React: how to asynchronously and sequentially remove elements from array state?

React: how to asynchronously and sequentially remove elements from array state? - javascript

I'm having hard time finding a way to solve quite simple problem in React:
import React, { useState } from 'react';
import './style.css';
const removeTodoFromDb = (todo) =>
new Promise((resolve) => {
setTimeout(resolve, 1000);
});
export default function App() {
const [todos, setTodos] = useState(['sleep', 'work', 'eat', 'play']);
const cleanup = async () => {
console.log('cleanup()');
if (todos.length) {
console.log('1', todos.join('|'));
todos[0] = todos[0] + '*';
setTodos((t) => todos.slice());
await removeTodoFromDb(todos.shift());
setTodos((t) => todos.slice());
cleanup();
console.log('2', todos.join('|'));
}
};
return (
<>
{todos.map((t, i) => (
<div key={i}>{t}</div>
))}
<button onClick={() => cleanup()}>Clean up</button>
</>
);
}
StackBlitz url: https://stackblitz.com/edit/react-aa6wde
I know todos, and setTodos loose references, but I cannot put cleanup() function into the useEffect block as it won't be exposed to the DOM.
What is the proper pattern for actions like this?
Thanks

If I understand correctly, you want to remove all elements of an array one after another, right?
If so, here's how I would write the cleanup function:
const cleanup = async () => {
if (!todos.length) return
// Use Promise.all to call removeTodoFromDb for ALL todos at the SAME time
await Promise.all(todos.map(todo => removeTodoFromDb(todo))
setTodos([])
};
Not sure you mean by this:
I know todos, and setTodos loose references, but I cannot put cleanup() function into the useEffect block as it won't be exposed to the DOM.

If you want put cleanup in useEffect just do it.
Activate useEffect when some boolean = true and with help onClick change it.

Related

Cannot retrieve current state inside async function in React.js

I have created some state at the top level component (App), however it seems that when this state is updated, the updated state is not read by the asynchronous function defined in useEffect() (it still uses the previous value), more detail below:
I am attempting to retrieve the state of the const processing in the async function toggleProcessing defined in useEffect(), so that when processing becomes false, the async function exits from the while loop. However, it seems that when the processing updates to false, the while loop still keeps executing.
The behaviour should be as follows: Pressing the 'Begin Processing' button should console log "Processing..." every two seconds, and when that same button is pressed again (now labeled 'Stop Processing'), then "Stopping Processing" should be console logged. However, in practice, "Stopping Processing" is never console logged, and "Processing" is continuously logged forever.
Below is the code:
import React, { useState, useEffect} from 'react'
const App = () => {
const [processing, setProcessing] = useState(false)
const sleep = (ms) => {
return new Promise(resolve => setTimeout(resolve, ms))
}
useEffect(() => {
const toggleProcessing = async () => {
while (processing) {
console.log('Processing...')
await sleep(2000);
}
console.log('Stopping Processing')
}
if (processing) {
toggleProcessing() // async function
}
}, [processing])
return (
<>
<button onClick={() => setProcessing(current => !current)}>{processing ? 'Stop Processing' : 'Begin Processing'}</button>
</>
)
}
export default App;
It really just comes down to being able to read the updated state of processing in the async function, but I have not figure out a way to do this, despite reading similar posts.
Thank you in advance!

If you wish to access a state when using timeouts, it's best to keep a reference to that variable. You can achieve this using the useRef hook. Simply add a ref with the processing value and remember to update it.
const [processing, setProcessing] = useState<boolean>(false);
const processingRef = useRef(null);
useEffect(() => {
processingRef.current = processing;
}, [processing]);

Here is the working code:
import React, { useState, useEffect, useRef} from 'react'
const App = () => {
const [processing, setProcessing] = useState(false)
const processingRef = useRef(null);
const sleep = (ms) => {
return new Promise(resolve => setTimeout(resolve, ms))
}
useEffect(() => {
const toggleProcessing = async () => {
while (processingRef.current) {
console.log('Processing')
await sleep(2000);
}
console.log('Stopping Processing')
}
processingRef.current = processing;
if (processing) {
toggleProcessing() // async function
}
}, [processing])
return (
<>
<button onClick={() => setProcessing(current => !current)}>{processing ? 'Stop Processing' : 'Begin Processing'}</button>
</>
)
}
export default App;

I was interested in how this works and exactly what your final solution was based on the accepted answer. I threw together a solution based on Dan Abramov's useInterval hook and figured this along with a link to some related resources might be useful to others.
I'm curious, is there any specific reason you decided to use setTimeout and introduce async/await and while loop rather than use setInterval? I wonder the implications. Will you handle clearTimeout on clean up in the effect if a timer is still running on unmount? What did your final solution look like?
Demo/Solution with useInterval
https://codesandbox.io/s/useinterval-example-processing-ik61ho
import React, { useState, useEffect, useRef } from "react";
const App = () => {
const [processing, setProcessing] = useState(false);
useInterval(() => console.log("processing"), 2000, processing);
return (
<div>
<button onClick={() => setProcessing((prev) => !prev)}>
{processing ? "Stop Processing" : "Begin Processing"}
</button>
</div>
);
};
function useInterval(callback, delay, processing) {
const callbackRef = useRef();
// Remember the latest callback.
useEffect(() => {
callbackRef.current = callback;
}, [callback]);
// Set up the interval.
useEffect(() => {
function tick() {
callbackRef.current();
}
if (delay !== null && processing) {
let id = setInterval(tick, delay);
console.log(`begin processing and timer with ID ${id} running...`);
// Clear timer on clean up.
return () => {
console.log(`clearing timer with ID ${id}`);
console.log("stopped");
clearInterval(id);
};
}
}, [delay, processing]);
}
export default App;
Relevant Links
Dan Abramov - Making setInterval Declarative with React Hooks
SO Question: React hooks - right way to clear timeouts and intervals
setTimeout and clearTimeout in React with Hooks (avoiding memory leaks by clearing timers on clean up in effects)

Calling setState in Axios async/await function [duplicate]

Problem
I am writing an application in React and was unable to avoid a super common pitfall, which is calling setState(...) after componentWillUnmount(...).
I looked very carefully at my code and tried to put some guarding clauses in place, but the problem persisted and I am still observing the warning.
Therefore, I've got two questions:
How do I figure out from the stack trace, which particular component and event handler or lifecycle hook is responsible for the rule violation?
Well, how to fix the problem itself, because my code was written with this pitfall in mind and is already trying to prevent it, but some underlying component's still generating the warning.
Browser console
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.
in TextLayerInternal (created by Context.Consumer)
in TextLayer (created by PageInternal) index.js:1446
d/console[e]
index.js:1446
warningWithoutStack
react-dom.development.js:520
warnAboutUpdateOnUnmounted
react-dom.development.js:18238
scheduleWork
react-dom.development.js:19684
enqueueSetState
react-dom.development.js:12936
./node_modules/react/cjs/react.development.js/Component.prototype.setState
react.development.js:356
_callee$
TextLayer.js:97
tryCatch
runtime.js:63
invoke
runtime.js:282
defineIteratorMethods/</prototype[method]
runtime.js:116
asyncGeneratorStep
asyncToGenerator.js:3
_throw
asyncToGenerator.js:29
Code
Book.tsx
import { throttle } from 'lodash';
import * as React from 'react';
import { AutoWidthPdf } from '../shared/AutoWidthPdf';
import BookCommandPanel from '../shared/BookCommandPanel';
import BookTextPath from '../static/pdf/sde.pdf';
import './Book.css';
const DEFAULT_WIDTH = 140;
class Book extends React.Component {
setDivSizeThrottleable: () => void;
pdfWrapper: HTMLDivElement | null = null;
isComponentMounted: boolean = false;
state = {
hidden: true,
pdfWidth: DEFAULT_WIDTH,
};
constructor(props: any) {
super(props);
this.setDivSizeThrottleable = throttle(
() => {
if (this.isComponentMounted) {
this.setState({
pdfWidth: this.pdfWrapper!.getBoundingClientRect().width - 5,
});
}
},
500,
);
}
componentDidMount = () => {
this.isComponentMounted = true;
this.setDivSizeThrottleable();
window.addEventListener("resize", this.setDivSizeThrottleable);
};
componentWillUnmount = () => {
this.isComponentMounted = false;
window.removeEventListener("resize", this.setDivSizeThrottleable);
};
render = () => (
<div className="Book">
{ this.state.hidden && <div className="Book__LoadNotification centered">Book is being loaded...</div> }
<div className={this.getPdfContentContainerClassName()}>
<BookCommandPanel
bookTextPath={BookTextPath}
/>
<div className="Book__PdfContent" ref={ref => this.pdfWrapper = ref}>
<AutoWidthPdf
file={BookTextPath}
width={this.state.pdfWidth}
onLoadSuccess={(_: any) => this.onDocumentComplete()}
/>
</div>
<BookCommandPanel
bookTextPath={BookTextPath}
/>
</div>
</div>
);
getPdfContentContainerClassName = () => this.state.hidden ? 'hidden' : '';
onDocumentComplete = () => {
try {
this.setState({ hidden: false });
this.setDivSizeThrottleable();
} catch (caughtError) {
console.warn({ caughtError });
}
};
}
export default Book;
AutoWidthPdf.tsx
import * as React from 'react';
import { Document, Page, pdfjs } from 'react-pdf';
pdfjs.GlobalWorkerOptions.workerSrc = `//cdnjs.cloudflare.com/ajax/libs/pdf.js/${pdfjs.version}/pdf.worker.js`;
interface IProps {
file: string;
width: number;
onLoadSuccess: (pdf: any) => void;
}
export class AutoWidthPdf extends React.Component<IProps> {
render = () => (
<Document
file={this.props.file}
onLoadSuccess={(_: any) => this.props.onLoadSuccess(_)}
>
<Page
pageNumber={1}
width={this.props.width}
/>
</Document>
);
}
Update 1: Cancel throttleable function (still no luck)
const DEFAULT_WIDTH = 140;
class Book extends React.Component {
setDivSizeThrottleable: ((() => void) & Cancelable) | undefined;
pdfWrapper: HTMLDivElement | null = null;
state = {
hidden: true,
pdfWidth: DEFAULT_WIDTH,
};
componentDidMount = () => {
this.setDivSizeThrottleable = throttle(
() => {
this.setState({
pdfWidth: this.pdfWrapper!.getBoundingClientRect().width - 5,
});
},
500,
);
this.setDivSizeThrottleable();
window.addEventListener("resize", this.setDivSizeThrottleable);
};
componentWillUnmount = () => {
window.removeEventListener("resize", this.setDivSizeThrottleable!);
this.setDivSizeThrottleable!.cancel();
this.setDivSizeThrottleable = undefined;
};
render = () => (
<div className="Book">
{ this.state.hidden && <div className="Book__LoadNotification centered">Book is being loaded...</div> }
<div className={this.getPdfContentContainerClassName()}>
<BookCommandPanel
BookTextPath={BookTextPath}
/>
<div className="Book__PdfContent" ref={ref => this.pdfWrapper = ref}>
<AutoWidthPdf
file={BookTextPath}
width={this.state.pdfWidth}
onLoadSuccess={(_: any) => this.onDocumentComplete()}
/>
</div>
<BookCommandPanel
BookTextPath={BookTextPath}
/>
</div>
</div>
);
getPdfContentContainerClassName = () => this.state.hidden ? 'hidden' : '';
onDocumentComplete = () => {
try {
this.setState({ hidden: false });
this.setDivSizeThrottleable!();
} catch (caughtError) {
console.warn({ caughtError });
}
};
}
export default Book;

