res) => {
setRepNumbers({...repNumbers, [id]: res.data })
setPageLoading(false)
return false
})
.catch((err) => {
return {}
})
return false
}
fetchData()
}, [])
If there are 2 consuming components, there should be 2 api calls and the repNumbers state should be mutated 2 times and add 2 id data but it only contains one id and if other call resolves, it replace the former id.
So how can I get both ids in repNumbers state?
This: ...but it only contains one id and if other call resolves, it replace the former id.
Assuming React 18 from your question. If so, React "Batches" updates. So although two updates were made, only the very last one was recorded.
This is dicussed in this blog post.
You can consider flushSync()
You might also consider refactoring your code to avoid the situation in the first place.
This question already has answers here:
The useState set method is not reflecting a change immediately
(15 answers)
Closed 1 year ago.
I try to give data with param using Route
and using param, get data from server and print it.
but useEffect doesn't work
export default function Board({ match }) {
const [content, setContent] = useState([]);
useEffect(() => {
getOnePost(match.params.number).then((response) => {
setContent(response);
});
console.log(content);
}, []);
return (
<div>
<div>hi</div>
</div>
);
}
<PrivateRoute
path="/board/:number"
authenticated={this.state.authenticated}
component={Board}
/>
I think you need to receive the url parameters from the useParams hook.
import { useParams } from "react-router-dom";
export default function Board() {
...
const { number } = useParams(); // get url parameters
useEffect(() => {
getOnePost(number).then((response) => {
setContent(response);
});
console.log(content);
}, []);
...
}
I think getonepost function is not defined as a async function. Please use this code.
useEffect(() => {
getOnePost(match.params.number).then((response) => {
setContent(response);
console.log(content);
});
}, []);
or you can try this either.
const [ update, setUpdate]=useState(true);
useEffect(() => {
console.log(content);
});
}, [update]);
getOnePost(match.params.number).then((response) => {
setContent(response);
setUpdate(!update);
}
You should pass match.params.number to useEffect as second argument.
useEffect(() => {
getOnePost(match.params.number).then((response) => {
setContent(response);
});
console.log(content);
}, [match.params.number]);
getOnePost is an asynchronous promise. So attempting to console.log(content) on the next line will not wait for the promise to resolve, and will log the initial value of [].
This is expected behaviour.
If you really want to log the value of content when it changes, add another useEffect with a dependency on content and put the console.log there.
export default function Board({ match }) {
const [content, setContent] = useState([]);
useEffect(() => {
getOnePost(match.params.number).then((response) => {
setContent(response);
});
}, []);
useEffect(() => {
console.log(content);
}, [content])
return (
<div>
<div>hi</div>
</div>
);
}
see, you are using console.log outside the .then statement, as you are writing asynchronous code it will console.log the content first then make a request to the server. if you want to see response, console.log it inside the then statement like this:-
const [content, setContent] = useState([]);
useEffect(() => {
getOnePost(match.params.number).then((response) => {
setContent(response);
console.log(response);
});
}, []);
and if you want to check weather it is stored in state or not you can do this:-
const [content, setContent] = useState([]);
useEffect(() => {
getOnePost(match.params.number).then((response) => {
setContent(response);
});
}, []);
useEffect(() => {
console.log(content)
}, [content])
the first useEffect run to get data from api and second run when content state changes.
I have the following case:
export default function Names() {
const dispatch = useDispatch();
const [names, setNames] = useState([]);
const stateNames = useSelector(state => state.names);
const fetchNames = async () => {
try {
const response = await nameService.getNames();
dispatch(initNames(response.body));
setNames(response.body);
} catch (error) {
console.error('Fetch Names: ', error);
}
};
useEffect(() => {
fetchNames();
}, []);
return (
{ names.map((name, index) => (
<Tab label={ budget.label} key={index}/>
)) }
);
}
When my component is rendered in the browser console I get a warning: "React Hook useEffect has a missing dependency: 'fetchBudgets'. Either include it or remove the dependency array react-hooks / exhaustive-deps".
If I comment the line in which I write the names in Redux state, the warning does not appear.
I need the list of names in the state so that I can update the list when a new name is written to the list from the outside.
export default function AddNameComponent() {
const dispatch = useDispatch();
const [label, setLabel] = useState('');
const [description, setDescription] = useState('');
const onLabelChange = (event) => { setLabel(event.target.value); };
const onDescriptionChange = (event) => { setDescription(event.target.value); };
const handleSubmit = async (event) => {
try {
event.preventDefault();
const newName = {
label: label
description: description
};
const answer = await budgetService.postNewName(newName);
dispatch(add(answer.body)); // Adding new Name in to Redux state.names
} catch (error) {
setErrorMessage(error.message);
console.error('Create Name: ', error);
}
};
return (
<div>
// Create name form
</div>
)
}
This is how everything works, but I don't understand why I have a warning.
I tried to add a flag to the array with dependencies of usеЕffect.
I tried to pass the function 'fetchNames' through the parent component - in props and to add it as a dependency, but it is executed twice ...
Can you advise please!