Here is a React Hooks specific solution for
Error
Warning: Can't perform a React state update on an unmounted component.
Solution
You can declare let isMounted = true inside useEffect, which will be changed in the cleanup callback, as soon as the component is unmounted. Before state updates, you now check this variable conditionally:
useEffect(() => {
let isMounted = true; // note mutable flag
someAsyncOperation().then(data => {
if (isMounted) setState(data); // add conditional check
})
return () => { isMounted = false }; // cleanup toggles value, if unmounted
}, []); // adjust dependencies to your needs
const Parent = () => {
const [mounted, setMounted] = useState(true);
return (
<div>
Parent:
<button onClick={() => setMounted(!mounted)}>
{mounted ? "Unmount" : "Mount"} Child
</button>
{mounted && <Child />}
<p>
Unmount Child, while it is still loading. It won't set state later on,
so no error is triggered.
</p>
</div>
);
};
const Child = () => {
const [state, setState] = useState("loading (4 sec)...");
useEffect(() => {
let isMounted = true;
fetchData();
return () => {
isMounted = false;
};
// simulate some Web API fetching
function fetchData() {
setTimeout(() => {
// drop "if (isMounted)" to trigger error again
// (take IDE, doesn't work with stack snippet)
if (isMounted) setState("data fetched")
else console.log("aborted setState on unmounted component")
}, 4000);
}
}, []);
return <div>Child: {state}</div>;
};
ReactDOM.render(<Parent />, document.getElementById("root"));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.13.0/umd/react.production.min.js" integrity="sha256-32Gmw5rBDXyMjg/73FgpukoTZdMrxuYW7tj8adbN8z4=" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.13.0/umd/react-dom.production.min.js" integrity="sha256-bjQ42ac3EN0GqK40pC9gGi/YixvKyZ24qMP/9HiGW7w=" crossorigin="anonymous"></script>
<div id="root"></div>
<script>var { useReducer, useEffect, useState, useRef } = React</script>
Extension: Custom useAsync Hook
We can encapsulate all the boilerplate into a custom Hook, that automatically aborts async functions in case the component unmounts or dependency values have changed before:
function useAsync(asyncFn, onSuccess) {
useEffect(() => {
let isActive = true;
asyncFn().then(data => {
if (isActive) onSuccess(data);
});
return () => { isActive = false };
}, [asyncFn, onSuccess]);
}
// custom Hook for automatic abortion on unmount or dependency change
// You might add onFailure for promise errors as well.
function useAsync(asyncFn, onSuccess) {
useEffect(() => {
let isActive = true;
asyncFn().then(data => {
if (isActive) onSuccess(data)
else console.log("aborted setState on unmounted component")
});
return () => {
isActive = false;
};
}, [asyncFn, onSuccess]);
}
const Child = () => {
const [state, setState] = useState("loading (4 sec)...");
useAsync(simulateFetchData, setState);
return <div>Child: {state}</div>;
};
const Parent = () => {
const [mounted, setMounted] = useState(true);
return (
<div>
Parent:
<button onClick={() => setMounted(!mounted)}>
{mounted ? "Unmount" : "Mount"} Child
</button>
{mounted && <Child />}
<p>
Unmount Child, while it is still loading. It won't set state later on,
so no error is triggered.
</p>
</div>
);
};
const simulateFetchData = () => new Promise(
resolve => setTimeout(() => resolve("data fetched"), 4000));
ReactDOM.render(<Parent />, document.getElementById("root"));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.13.0/umd/react.production.min.js" integrity="sha256-32Gmw5rBDXyMjg/73FgpukoTZdMrxuYW7tj8adbN8z4=" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.13.0/umd/react-dom.production.min.js" integrity="sha256-bjQ42ac3EN0GqK40pC9gGi/YixvKyZ24qMP/9HiGW7w=" crossorigin="anonymous"></script>
<div id="root"></div>
<script>var { useReducer, useEffect, useState, useRef } = React</script>
More on effect cleanups: Overreacted: A Complete Guide to useEffect

To remove - Can't perform a React state update on an unmounted component warning, use componentDidMount method under a condition and make false that condition on componentWillUnmount method. For example : -
class Home extends Component {
_isMounted = false;
constructor(props) {
super(props);
this.state = {
news: [],
};
}
componentDidMount() {
this._isMounted = true;
ajaxVar
.get('https://domain')
.then(result => {
if (this._isMounted) {
this.setState({
news: result.data.hits,
});
}
});
}
componentWillUnmount() {
this._isMounted = false;
}
render() {
...
}
}

If above solutions dont work, try this and it works for me:
componentWillUnmount() {
// fix Warning: Can't perform a React state update on an unmounted component
this.setState = (state,callback)=>{
return;
};
}

There is a hook that's fairly common called useIsMounted that solves this problem (for functional components)...
import { useRef, useEffect } from 'react';
export function useIsMounted() {
const isMounted = useRef(false);
useEffect(() => {
isMounted.current = true;
return () => isMounted.current = false;
}, []);
return isMounted;
}
then in your functional component
function Book() {
const isMounted = useIsMounted();
...
useEffect(() => {
asyncOperation().then(data => {
if (isMounted.current) { setState(data); }
})
});
...
}

Checking if a component is mounted is actually an anti pattern as per React documentation. The solution to the setState warning is rather to leverage on the use of an AbortController:
useEffect(() => {
const abortController = new AbortController() // creating an AbortController
fetch(url, { signal: abortController.signal }) // passing the signal to the query
.then(data => {
setState(data) // if everything went well, set the state
})
.catch(error => {
if (error.name === 'AbortError') return // if the query has been aborted, do nothing
throw error
})
return () => {
abortController.abort() // stop the query by aborting on the AbortController on unmount
}
}, [])
For asynchronous operations that aren't based on the Fetch API, there still should be a way to cancel these asynchronous operations, and you should rather leverage these than just checking if a component is mounted. If you are building your own API, you can implement the AbortController API in it to handle it.
For more context, the check if a component is mounted is an anti pattern as React is checking internally if the component is mounted to display that warning. Doing the same check again is just a way to hide the warning, and there are some easier ways to hide them than adding this piece of code on a big part of a codebase.
Source: https://medium.com/doctolib/react-stop-checking-if-your-component-is-mounted-3bb2568a4934

I had this warning possibly because of calling setState from an effect hook (This is discussed in these 3 issues linked together).
Anyway, upgrading the react version removed the warning.

React already removed this warning
but here is a better solution (not just workaround)
useEffect(() => {
const abortController = new AbortController() // creating an AbortController
fetch(url, { signal: abortController.signal }) // passing the signal to the query
.then(data => {
setState(data) // if everything went well, set the state
})
.catch(error => {
if (error.name === 'AbortError') return // if the query has been aborted, do nothing
throw error
})
return () => {
abortController.abort()
}
}, [])

The solution from #ford04 didn't worked to me and specially if you need to use the isMounted in multiple places (multiple useEffect for instance), it's recommended to useRef, as bellow:
Essential packages
"dependencies":
{
"react": "17.0.1",
}
"devDependencies": {
"typescript": "4.1.5",
}
My Hook Component
export const SubscriptionsView: React.FC = () => {
const [data, setData] = useState<Subscription[]>();
const isMounted = React.useRef(true);
React.useEffect(() => {
if (isMounted.current) {
// fetch data
// setData (fetch result)
return () => {
isMounted.current = false;
};
}
}
});

try changing setDivSizeThrottleable to
this.setDivSizeThrottleable = throttle(
() => {
if (this.isComponentMounted) {
this.setState({
pdfWidth: this.pdfWrapper!.getBoundingClientRect().width - 5,
});
}
},
500,
{ leading: false, trailing: true }
);

I know that you're not using history, but in my case I was using the useHistory hook from React Router DOM, which unmounts the component before the state is persisted in my React Context Provider.
To fix this problem I have used the hook withRouter nesting the component, in my case export default withRouter(Login), and inside the component const Login = props => { ...; props.history.push("/dashboard"); .... I have also removed the other props.history.push from the component, e.g, if(authorization.token) return props.history.push('/dashboard') because this causes a loop, because the authorization state.
An alternative to push a new item to history.

Add a ref to a jsx component and then check it exist
function Book() {
const ref = useRef();
useEffect(() => {
asyncOperation().then(data => {
if (ref.current) setState(data);
})
});
return <div ref={ref}>content</div>
}

I had a similar issue thanks #ford04 helped me out.
However, another error occurred.
NB. I am using ReactJS hooks
ndex.js:1 Warning: Cannot update during an existing state transition (such as within `render`). Render methods should be a pure function of props and state.
What causes the error?
import {useHistory} from 'react-router-dom'
const History = useHistory()
if (true) {
history.push('/new-route');
}
return (
<>
<render component />
</>
)
This could not work because despite you are redirecting to new page all state and props are being manipulated on the dom or simply rendering to the previous page did not stop.
What solution I found
import {Redirect} from 'react-router-dom'
if (true) {
return <redirect to="/new-route" />
}
return (
<>
<render component />
</>
)

If you are fetching data from axios 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;
};
}, []);

I have 2 solutions for this error:
return:
If you are used hook and useEffect, So put a return end of useEffect.
useEffect(() => {
window.addEventListener('mousemove', logMouseMove)
return () => {
window.removeEventListener('mousemove', logMouseMove)
}
}, [])
componentWillUnmount:
If you are used componentDidMount, So put componentWillUnmount next to it.
componentDidMount() {
window.addEventListener('mousemove', this.logMouseMove)
}
componentWillUnmount() {
window.removeEventListener('mousemove', this.logMouseMove)
}

The isMounted approach is an anti-pattern in most cases because it doesn't actually clean up/cancel anything, it just avoids changing state on unmounted components, but does nothing with pending asynchronous tasks. The React team recently removed the leak warning because users keep creating a lot of anti-patterns to hide the warning rather than fix its cause.
But writing cancellable code in plain JS can be really tricky. To fix this I made my own lib useAsyncEffect2 with custom hooks, built on top of a cancellable promise (c-promise2) for executing cancellable async code to reach its graceful cancellation. All async stages (promises), including deep ones, are cancellable. This means that the request here will be automatically aborted if its parent context is canceled. Of course, any other asynchronous operation can be used instead of a request.
useAsyncEffect Demo with plain useState usage (Live Demo):
import React, { useState } from "react";
import { useAsyncEffect } from "use-async-effect2";
import cpAxios from "cp-axios";
function TestComponent({url}) {
const [text, setText] = useState("");
const cancel = useAsyncEffect(
function* () {
setText("fetching...");
const json = (yield cpAxios(url)).data;
setText(`Success: ${JSON.stringify(json)}`);
},
[url]
);
return (
<div>
<div>{text}</div>
<button onClick={cancel}>
Cancel request
</button>
</div>
);
}
useAsyncEffect Demo with internal states usage (Live Demo):
import React from "react";
import { useAsyncEffect } from "use-async-effect2";
import cpAxios from "cp-axios";
function TestComponent({ url, timeout }) {
const [cancel, done, result, err] = useAsyncEffect(
function* () {
return (yield cpAxios(url).timeout(timeout)).data;
},
{ states: true, deps: [url] }
);
return (
<div>
{done ? (err ? err.toString() : JSON.stringify(result)) : "loading..."}
<button onClick={cancel} disabled={done}>
Cancel async effect (abort request)
</button>
</div>
);
}
Class component using decorators (Live demo)
import React, { Component } from "react";
import { ReactComponent } from "c-promise2";
import cpAxios from "cp-axios";
#ReactComponent
class TestComponent extends Component {
state = {
text: ""
};
*componentDidMount(scope) {
const { url, timeout } = this.props;
const response = yield cpAxios(url).timeout(timeout);
this.setState({ text: JSON.stringify(response.data, null, 2) });
}
render() {
return (<div>{this.state.text}</div>);
}
}
export default TestComponent;
More other examples:
Axios request with errors handling
Fetch weather by coords
Live search
Pause & Resume
Progress capturing

Edit: I just realized the warning is referencing a component called TextLayerInternal. That's likely where your bug is. The rest of this is still relevant, but it might not fix your problem.
1) Getting the instance of a component for this warning is tough. It looks like there is some discussion to improve this in React but there currently is no easy way to do it. The reason it hasn't been built yet, I suspect, is likely because components are expected to be written in such a way that setState after unmount isn't possible no matter what the state of the component is. The problem, as far as the React team is concerned, is always in the Component code and not the Component instance, which is why you get the Component Type name.
That answer might be unsatisfactory, but I think I can fix your problem.
2) Lodashes throttled function has a cancel method. Call cancel in componentWillUnmount and ditch the isComponentMounted. Canceling is more "idiomatically" React than introducing a new property.

UPDATE DO NOT USE MY ORIGINAL ANSWER AS IT DOES NOT WORK
This answer was based on the use of cancelable promises and a note in makecancelable which I migrated to use hooks. However, it appears it does not cancel a chain of async/await and even cancelable-promise does not support canceling of a chain of awaits
Doing a bit more research on this, it appears that some internal Google reasons prevented cancelable promises from coming into the standard.
Further more, there was some promise with Bluebird which introduces cancelable promises, but it does not work in Expo or at least I haven't seen an example of it working in Expo.
The accepted answer is the best. Since I use TypeScript I had adapted the code with a few modifications (I explicitly set the dependencies since the accepted answer's implicit dependencies appear to give a re-render loop on my app, added and use async/await rather than promise chain, pass a ref to the mounted object so that an async/await chain can be canceled earlier if needed)
/**
* This starts an async function and executes another function that performs
* React state changes if the component is still mounted after the async
* operation completes
* #template T
* #param {(mountedRef: React.MutableRefObject<boolean>) => Promise<T>} asyncFunction async function,
* it has a copy of the mounted ref so an await chain can be canceled earlier.
* #param {(asyncResult: T) => void} onSuccess this gets executed after async
* function is resolved and the component is still mounted
* #param {import("react").DependencyList} deps
*/
export function useAsyncSetEffect(asyncFunction, onSuccess, deps) {
const mountedRef = useRef(false);
useEffect(() => {
mountedRef.current = true;
(async () => {
const x = await asyncFunction(mountedRef);
if (mountedRef.current) {
onSuccess(x);
}
})();
return () => {
mountedRef.current = false;
};
}, deps);
}
Original answer
Since I have many different operations that are async, I use the cancelable-promise package to resolve this issue with minimal code changes.
Previous code:
useEffect(() =>
(async () => {
const bar = await fooAsync();
setSomeState(bar);
})(),
[]
);
New code:
import { cancelable } from "cancelable-promise";
...
useEffect(
() => {
const cancelablePromise = cancelable(async () => {
const bar = await fooAsync();
setSomeState(bar);
})
return () => cancelablePromise.cancel();
},
[]
);
You can alsowrpte it in a custom utility function like this
/**
* This wraps an async function in a cancelable promise
* #param {() => PromiseLike<void>} asyncFunction
* #param {React.DependencyList} deps
*/
export function useCancelableEffect(asyncFunction, deps) {
useEffect(() => {
const cancelablePromise = cancelable(asyncFunction());
return () => cancelablePromise.cancel();
}, deps);
}

In my case of a login-like screen, the fetch was done in a onClick handler of a parent component, who passed that handler down to the child, whom placed .catch and .finally on it.
In the .then case a redirect (and hence unmount) would happen as normal operation, and only in cases of fetch error would the child stay mounted on-screen.
My solution was moving the setState and all other code from the .finally to the .catch since the child is guaranteed to be mounted in the .catch case. And in the .then case nothing needed doing because of the guaranteed unmount.

Based on #ford04 answer, here is the same encapsulated in a method :
import React, { FC, useState, useEffect, DependencyList } from 'react';
export function useEffectAsync( effectAsyncFun : ( isMounted: () => boolean ) => unknown, deps?: DependencyList ) {
useEffect( () => {
let isMounted = true;
const _unused = effectAsyncFun( () => isMounted );
return () => { isMounted = false; };
}, deps );
}
Usage:
const MyComponent : FC<{}> = (props) => {
const [ asyncProp , setAsyncProp ] = useState( '' ) ;
useEffectAsync( async ( isMounted ) =>
{
const someAsyncProp = await ... ;
if ( isMounted() )
setAsyncProp( someAsyncProp ) ;
});
return <div> ... ;
} ;

Depending on how you open your webpage, you may not be causing a mounting. Such as using a <Link/> back to a page that was already mounted in the virtual DOM, so requiring data from a componentDidMount lifecycle is caught.

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 they 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 the Complete Code
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"
}
})

I solved this problem by providing all the params that are used in the useEffect hook
The code reported the bug:
useEffect(() => {
getDistrict({
geonameid: countryId,
subdistrict: level,
}).then((res) => {
......
});
}, [countryId]);
The code after fix:
useEffect(() => {
getDistrict({
geonameid: countryId,
subdistrict: level,
}).then((res) => {
......
});
}, [countryId,level]);
Can see that , problems solved after I provided all the params(including the level param) that supposed to pass through.

I had a similar problem and solved it :
I was automatically making the user logged-in by dispatching an action on redux
( placing authentication token on redux state )
and then I was trying to show a message with this.setState({succ_message: "...")
in my component.
Component was looking empty with the same error on console : "unmounted component".."memory leak" etc.
After I read Walter's answer up in this thread
I've noticed that in the Routing table of my application ,
my component's route wasn't valid if user is logged-in :
{!this.props.user.token &&
<div>
<Route path="/register/:type" exact component={MyComp} />
</div>
}
I made the Route visible whether the token exists or not.

In my case the issue was that the parent component was hidding the child because of a condition change in the child component.
So what I did was to change the condition so the child component was always shown.
What was happening:
const ParentComponent:FC = () => {
...
if (someCondition) {
return null;
}
return (
<>
Some cool text here
<ChildModalComponent message="this is a cool modal" />
</>
)
}
const ChildModalComponent: FC = () => {
...
const handleSubmit = () => {
setSomeCondition(true);
}
}
So after clicking submit the modal was automatically hidden becasue of the parent condition (someCondition).
How did I fix it?
I changed the place where the someCondition was checked in the Parent component, so the child component was always shown:
const ParentComponent:FC = () => {
...
return (
<>
{!someCondition && <>Some cool text here</>
<ChildModalComponent message="this is a cool modal" />
</>
)
}

I faced same warning, not it is fixed. To fix the issue, I removed the useRef() variable check in useEffect()
Earlier, the code was
const varRef = useRef();
useEffect(() => {
if (!varRef.current)
{
}
}, []);
Now, the code is
const varRef = useRef();
useEffect(() => {
//if (!varRef.current)
{
}
}, [])
Hope, it helps...