It's just an eslint warning so you don't have to fix it. But basically any variables which are used in the useEffect function are expected to be included in the dependency array. Otherwise, the effect will never be re-run even if the function fetchBudgets were to change.
It is expecting your hook to look like
useEffect(() => {
fetchBudgets();
}, [fetchBudgets]);
Where the effect will run once when the component is mounted and run again any time that the fetchBudgets function changes (which is probably never).
If it's executing more than once, that means that fetchBudgets has changed and you should try to figure our where and why it has been redefined. Maybe it needs to be memoized?
Here are the docs on putting functions in the dependency array.
Thanks for your attention! I tried many options and finally found one solution.
useEffect(() => {
async function fetchNames() {
const response = await nameService.getNames();
dispatch(init(response.body));
setNames(response.body);
}
fetchNames();
}, [dispatch, props]);
I put 'props' in an array of dependencies for one useEffect execution.
I am working on a small CRUD fullstack app with react and mongodb and I have this problem where I use useEffect to make an axios get request to the server to get all of my todos. The problem is that useEffect does it's job but it also rerenders to infinity. This is my component:
export default function () {
...
const [todos, setTodos] = useState([]);
const currentUser = JSON.parse(localStorage.getItem('user'))._id;
useEffect(() => {
async function populateTodos () {
try {
const res = await axios.get(`http://localhost:8000/api/all-todos/${currentUser}`);
setTodos(res.data);
} catch (err) {
if (err.response) {
console.log(err.response.data);
console.log(err.response.status);
console.log(err.response.headers);
} else if (err.request) {
console.log(err.request);
} else {
console.log('Error: ', err.message);
}
}
}
populateTodos();
}, [todos]);
console.log(todos);
return (
...
);
}
So what I was expecting to happen is that that console.log to get printed only when the todos changes, like when I add a new todo and so on, but instead it gets printed forever.
You said that you need to fetch todos at first, and whenever todos change. I can suggest you a different approach, using one more variable, something like this:
const TodosComponent = (props) => {
const [todos, setTodos] = useState([]);
const [updatedTodos, setUpdatesTodos] = useState(true);
const fetchFunction = () => {
// In here you implement your fetch, in which you call setTodos().
}
// Called on mount to fetch your todos.
useEffect(() => {
fetchFunction();
}, []);
// Used to updated todos when they have been updated.
useEffect(() => {
if (updatedTodos) {
fetchFunction();
setUpdatesTodos(false);
}
}, [updatedTodos]);
// Finally, wherever you update your todos, you also write `updateTodos(true)`.
}
I get this error:
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.
when fetching of data is started and component was unmounted, but function is trying to update state of unmounted component.
What is the best way to solve this?
CodePen example.
default function Test() {
const [notSeenAmount, setNotSeenAmount] = useState(false)
useEffect(() => {
let timer = setInterval(updateNotSeenAmount, 2000)
return () => clearInterval(timer)
}, [])
async function updateNotSeenAmount() {
let data // here i fetch data
setNotSeenAmount(data) // here is problem. If component was unmounted, i get error.
}
async function anotherFunction() {
updateNotSeenAmount() //it can trigger update too
}
return <button onClick={updateNotSeenAmount}>Push me</button> //update can be triggered manually
}
The easiest solution is to use a local variable that keeps track of whether the component is mounted or not. This is a common pattern with the class based approach. Here is an example that implement it with hooks:
function Example() {
const [text, setText] = React.useState("waiting...");
React.useEffect(() => {
let isCancelled = false;
simulateSlowNetworkRequest().then(() => {
if (!isCancelled) {
setText("done!");
}
});
return () => {
isCancelled = true;
};
}, []);
return <h2>{text}</h2>;
}
Here is an alternative with useRef (see below). Note that with a list of dependencies this solution won't work. The value of the ref will stay true after the first render. In that case the first solution is more appropriate.
function Example() {
const isCancelled = React.useRef(false);
const [text, setText] = React.useState("waiting...");
React.useEffect(() => {
fetch();
return () => {
isCancelled.current = true;
};
}, []);
function fetch() {
simulateSlowNetworkRequest().then(() => {
if (!isCancelled.current) {
setText("done!");
}
});
}
return <h2>{text}</h2>;
}
You can find more information about this pattern inside this article. Here is an issue inside the React project on GitHub that showcase this solution.
If you are fetching data from axios(using hooks) and the error still occurs, just wrap the setter inside the condition
let isRendered = useRef(false);
useEffect(() => {
isRendered = true;
axios
.get("/sample/api")
.then(res => {
if (isRendered) {
setState(res.data);
}
return null;
})
.catch(err => console.log(err));
return () => {
isRendered = false;
};
}, []);
TL;DR
Here is a CodeSandBox example
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.