Inspired by the accepted answer by #ford04 I had even better approach dealing with it, instead of using useEffect inside useAsync create a new function that returns a callback for componentWillUnmount :
function asyncRequest(asyncRequest, onSuccess, onError, onComplete) {
let isMounted=true
asyncRequest().then((data => isMounted ? onSuccess(data):null)).catch(onError).finally(onComplete)
return () => {isMounted=false}
}
...
useEffect(()=>{
return asyncRequest(()=>someAsyncTask(arg), response=> {
setSomeState(response)
},onError, onComplete)
},[])

const handleClick = async (item: NavheadersType, index: number) => {
const newNavHeaders = [...navheaders];
if (item.url) {
await router.push(item.url); =>>>> line causing error (causing route to happen)
// router.push(item.url); =>>> coreect line
newNavHeaders.forEach((item) => (item.active = false));
newNavHeaders[index].active = true;
setnavheaders([...newNavHeaders]);
}
};

The simplest and most compact solution (with an explanation) is seen below as a one-liner solution.
useEffect(() => { return () => {}; }, []);
The useEffect() example above returns a callback function triggers React to finish its unmount portion of its life-cycle prior to updating state.
That very simplistic solution is all that is needed. In addition, it also works unlike the fictional syntax provided by #ford04 and #sfletche . By the way, the below code snippet from #ford04 is purely imaginary syntax (#sfletche , #vinod , #guneetgstar , and #Drew Cordano used the very same imaginary syntax).
data => {       <--- Fictional/Imaginary Syntax
someAsyncOperation().then(data => {
if (isMounted) setState(data); // add conditional check
})
All of my linters and all the linters of my entire team will not accept it and they report Uncaught SyntaxError: unexpected token: '=>'. I am surprised that no one caught the imaginary syntax. Would anyone who has participated in this question-thread, particularly among the up-voters, explain to me how they got the solutions to work for them?

Inspired by #ford04 answer I use this hook, which also takes callbacks for success, errors, finally and an abortFn:
export const useAsync = (
asyncFn,
onSuccess = false,
onError = false,
onFinally = false,
abortFn = false
) => {
useEffect(() => {
let isMounted = true;
const run = async () => {
try{
let data = await asyncFn()
if (isMounted && onSuccess) onSuccess(data)
} catch(error) {
if (isMounted && onError) onSuccess(error)
} finally {
if (isMounted && onFinally) onFinally()
}
}
run()
return () => {
if(abortFn) abortFn()
isMounted = false
};
}, [asyncFn, onSuccess])
}
If the asyncFn is doing some kind of fetch from back-end it often makes sense to abort it when the component is unmounted (not always though, sometimes if ie. you're loading some data into a store you might as well just want to finish it even if component is unmounted)

How to cleanup a async call in react component useEffect after unmount? [duplicate]

Problem
I am writing an application in React and was unable to avoid a super common pitfall, which is calling setState(...) after componentWillUnmount(...).
I looked very carefully at my code and tried to put some guarding clauses in place, but the problem persisted and I am still observing the warning.
Therefore, I've got two questions:
How do I figure out from the stack trace, which particular component and event handler or lifecycle hook is responsible for the rule violation?
Well, how to fix the problem itself, because my code was written with this pitfall in mind and is already trying to prevent it, but some underlying component's still generating the warning.
Browser console
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.
in TextLayerInternal (created by Context.Consumer)
in TextLayer (created by PageInternal) index.js:1446
d/console[e]
index.js:1446
warningWithoutStack
react-dom.development.js:520
warnAboutUpdateOnUnmounted
react-dom.development.js:18238
scheduleWork
react-dom.development.js:19684
enqueueSetState
react-dom.development.js:12936
./node_modules/react/cjs/react.development.js/Component.prototype.setState
react.development.js:356
_callee$
TextLayer.js:97
tryCatch
runtime.js:63
invoke
runtime.js:282
defineIteratorMethods/</prototype[method]
runtime.js:116
asyncGeneratorStep
asyncToGenerator.js:3
_throw
asyncToGenerator.js:29
Code
Book.tsx
import { throttle } from 'lodash';
import * as React from 'react';
import { AutoWidthPdf } from '../shared/AutoWidthPdf';
import BookCommandPanel from '../shared/BookCommandPanel';
import BookTextPath from '../static/pdf/sde.pdf';
import './Book.css';
const DEFAULT_WIDTH = 140;
class Book extends React.Component {
setDivSizeThrottleable: () => void;
pdfWrapper: HTMLDivElement | null = null;
isComponentMounted: boolean = false;
state = {
hidden: true,
pdfWidth: DEFAULT_WIDTH,
};
constructor(props: any) {
super(props);
this.setDivSizeThrottleable = throttle(
() => {
if (this.isComponentMounted) {
this.setState({
pdfWidth: this.pdfWrapper!.getBoundingClientRect().width - 5,
});
}
},
500,
);
}
componentDidMount = () => {
this.isComponentMounted = true;
this.setDivSizeThrottleable();
window.addEventListener("resize", this.setDivSizeThrottleable);
};
componentWillUnmount = () => {
this.isComponentMounted = false;
window.removeEventListener("resize", this.setDivSizeThrottleable);
};
render = () => (
<div className="Book">
{ this.state.hidden && <div className="Book__LoadNotification centered">Book is being loaded...</div> }
<div className={this.getPdfContentContainerClassName()}>
<BookCommandPanel
bookTextPath={BookTextPath}
/>
<div className="Book__PdfContent" ref={ref => this.pdfWrapper = ref}>
<AutoWidthPdf
file={BookTextPath}
width={this.state.pdfWidth}
onLoadSuccess={(_: any) => this.onDocumentComplete()}
/>
</div>
<BookCommandPanel
bookTextPath={BookTextPath}
/>
</div>
</div>
);
getPdfContentContainerClassName = () => this.state.hidden ? 'hidden' : '';
onDocumentComplete = () => {
try {
this.setState({ hidden: false });
this.setDivSizeThrottleable();
} catch (caughtError) {
console.warn({ caughtError });
}
};
}
export default Book;
AutoWidthPdf.tsx
import * as React from 'react';
import { Document, Page, pdfjs } from 'react-pdf';
pdfjs.GlobalWorkerOptions.workerSrc = `//cdnjs.cloudflare.com/ajax/libs/pdf.js/${pdfjs.version}/pdf.worker.js`;
interface IProps {
file: string;
width: number;
onLoadSuccess: (pdf: any) => void;
}
export class AutoWidthPdf extends React.Component<IProps> {
render = () => (
<Document
file={this.props.file}
onLoadSuccess={(_: any) => this.props.onLoadSuccess(_)}
>
<Page
pageNumber={1}
width={this.props.width}
/>
</Document>
);
}
Update 1: Cancel throttleable function (still no luck)
const DEFAULT_WIDTH = 140;
class Book extends React.Component {
setDivSizeThrottleable: ((() => void) & Cancelable) | undefined;
pdfWrapper: HTMLDivElement | null = null;
state = {
hidden: true,
pdfWidth: DEFAULT_WIDTH,
};
componentDidMount = () => {
this.setDivSizeThrottleable = throttle(
() => {
this.setState({
pdfWidth: this.pdfWrapper!.getBoundingClientRect().width - 5,
});
},
500,
);
this.setDivSizeThrottleable();
window.addEventListener("resize", this.setDivSizeThrottleable);
};
componentWillUnmount = () => {
window.removeEventListener("resize", this.setDivSizeThrottleable!);
this.setDivSizeThrottleable!.cancel();
this.setDivSizeThrottleable = undefined;
};
render = () => (
<div className="Book">
{ this.state.hidden && <div className="Book__LoadNotification centered">Book is being loaded...</div> }
<div className={this.getPdfContentContainerClassName()}>
<BookCommandPanel
BookTextPath={BookTextPath}
/>
<div className="Book__PdfContent" ref={ref => this.pdfWrapper = ref}>
<AutoWidthPdf
file={BookTextPath}
width={this.state.pdfWidth}
onLoadSuccess={(_: any) => this.onDocumentComplete()}
/>
</div>
<BookCommandPanel
BookTextPath={BookTextPath}
/>
</div>
</div>
);
getPdfContentContainerClassName = () => this.state.hidden ? 'hidden' : '';
onDocumentComplete = () => {
try {
this.setState({ hidden: false });
this.setDivSizeThrottleable!();
} catch (caughtError) {
console.warn({ caughtError });
}
};
}
export default Book;

Here is a React Hooks specific solution for
Error
Warning: Can't perform a React state update on an unmounted component.
Solution
You can declare let isMounted = true inside useEffect, which will be changed in the cleanup callback, as soon as the component is unmounted. Before state updates, you now check this variable conditionally:
useEffect(() => {
let isMounted = true; // note mutable flag
someAsyncOperation().then(data => {
if (isMounted) setState(data); // add conditional check
})
return () => { isMounted = false }; // cleanup toggles value, if unmounted
}, []); // adjust dependencies to your needs
const Parent = () => {
const [mounted, setMounted] = useState(true);
return (
<div>
Parent:
<button onClick={() => setMounted(!mounted)}>
{mounted ? "Unmount" : "Mount"} Child
</button>
{mounted && <Child />}
<p>
Unmount Child, while it is still loading. It won't set state later on,
so no error is triggered.
</p>
</div>
);
};
const Child = () => {
const [state, setState] = useState("loading (4 sec)...");
useEffect(() => {
let isMounted = true;
fetchData();
return () => {
isMounted = false;
};
// simulate some Web API fetching
function fetchData() {
setTimeout(() => {
// drop "if (isMounted)" to trigger error again
// (take IDE, doesn't work with stack snippet)
if (isMounted) setState("data fetched")
else console.log("aborted setState on unmounted component")
}, 4000);
}
}, []);
return <div>Child: {state}</div>;
};
ReactDOM.render(<Parent />, document.getElementById("root"));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.13.0/umd/react.production.min.js" integrity="sha256-32Gmw5rBDXyMjg/73FgpukoTZdMrxuYW7tj8adbN8z4=" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.13.0/umd/react-dom.production.min.js" integrity="sha256-bjQ42ac3EN0GqK40pC9gGi/YixvKyZ24qMP/9HiGW7w=" crossorigin="anonymous"></script>
<div id="root"></div>
<script>var { useReducer, useEffect, useState, useRef } = React</script>
Extension: Custom useAsync Hook
We can encapsulate all the boilerplate into a custom Hook, that automatically aborts async functions in case the component unmounts or dependency values have changed before:
function useAsync(asyncFn, onSuccess) {
useEffect(() => {
let isActive = true;
asyncFn().then(data => {
if (isActive) onSuccess(data);
});
return () => { isActive = false };
}, [asyncFn, onSuccess]);
}
// custom Hook for automatic abortion on unmount or dependency change
// You might add onFailure for promise errors as well.
function useAsync(asyncFn, onSuccess) {
useEffect(() => {
let isActive = true;
asyncFn().then(data => {
if (isActive) onSuccess(data)
else console.log("aborted setState on unmounted component")
});
return () => {
isActive = false;
};
}, [asyncFn, onSuccess]);
}
const Child = () => {
const [state, setState] = useState("loading (4 sec)...");
useAsync(simulateFetchData, setState);
return <div>Child: {state}</div>;
};
const Parent = () => {
const [mounted, setMounted] = useState(true);
return (
<div>
Parent:
<button onClick={() => setMounted(!mounted)}>
{mounted ? "Unmount" : "Mount"} Child
</button>
{mounted && <Child />}
<p>
Unmount Child, while it is still loading. It won't set state later on,
so no error is triggered.
</p>
</div>
);
};
const simulateFetchData = () => new Promise(
resolve => setTimeout(() => resolve("data fetched"), 4000));
ReactDOM.render(<Parent />, document.getElementById("root"));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.13.0/umd/react.production.min.js" integrity="sha256-32Gmw5rBDXyMjg/73FgpukoTZdMrxuYW7tj8adbN8z4=" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.13.0/umd/react-dom.production.min.js" integrity="sha256-bjQ42ac3EN0GqK40pC9gGi/YixvKyZ24qMP/9HiGW7w=" crossorigin="anonymous"></script>
<div id="root"></div>
<script>var { useReducer, useEffect, useState, useRef } = React</script>
More on effect cleanups: Overreacted: A Complete Guide to useEffect

To remove - Can't perform a React state update on an unmounted component warning, use componentDidMount method under a condition and make false that condition on componentWillUnmount method. For example : -
class Home extends Component {
_isMounted = false;
constructor(props) {
super(props);
this.state = {
news: [],
};
}
componentDidMount() {
this._isMounted = true;
ajaxVar
.get('https://domain')
.then(result => {
if (this._isMounted) {
this.setState({
news: result.data.hits,
});
}
});
}
componentWillUnmount() {
this._isMounted = false;
}
render() {
...
}
}

If above solutions dont work, try this and it works for me:
componentWillUnmount() {
// fix Warning: Can't perform a React state update on an unmounted component
this.setState = (state,callback)=>{
return;
};
}

There is a hook that's fairly common called useIsMounted that solves this problem (for functional components)...
import { useRef, useEffect } from 'react';
export function useIsMounted() {
const isMounted = useRef(false);
useEffect(() => {
isMounted.current = true;
return () => isMounted.current = false;
}, []);
return isMounted;
}
then in your functional component
function Book() {
const isMounted = useIsMounted();
...
useEffect(() => {
asyncOperation().then(data => {
if (isMounted.current) { setState(data); }
})
});
...
}

Checking if a component is mounted is actually an anti pattern as per React documentation. The solution to the setState warning is rather to leverage on the use of an AbortController:
useEffect(() => {
const abortController = new AbortController() // creating an AbortController
fetch(url, { signal: abortController.signal }) // passing the signal to the query
.then(data => {
setState(data) // if everything went well, set the state
})
.catch(error => {
if (error.name === 'AbortError') return // if the query has been aborted, do nothing
throw error
})
return () => {
abortController.abort() // stop the query by aborting on the AbortController on unmount
}
}, [])
For asynchronous operations that aren't based on the Fetch API, there still should be a way to cancel these asynchronous operations, and you should rather leverage these than just checking if a component is mounted. If you are building your own API, you can implement the AbortController API in it to handle it.
For more context, the check if a component is mounted is an anti pattern as React is checking internally if the component is mounted to display that warning. Doing the same check again is just a way to hide the warning, and there are some easier ways to hide them than adding this piece of code on a big part of a codebase.
Source: https://medium.com/doctolib/react-stop-checking-if-your-component-is-mounted-3bb2568a4934

I had this warning possibly because of calling setState from an effect hook (This is discussed in these 3 issues linked together).
Anyway, upgrading the react version removed the warning.

React already removed this warning
but here is a better solution (not just workaround)
useEffect(() => {
const abortController = new AbortController() // creating an AbortController
fetch(url, { signal: abortController.signal }) // passing the signal to the query
.then(data => {
setState(data) // if everything went well, set the state
})
.catch(error => {
if (error.name === 'AbortError') return // if the query has been aborted, do nothing
throw error
})
return () => {
abortController.abort()
}
}, [])

The solution from #ford04 didn't worked to me and specially if you need to use the isMounted in multiple places (multiple useEffect for instance), it's recommended to useRef, as bellow:
Essential packages
"dependencies":
{
"react": "17.0.1",
}
"devDependencies": {
"typescript": "4.1.5",
}
My Hook Component
export const SubscriptionsView: React.FC = () => {
const [data, setData] = useState<Subscription[]>();
const isMounted = React.useRef(true);
React.useEffect(() => {
if (isMounted.current) {
// fetch data
// setData (fetch result)
return () => {
isMounted.current = false;
};
}
}
});

try changing setDivSizeThrottleable to
this.setDivSizeThrottleable = throttle(
() => {
if (this.isComponentMounted) {
this.setState({
pdfWidth: this.pdfWrapper!.getBoundingClientRect().width - 5,
});
}
},
500,
{ leading: false, trailing: true }
);

I know that you're not using history, but in my case I was using the useHistory hook from React Router DOM, which unmounts the component before the state is persisted in my React Context Provider.
To fix this problem I have used the hook withRouter nesting the component, in my case export default withRouter(Login), and inside the component const Login = props => { ...; props.history.push("/dashboard"); .... I have also removed the other props.history.push from the component, e.g, if(authorization.token) return props.history.push('/dashboard') because this causes a loop, because the authorization state.
An alternative to push a new item to history.

Add a ref to a jsx component and then check it exist
function Book() {
const ref = useRef();
useEffect(() => {
asyncOperation().then(data => {
if (ref.current) setState(data);
})
});
return <div ref={ref}>content</div>
}

I had a similar issue thanks #ford04 helped me out.
However, another error occurred.
NB. I am using ReactJS hooks
ndex.js:1 Warning: Cannot update during an existing state transition (such as within `render`). Render methods should be a pure function of props and state.
What causes the error?
import {useHistory} from 'react-router-dom'
const History = useHistory()
if (true) {
history.push('/new-route');
}
return (
<>
<render component />
</>
)
This could not work because despite you are redirecting to new page all state and props are being manipulated on the dom or simply rendering to the previous page did not stop.
What solution I found
import {Redirect} from 'react-router-dom'
if (true) {
return <redirect to="/new-route" />
}
return (
<>
<render component />
</>
)

If you are fetching data from axios 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;
};
}, []);

I have 2 solutions for this error:
return:
If you are used hook and useEffect, So put a return end of useEffect.
useEffect(() => {
window.addEventListener('mousemove', logMouseMove)
return () => {
window.removeEventListener('mousemove', logMouseMove)
}
}, [])
componentWillUnmount:
If you are used componentDidMount, So put componentWillUnmount next to it.
componentDidMount() {
window.addEventListener('mousemove', this.logMouseMove)
}
componentWillUnmount() {
window.removeEventListener('mousemove', this.logMouseMove)
}

The isMounted approach is an anti-pattern in most cases because it doesn't actually clean up/cancel anything, it just avoids changing state on unmounted components, but does nothing with pending asynchronous tasks. The React team recently removed the leak warning because users keep creating a lot of anti-patterns to hide the warning rather than fix its cause.
But writing cancellable code in plain JS can be really tricky. To fix this I made my own lib useAsyncEffect2 with custom hooks, built on top of a cancellable promise (c-promise2) for executing cancellable async code to reach its graceful cancellation. All async stages (promises), including deep ones, are cancellable. This means that the request here will be automatically aborted if its parent context is canceled. Of course, any other asynchronous operation can be used instead of a request.
useAsyncEffect Demo with plain useState usage (Live Demo):
import React, { useState } from "react";
import { useAsyncEffect } from "use-async-effect2";
import cpAxios from "cp-axios";
function TestComponent({url}) {
const [text, setText] = useState("");
const cancel = useAsyncEffect(
function* () {
setText("fetching...");
const json = (yield cpAxios(url)).data;
setText(`Success: ${JSON.stringify(json)}`);
},
[url]
);
return (
<div>
<div>{text}</div>
<button onClick={cancel}>
Cancel request
</button>
</div>
);
}
useAsyncEffect Demo with internal states usage (Live Demo):
import React from "react";
import { useAsyncEffect } from "use-async-effect2";
import cpAxios from "cp-axios";
function TestComponent({ url, timeout }) {
const [cancel, done, result, err] = useAsyncEffect(
function* () {
return (yield cpAxios(url).timeout(timeout)).data;
},
{ states: true, deps: [url] }
);
return (
<div>
{done ? (err ? err.toString() : JSON.stringify(result)) : "loading..."}
<button onClick={cancel} disabled={done}>
Cancel async effect (abort request)
</button>
</div>
);
}
Class component using decorators (Live demo)
import React, { Component } from "react";
import { ReactComponent } from "c-promise2";
import cpAxios from "cp-axios";
#ReactComponent
class TestComponent extends Component {
state = {
text: ""
};
*componentDidMount(scope) {
const { url, timeout } = this.props;
const response = yield cpAxios(url).timeout(timeout);
this.setState({ text: JSON.stringify(response.data, null, 2) });
}
render() {
return (<div>{this.state.text}</div>);
}
}
export default TestComponent;
More other examples:
Axios request with errors handling
Fetch weather by coords
Live search
Pause & Resume
Progress capturing

Edit: I just realized the warning is referencing a component called TextLayerInternal. That's likely where your bug is. The rest of this is still relevant, but it might not fix your problem.
1) Getting the instance of a component for this warning is tough. It looks like there is some discussion to improve this in React but there currently is no easy way to do it. The reason it hasn't been built yet, I suspect, is likely because components are expected to be written in such a way that setState after unmount isn't possible no matter what the state of the component is. The problem, as far as the React team is concerned, is always in the Component code and not the Component instance, which is why you get the Component Type name.
That answer might be unsatisfactory, but I think I can fix your problem.
2) Lodashes throttled function has a cancel method. Call cancel in componentWillUnmount and ditch the isComponentMounted. Canceling is more "idiomatically" React than introducing a new property.