Here is a simple solution for this. This warning is due to when we do some fetch request while that request is in the background (because some requests take some time.)and we navigate back from that screen then react cannot update the state. here is the example code for this. write this line before every state Update.
if(!isScreenMounted.current) return;
Here is Complete Example
import React , {useRef} from 'react'
import { Text,StatusBar,SafeAreaView,ScrollView, StyleSheet } from 'react-native'
import BASEURL from '../constants/BaseURL';
const SearchScreen = () => {
const isScreenMounted = useRef(true)
useEffect(() => {
return () => isScreenMounted.current = false
},[])
const ConvertFileSubmit = () => {
if(!isScreenMounted.current) return;
setUpLoading(true)
var formdata = new FormData();
var file = {
uri: `file://${route.params.selectedfiles[0].uri}`,
type:`${route.params.selectedfiles[0].minetype}`,
name:`${route.params.selectedfiles[0].displayname}`,
};
formdata.append("file",file);
fetch(`${BASEURL}/UploadFile`, {
method: 'POST',
body: formdata,
redirect: 'manual'
}).then(response => response.json())
.then(result => {
if(!isScreenMounted.current) return;
setUpLoading(false)
}).catch(error => {
console.log('error', error)
});
}
return(
<>
<StatusBar barStyle="dark-content" />
<SafeAreaView>
<ScrollView
contentInsetAdjustmentBehavior="automatic"
style={styles.scrollView}>
<Text>Search Screen</Text>
</ScrollView>
</SafeAreaView>
</>
)
}
export default SearchScreen;
const styles = StyleSheet.create({
scrollView: {
backgroundColor:"red",
},
container:{
flex:1,
justifyContent:"center",
alignItems:"center"
}
})
This answer is not related to the specific question but I got the same 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. and as a React newcomer could not find a solution to it.
My problem was related to useState in an unmounted component.
I noticed that I was calling a set state function (setIsLoading) after the function that unmounted my component:
const Login = () => {
const [isLoading, setIsLoading] = useState(false);
const handleLogin = () => {
setIsLoading(true);
firebase.auth().then(
functionToUnMountLoginSection();
// the problem is here
setIsLoading(false);
)
}
}
The correct way is to call setIsLoading when the component is still mounted, before calling the function to unmount/process user login in my specific case:
firebase.auth().then(
setIsLoading(false);
functionToUnMountLoginSection();
)
You add the state related datas into the useEffect body for not rerunning them every rerendering process. This method will solve the problem.
useEffect(() => {
let timer = setInterval(updateNotSeenAmount, 2000)
return () => clearInterval(timer)
}, [notSeenAmount])
REF: Tip: Optimizing Performance by Skipping Effects
Custom Hook Solution (ReactJs/NextJs)
Create a new folder named 'shared' and add two folders named 'hooks', 'utils' in it. Add a new file called 'commonFunctions.js' inside utils folder and add the code snippet below.
export const promisify = (fn) => {
return new Promise((resolve, reject) => {
fn
.then(response => resolve(response))
.catch(error => reject(error));
});
};
Add a new file called 'fetch-hook.js' inside hooks folder and add the code snippet below.
import { useCallback, useEffect, useRef } from "react";
import { promisify } from "../utils/commonFunctions";
export const useFetch = () => {
const isUnmounted = useRef(false);
useEffect(() => {
isUnmounted.current = false;
return () => {
isUnmounted.current = true;
};
}, []);
const call = useCallback((fn, onSuccess, onError = null) => {
promisify(fn).then(response => {
console.group('useFetch Hook response', response);
if (!isUnmounted.current) {
console.log('updating state..');
onSuccess(response.data);
}
else
console.log('aborted state update!');
console.groupEnd();
}).catch(error => {
console.log("useFetch Hook error", error);
if (!isUnmounted.current)
if (onError)
onError(error);
});
}, []);
return { call }
};
Folder Structure
Our custom hook is now ready. We use it in our component like below
const OurComponent = (props) => {
//..
const [subscriptions, setSubscriptions] = useState<any>([]);
//..
const { call } = useFetch();
// example method, change with your own
const getSubscriptions = useCallback(async () => {
call(
payment.companySubscriptions(userId), // example api call, change with your own
(data) => setSubscriptions(data),
);
}, [userId]);
//..
const updateSubscriptions = useCallback(async () => {
setTimeout(async () => {
await getSubscriptions();
}, 5000);// 5 seconds delay
}, [getSubscriptions]);
//..
}
In our component, we call 'updateSubscriptions' method. It will trigger 'getSubscriptions' method in which we used our custom hook. If we try to navigate to a different page after calling updateSubscriptions method before 5 seconds over, our custom hook will abort state update and prevent that warning on the title of this question
Wanna see opposite?
Change 'getSubscriptions' method with the one below
const getSubscriptions = useCallback(async () => {
const response = await payment.companySubscriptions(userId);
setSubscriptions(response);
}, [userId]);
Now try to call 'updateSubscriptions' method and navigate to a different page before 5 seconds over
Try this custom hook:
import { useEffect, useRef } from 'react';
export const useIsMounted = () => {
const isMounted = useRef(false);
useEffect(() => {
isMounted.current = true;
return () => (isMounted.current = false);
}, []);
return isMounted;
};
function Example() {
const isMounted = useIsMounted();
const [text, setText] = useState();
const safeSetState = useCallback((callback, ...args) => {
if (isMounted.current) {
callback(...args);
}
}, []);
useEffect(() => {
safeSetState(setText, 'Hello')
});
}, []);
return <h2>{text}</h2>;
}