UPDATE DO NOT USE MY ORIGINAL ANSWER AS IT DOES NOT WORK
This answer was based on the use of cancelable promises and a note in makecancelable which I migrated to use hooks. However, it appears it does not cancel a chain of async/await and even cancelable-promise does not support canceling of a chain of awaits
Doing a bit more research on this, it appears that some internal Google reasons prevented cancelable promises from coming into the standard.
Further more, there was some promise with Bluebird which introduces cancelable promises, but it does not work in Expo or at least I haven't seen an example of it working in Expo.
The accepted answer is the best. Since I use TypeScript I had adapted the code with a few modifications (I explicitly set the dependencies since the accepted answer's implicit dependencies appear to give a re-render loop on my app, added and use async/await rather than promise chain, pass a ref to the mounted object so that an async/await chain can be canceled earlier if needed)
/**
* This starts an async function and executes another function that performs
* React state changes if the component is still mounted after the async
* operation completes
* #template T
* #param {(mountedRef: React.MutableRefObject<boolean>) => Promise<T>} asyncFunction async function,
* it has a copy of the mounted ref so an await chain can be canceled earlier.
* #param {(asyncResult: T) => void} onSuccess this gets executed after async
* function is resolved and the component is still mounted
* #param {import("react").DependencyList} deps
*/
export function useAsyncSetEffect(asyncFunction, onSuccess, deps) {
const mountedRef = useRef(false);
useEffect(() => {
mountedRef.current = true;
(async () => {
const x = await asyncFunction(mountedRef);
if (mountedRef.current) {
onSuccess(x);
}
})();
return () => {
mountedRef.current = false;
};
}, deps);
}
Original answer
Since I have many different operations that are async, I use the cancelable-promise package to resolve this issue with minimal code changes.
Previous code:
useEffect(() =>
(async () => {
const bar = await fooAsync();
setSomeState(bar);
})(),
[]
);
New code:
import { cancelable } from "cancelable-promise";
...
useEffect(
() => {
const cancelablePromise = cancelable(async () => {
const bar = await fooAsync();
setSomeState(bar);
})
return () => cancelablePromise.cancel();
},
[]
);
You can alsowrpte it in a custom utility function like this
/**
* This wraps an async function in a cancelable promise
* #param {() => PromiseLike<void>} asyncFunction
* #param {React.DependencyList} deps
*/
export function useCancelableEffect(asyncFunction, deps) {
useEffect(() => {
const cancelablePromise = cancelable(asyncFunction());
return () => cancelablePromise.cancel();
}, deps);
}

In my case of a login-like screen, the fetch was done in a onClick handler of a parent component, who passed that handler down to the child, whom placed .catch and .finally on it.
In the .then case a redirect (and hence unmount) would happen as normal operation, and only in cases of fetch error would the child stay mounted on-screen.
My solution was moving the setState and all other code from the .finally to the .catch since the child is guaranteed to be mounted in the .catch case. And in the .then case nothing needed doing because of the guaranteed unmount.

Based on #ford04 answer, here is the same encapsulated in a method :
import React, { FC, useState, useEffect, DependencyList } from 'react';
export function useEffectAsync( effectAsyncFun : ( isMounted: () => boolean ) => unknown, deps?: DependencyList ) {
useEffect( () => {
let isMounted = true;
const _unused = effectAsyncFun( () => isMounted );
return () => { isMounted = false; };
}, deps );
}
Usage:
const MyComponent : FC<{}> = (props) => {
const [ asyncProp , setAsyncProp ] = useState( '' ) ;
useEffectAsync( async ( isMounted ) =>
{
const someAsyncProp = await ... ;
if ( isMounted() )
setAsyncProp( someAsyncProp ) ;
});
return <div> ... ;
} ;

Depending on how you open your webpage, you may not be causing a mounting. Such as using a <Link/> back to a page that was already mounted in the virtual DOM, so requiring data from a componentDidMount lifecycle is caught.

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 they 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 the Complete Code
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"
}
})

I solved this problem by providing all the params that are used in the useEffect hook
The code reported the bug:
useEffect(() => {
getDistrict({
geonameid: countryId,
subdistrict: level,
}).then((res) => {
......
});
}, [countryId]);
The code after fix:
useEffect(() => {
getDistrict({
geonameid: countryId,
subdistrict: level,
}).then((res) => {
......
});
}, [countryId,level]);
Can see that , problems solved after I provided all the params(including the level param) that supposed to pass through.

I had a similar problem and solved it :
I was automatically making the user logged-in by dispatching an action on redux
( placing authentication token on redux state )
and then I was trying to show a message with this.setState({succ_message: "...")
in my component.
Component was looking empty with the same error on console : "unmounted component".."memory leak" etc.
After I read Walter's answer up in this thread
I've noticed that in the Routing table of my application ,
my component's route wasn't valid if user is logged-in :
{!this.props.user.token &&
<div>
<Route path="/register/:type" exact component={MyComp} />
</div>
}
I made the Route visible whether the token exists or not.

In my case the issue was that the parent component was hidding the child because of a condition change in the child component.
So what I did was to change the condition so the child component was always shown.
What was happening:
const ParentComponent:FC = () => {
...
if (someCondition) {
return null;
}
return (
<>
Some cool text here
<ChildModalComponent message="this is a cool modal" />
</>
)
}
const ChildModalComponent: FC = () => {
...
const handleSubmit = () => {
setSomeCondition(true);
}
}
So after clicking submit the modal was automatically hidden becasue of the parent condition (someCondition).
How did I fix it?
I changed the place where the someCondition was checked in the Parent component, so the child component was always shown:
const ParentComponent:FC = () => {
...
return (
<>
{!someCondition && <>Some cool text here</>
<ChildModalComponent message="this is a cool modal" />
</>
)
}

I faced same warning, not it is fixed. To fix the issue, I removed the useRef() variable check in useEffect()
Earlier, the code was
const varRef = useRef();
useEffect(() => {
if (!varRef.current)
{
}
}, []);
Now, the code is
const varRef = useRef();
useEffect(() => {
//if (!varRef.current)
{
}
}, [])
Hope, it helps...

Inspired by the accepted answer by #ford04 I had even better approach dealing with it, instead of using useEffect inside useAsync create a new function that returns a callback for componentWillUnmount :
function asyncRequest(asyncRequest, onSuccess, onError, onComplete) {
let isMounted=true
asyncRequest().then((data => isMounted ? onSuccess(data):null)).catch(onError).finally(onComplete)
return () => {isMounted=false}
}
...
useEffect(()=>{
return asyncRequest(()=>someAsyncTask(arg), response=> {
setSomeState(response)
},onError, onComplete)
},[])

const handleClick = async (item: NavheadersType, index: number) => {
const newNavHeaders = [...navheaders];
if (item.url) {
await router.push(item.url); =>>>> line causing error (causing route to happen)
// router.push(item.url); =>>> coreect line
newNavHeaders.forEach((item) => (item.active = false));
newNavHeaders[index].active = true;
setnavheaders([...newNavHeaders]);
}
};

The simplest and most compact solution (with an explanation) is seen below as a one-liner solution.
useEffect(() => { return () => {}; }, []);
The useEffect() example above returns a callback function triggers React to finish its unmount portion of its life-cycle prior to updating state.
That very simplistic solution is all that is needed. In addition, it also works unlike the fictional syntax provided by #ford04 and #sfletche . By the way, the below code snippet from #ford04 is purely imaginary syntax (#sfletche , #vinod , #guneetgstar , and #Drew Cordano used the very same imaginary syntax).
data => {       <--- Fictional/Imaginary Syntax
someAsyncOperation().then(data => {
if (isMounted) setState(data); // add conditional check
})
All of my linters and all the linters of my entire team will not accept it and they report Uncaught SyntaxError: unexpected token: '=>'. I am surprised that no one caught the imaginary syntax. Would anyone who has participated in this question-thread, particularly among the up-voters, explain to me how they got the solutions to work for them?

Inspired by #ford04 answer I use this hook, which also takes callbacks for success, errors, finally and an abortFn:
export const useAsync = (
asyncFn,
onSuccess = false,
onError = false,
onFinally = false,
abortFn = false
) => {
useEffect(() => {
let isMounted = true;
const run = async () => {
try{
let data = await asyncFn()
if (isMounted && onSuccess) onSuccess(data)
} catch(error) {
if (isMounted && onError) onSuccess(error)
} finally {
if (isMounted && onFinally) onFinally()
}
}
run()
return () => {
if(abortFn) abortFn()
isMounted = false
};
}, [asyncFn, onSuccess])
}
If the asyncFn is doing some kind of fetch from back-end it often makes sense to abort it when the component is unmounted (not always though, sometimes if ie. you're loading some data into a store you might as well just want to finish it even if component is unmounted)

Preventing "not wrapped in act(...)" Jest warning when state update doesn't affect UI

I'm trying to figure out if there is a way to prevent the "not wrapped in act(...)" warning thrown by Jest/testing-library when I have nothing to assert after the state update that causes the warning happens, or if I should just ignore this warning.
Suppose I have this simple component:
import React, {useEffect, useState} from 'react';
import {getData} from 'services';
const MyComponent = () => {
const [arr, setArr] = useState([]);
useEffect(() => {
(async () => {
const {items} = await getData();
setArr(items);
})();
}, []);
return (
<div>
{!(arr.length > 0) && <p>no array items</p>}
{arr.length > 0 && (
<ul>
{arr.map(item => (
<li key={item.id}>{item.name}</li>
))}
</ul>
)}
</div>
);
};
export default MyComponent;
Suppose I want to simply test that this component renders okay even if getData() doesn't return any data for me.
So I have a test like this:
import React from 'react';
import {getData} from 'services';
import {render, screen} from 'testUtils';
import MyComponent from './MyComponent';
jest.mock('services', () => ({
getData: jest.fn(),
}));
it('renders', () => {
getData.mockResolvedValue({items: []});
render(<MyComponent />);
expect(screen.getByText('no array items')).toBeInTheDocument();
});
This test will pass, but I'll get the "not wrapped in act(...)" warning because the test will finish before getData() has a chance to finish.
In this case, the response from getData() sets arr to the same value (an empty array) as I have initially set it to at the top of the component. As such, my UI doesn't change after the async function completes—I'm still just looking at a paragraph that says "no array items"—so I don't really have anything I can assert that would wait for the state update to complete.
I can expect(getData).toHaveBeenCalledTimes(1), but that doesn't wait for the state to actually be updated after the function call.
I have attempted an arbitrary pause in the test to allow time for setArr(items) to happen:
it('renders', async () => {
getData.mockResolvedValue({items: []});
render(<MyComponent />);
expect(screen.getByText('no array items')).toBeInTheDocument();
await new Promise(resolve => setTimeout(resolve, 2000));
expect(screen.getByText('no array items')).toBeInTheDocument();
});
But that doesn't seem to help, and I'm honestly not sure why.
Is there a way to handle this situation by modifying only the test?
I am sure I could fix the problem by refactoring MyComponent, e.g., by passing arr to MyComponent as a prop and moving the getData() call to a parent component, or creating some custom prop used only for testing that would skip the getData() call altogether, but I don't want to be modifying components purely to avoid warnings in tests.
I am using testing-library/react, v11.2.2.

You can use findByText (a combination of getByText and waitFor) to ensure all updates have happened when the assertion resolves.
it('renders', async () => {
getData.mockResolvedValue({items: []});
render(<MyComponent />);
expect(await screen.findByText('no array items')).toBeInTheDocument();
});

#juliomalves's answer is spot on.
However, I had to put this await in my beforeEach:
import {render, fireEvent} from '#testing-library/react';
import MyComponent from './MyComponent';
...
describe('MyComponent should', () => {
let getByText, getByTestId, getAllByTestId, getByLabelText;
beforeEach(async () => {
let findByText;
({
getByText,
getByTestId,
getAllByTestId,
getByLabelText,
findByText,
} = render(<MyComponent {...props} />));
// Have this here to avoid warnings because of setting state variables
await findByText('no array items');
})
...
});

Can't perform a React state update on an unmounted component

Problem
I am writing an application in React and was unable to avoid a super common pitfall, which is calling setState(...) after componentWillUnmount(...).
I looked very carefully at my code and tried to put some guarding clauses in place, but the problem persisted and I am still observing the warning.
Therefore, I've got two questions:
How do I figure out from the stack trace, which particular component and event handler or lifecycle hook is responsible for the rule violation?
Well, how to fix the problem itself, because my code was written with this pitfall in mind and is already trying to prevent it, but some underlying component's still generating the warning.
Browser console
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.
in TextLayerInternal (created by Context.Consumer)
in TextLayer (created by PageInternal) index.js:1446
d/console[e]
index.js:1446
warningWithoutStack
react-dom.development.js:520
warnAboutUpdateOnUnmounted
react-dom.development.js:18238
scheduleWork
react-dom.development.js:19684
enqueueSetState
react-dom.development.js:12936
./node_modules/react/cjs/react.development.js/Component.prototype.setState
react.development.js:356
_callee$
TextLayer.js:97
tryCatch
runtime.js:63
invoke
runtime.js:282
defineIteratorMethods/</prototype[method]
runtime.js:116
asyncGeneratorStep
asyncToGenerator.js:3
_throw
asyncToGenerator.js:29
Code
Book.tsx
import { throttle } from 'lodash';
import * as React from 'react';
import { AutoWidthPdf } from '../shared/AutoWidthPdf';
import BookCommandPanel from '../shared/BookCommandPanel';
import BookTextPath from '../static/pdf/sde.pdf';
import './Book.css';
const DEFAULT_WIDTH = 140;
class Book extends React.Component {
setDivSizeThrottleable: () => void;
pdfWrapper: HTMLDivElement | null = null;
isComponentMounted: boolean = false;
state = {
hidden: true,
pdfWidth: DEFAULT_WIDTH,
};
constructor(props: any) {
super(props);
this.setDivSizeThrottleable = throttle(
() => {
if (this.isComponentMounted) {
this.setState({
pdfWidth: this.pdfWrapper!.getBoundingClientRect().width - 5,
});
}
},
500,
);
}
componentDidMount = () => {
this.isComponentMounted = true;
this.setDivSizeThrottleable();
window.addEventListener("resize", this.setDivSizeThrottleable);
};
componentWillUnmount = () => {
this.isComponentMounted = false;
window.removeEventListener("resize", this.setDivSizeThrottleable);
};
render = () => (
<div className="Book">
{ this.state.hidden && <div className="Book__LoadNotification centered">Book is being loaded...</div> }
<div className={this.getPdfContentContainerClassName()}>
<BookCommandPanel
bookTextPath={BookTextPath}
/>
<div className="Book__PdfContent" ref={ref => this.pdfWrapper = ref}>
<AutoWidthPdf
file={BookTextPath}
width={this.state.pdfWidth}
onLoadSuccess={(_: any) => this.onDocumentComplete()}
/>
</div>
<BookCommandPanel
bookTextPath={BookTextPath}
/>
</div>
</div>
);
getPdfContentContainerClassName = () => this.state.hidden ? 'hidden' : '';
onDocumentComplete = () => {
try {
this.setState({ hidden: false });
this.setDivSizeThrottleable();
} catch (caughtError) {
console.warn({ caughtError });
}
};
}
export default Book;
AutoWidthPdf.tsx
import * as React from 'react';
import { Document, Page, pdfjs } from 'react-pdf';
pdfjs.GlobalWorkerOptions.workerSrc = `//cdnjs.cloudflare.com/ajax/libs/pdf.js/${pdfjs.version}/pdf.worker.js`;
interface IProps {
file: string;
width: number;
onLoadSuccess: (pdf: any) => void;
}
export class AutoWidthPdf extends React.Component<IProps> {
render = () => (
<Document
file={this.props.file}
onLoadSuccess={(_: any) => this.props.onLoadSuccess(_)}
>
<Page
pageNumber={1}
width={this.props.width}
/>
</Document>
);
}
Update 1: Cancel throttleable function (still no luck)
const DEFAULT_WIDTH = 140;
class Book extends React.Component {
setDivSizeThrottleable: ((() => void) & Cancelable) | undefined;
pdfWrapper: HTMLDivElement | null = null;
state = {
hidden: true,
pdfWidth: DEFAULT_WIDTH,
};
componentDidMount = () => {
this.setDivSizeThrottleable = throttle(
() => {
this.setState({
pdfWidth: this.pdfWrapper!.getBoundingClientRect().width - 5,
});
},
500,
);
this.setDivSizeThrottleable();
window.addEventListener("resize", this.setDivSizeThrottleable);
};
componentWillUnmount = () => {
window.removeEventListener("resize", this.setDivSizeThrottleable!);
this.setDivSizeThrottleable!.cancel();
this.setDivSizeThrottleable = undefined;
};
render = () => (
<div className="Book">
{ this.state.hidden && <div className="Book__LoadNotification centered">Book is being loaded...</div> }
<div className={this.getPdfContentContainerClassName()}>
<BookCommandPanel
BookTextPath={BookTextPath}
/>
<div className="Book__PdfContent" ref={ref => this.pdfWrapper = ref}>
<AutoWidthPdf
file={BookTextPath}
width={this.state.pdfWidth}
onLoadSuccess={(_: any) => this.onDocumentComplete()}
/>
</div>
<BookCommandPanel
BookTextPath={BookTextPath}
/>
</div>
</div>
);
getPdfContentContainerClassName = () => this.state.hidden ? 'hidden' : '';
onDocumentComplete = () => {
try {
this.setState({ hidden: false });
this.setDivSizeThrottleable!();
} catch (caughtError) {
console.warn({ caughtError });
}
};
}
export default Book;

Here is a React Hooks specific solution for
Error
Warning: Can't perform a React state update on an unmounted component.
Solution
You can declare let isMounted = true inside useEffect, which will be changed in the cleanup callback, as soon as the component is unmounted. Before state updates, you now check this variable conditionally:
useEffect(() => {
let isMounted = true; // note mutable flag
someAsyncOperation().then(data => {
if (isMounted) setState(data); // add conditional check
})
return () => { isMounted = false }; // cleanup toggles value, if unmounted
}, []); // adjust dependencies to your needs
const Parent = () => {
const [mounted, setMounted] = useState(true);
return (
<div>
Parent:
<button onClick={() => setMounted(!mounted)}>
{mounted ? "Unmount" : "Mount"} Child
</button>
{mounted && <Child />}
<p>
Unmount Child, while it is still loading. It won't set state later on,
so no error is triggered.
</p>
</div>
);
};
const Child = () => {
const [state, setState] = useState("loading (4 sec)...");
useEffect(() => {
let isMounted = true;
fetchData();
return () => {
isMounted = false;
};
// simulate some Web API fetching
function fetchData() {
setTimeout(() => {
// drop "if (isMounted)" to trigger error again
// (take IDE, doesn't work with stack snippet)
if (isMounted) setState("data fetched")
else console.log("aborted setState on unmounted component")
}, 4000);
}
}, []);
return <div>Child: {state}</div>;
};
ReactDOM.render(<Parent />, document.getElementById("root"));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.13.0/umd/react.production.min.js" integrity="sha256-32Gmw5rBDXyMjg/73FgpukoTZdMrxuYW7tj8adbN8z4=" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.13.0/umd/react-dom.production.min.js" integrity="sha256-bjQ42ac3EN0GqK40pC9gGi/YixvKyZ24qMP/9HiGW7w=" crossorigin="anonymous"></script>
<div id="root"></div>
<script>var { useReducer, useEffect, useState, useRef } = React</script>
Extension: Custom useAsync Hook
We can encapsulate all the boilerplate into a custom Hook, that automatically aborts async functions in case the component unmounts or dependency values have changed before:
function useAsync(asyncFn, onSuccess) {
useEffect(() => {
let isActive = true;
asyncFn().then(data => {
if (isActive) onSuccess(data);
});
return () => { isActive = false };
}, [asyncFn, onSuccess]);
}
// custom Hook for automatic abortion on unmount or dependency change
// You might add onFailure for promise errors as well.
function useAsync(asyncFn, onSuccess) {
useEffect(() => {
let isActive = true;
asyncFn().then(data => {
if (isActive) onSuccess(data)
else console.log("aborted setState on unmounted component")
});
return () => {
isActive = false;
};
}, [asyncFn, onSuccess]);
}
const Child = () => {
const [state, setState] = useState("loading (4 sec)...");
useAsync(simulateFetchData, setState);
return <div>Child: {state}</div>;
};
const Parent = () => {
const [mounted, setMounted] = useState(true);
return (
<div>
Parent:
<button onClick={() => setMounted(!mounted)}>
{mounted ? "Unmount" : "Mount"} Child
</button>
{mounted && <Child />}
<p>
Unmount Child, while it is still loading. It won't set state later on,
so no error is triggered.
</p>
</div>
);
};
const simulateFetchData = () => new Promise(
resolve => setTimeout(() => resolve("data fetched"), 4000));
ReactDOM.render(<Parent />, document.getElementById("root"));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.13.0/umd/react.production.min.js" integrity="sha256-32Gmw5rBDXyMjg/73FgpukoTZdMrxuYW7tj8adbN8z4=" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.13.0/umd/react-dom.production.min.js" integrity="sha256-bjQ42ac3EN0GqK40pC9gGi/YixvKyZ24qMP/9HiGW7w=" crossorigin="anonymous"></script>
<div id="root"></div>
<script>var { useReducer, useEffect, useState, useRef } = React</script>
More on effect cleanups: Overreacted: A Complete Guide to useEffect

To remove - Can't perform a React state update on an unmounted component warning, use componentDidMount method under a condition and make false that condition on componentWillUnmount method. For example : -
class Home extends Component {
_isMounted = false;
constructor(props) {
super(props);
this.state = {
news: [],
};
}
componentDidMount() {
this._isMounted = true;
ajaxVar
.get('https://domain')
.then(result => {
if (this._isMounted) {
this.setState({
news: result.data.hits,
});
}
});
}
componentWillUnmount() {
this._isMounted = false;
}
render() {
...
}
}

If above solutions dont work, try this and it works for me:
componentWillUnmount() {
// fix Warning: Can't perform a React state update on an unmounted component
this.setState = (state,callback)=>{
return;
};
}

There is a hook that's fairly common called useIsMounted that solves this problem (for functional components)...
import { useRef, useEffect } from 'react';
export function useIsMounted() {
const isMounted = useRef(false);
useEffect(() => {
isMounted.current = true;
return () => isMounted.current = false;
}, []);
return isMounted;
}
then in your functional component
function Book() {
const isMounted = useIsMounted();
...
useEffect(() => {
asyncOperation().then(data => {
if (isMounted.current) { setState(data); }
})
});
...
}

Checking if a component is mounted is actually an anti pattern as per React documentation. The solution to the setState warning is rather to leverage on the use of an AbortController:
useEffect(() => {
const abortController = new AbortController() // creating an AbortController
fetch(url, { signal: abortController.signal }) // passing the signal to the query
.then(data => {
setState(data) // if everything went well, set the state
})
.catch(error => {
if (error.name === 'AbortError') return // if the query has been aborted, do nothing
throw error
})
return () => {
abortController.abort() // stop the query by aborting on the AbortController on unmount
}
}, [])
For asynchronous operations that aren't based on the Fetch API, there still should be a way to cancel these asynchronous operations, and you should rather leverage these than just checking if a component is mounted. If you are building your own API, you can implement the AbortController API in it to handle it.
For more context, the check if a component is mounted is an anti pattern as React is checking internally if the component is mounted to display that warning. Doing the same check again is just a way to hide the warning, and there are some easier ways to hide them than adding this piece of code on a big part of a codebase.
Source: https://medium.com/doctolib/react-stop-checking-if-your-component-is-mounted-3bb2568a4934

I had this warning possibly because of calling setState from an effect hook (This is discussed in these 3 issues linked together).
Anyway, upgrading the react version removed the warning.

React already removed this warning
but here is a better solution (not just workaround)
useEffect(() => {
const abortController = new AbortController() // creating an AbortController
fetch(url, { signal: abortController.signal }) // passing the signal to the query
.then(data => {
setState(data) // if everything went well, set the state
})
.catch(error => {
if (error.name === 'AbortError') return // if the query has been aborted, do nothing
throw error
})
return () => {
abortController.abort()
}
}, [])

The solution from #ford04 didn't worked to me and specially if you need to use the isMounted in multiple places (multiple useEffect for instance), it's recommended to useRef, as bellow:
Essential packages
"dependencies":
{
"react": "17.0.1",
}
"devDependencies": {
"typescript": "4.1.5",
}
My Hook Component
export const SubscriptionsView: React.FC = () => {
const [data, setData] = useState<Subscription[]>();
const isMounted = React.useRef(true);
React.useEffect(() => {
if (isMounted.current) {
// fetch data
// setData (fetch result)
return () => {
isMounted.current = false;
};
}
}
});

try changing setDivSizeThrottleable to
this.setDivSizeThrottleable = throttle(
() => {
if (this.isComponentMounted) {
this.setState({
pdfWidth: this.pdfWrapper!.getBoundingClientRect().width - 5,
});
}
},
500,
{ leading: false, trailing: true }
);

I know that you're not using history, but in my case I was using the useHistory hook from React Router DOM, which unmounts the component before the state is persisted in my React Context Provider.
To fix this problem I have used the hook withRouter nesting the component, in my case export default withRouter(Login), and inside the component const Login = props => { ...; props.history.push("/dashboard"); .... I have also removed the other props.history.push from the component, e.g, if(authorization.token) return props.history.push('/dashboard') because this causes a loop, because the authorization state.
An alternative to push a new item to history.

Add a ref to a jsx component and then check it exist
function Book() {
const ref = useRef();
useEffect(() => {
asyncOperation().then(data => {
if (ref.current) setState(data);
})
});
return <div ref={ref}>content</div>
}

I had a similar issue thanks #ford04 helped me out.
However, another error occurred.
NB. I am using ReactJS hooks
ndex.js:1 Warning: Cannot update during an existing state transition (such as within `render`). Render methods should be a pure function of props and state.
What causes the error?
import {useHistory} from 'react-router-dom'
const History = useHistory()
if (true) {
history.push('/new-route');
}
return (
<>
<render component />
</>
)
This could not work because despite you are redirecting to new page all state and props are being manipulated on the dom or simply rendering to the previous page did not stop.
What solution I found
import {Redirect} from 'react-router-dom'
if (true) {
return <redirect to="/new-route" />
}
return (
<>
<render component />
</>
)

If you are fetching data from axios 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;
};
}, []);

I have 2 solutions for this error:
return:
If you are used hook and useEffect, So put a return end of useEffect.
useEffect(() => {
window.addEventListener('mousemove', logMouseMove)
return () => {
window.removeEventListener('mousemove', logMouseMove)
}
}, [])
componentWillUnmount:
If you are used componentDidMount, So put componentWillUnmount next to it.
componentDidMount() {
window.addEventListener('mousemove', this.logMouseMove)
}
componentWillUnmount() {
window.removeEventListener('mousemove', this.logMouseMove)
}

The isMounted approach is an anti-pattern in most cases because it doesn't actually clean up/cancel anything, it just avoids changing state on unmounted components, but does nothing with pending asynchronous tasks. The React team recently removed the leak warning because users keep creating a lot of anti-patterns to hide the warning rather than fix its cause.
But writing cancellable code in plain JS can be really tricky. To fix this I made my own lib useAsyncEffect2 with custom hooks, built on top of a cancellable promise (c-promise2) for executing cancellable async code to reach its graceful cancellation. All async stages (promises), including deep ones, are cancellable. This means that the request here will be automatically aborted if its parent context is canceled. Of course, any other asynchronous operation can be used instead of a request.
useAsyncEffect Demo with plain useState usage (Live Demo):
import React, { useState } from "react";
import { useAsyncEffect } from "use-async-effect2";
import cpAxios from "cp-axios";
function TestComponent({url}) {
const [text, setText] = useState("");
const cancel = useAsyncEffect(
function* () {
setText("fetching...");
const json = (yield cpAxios(url)).data;
setText(`Success: ${JSON.stringify(json)}`);
},
[url]
);
return (
<div>
<div>{text}</div>
<button onClick={cancel}>
Cancel request
</button>
</div>
);
}
useAsyncEffect Demo with internal states usage (Live Demo):
import React from "react";
import { useAsyncEffect } from "use-async-effect2";
import cpAxios from "cp-axios";
function TestComponent({ url, timeout }) {
const [cancel, done, result, err] = useAsyncEffect(
function* () {
return (yield cpAxios(url).timeout(timeout)).data;
},
{ states: true, deps: [url] }
);
return (
<div>
{done ? (err ? err.toString() : JSON.stringify(result)) : "loading..."}
<button onClick={cancel} disabled={done}>
Cancel async effect (abort request)
</button>
</div>
);
}
Class component using decorators (Live demo)
import React, { Component } from "react";
import { ReactComponent } from "c-promise2";
import cpAxios from "cp-axios";
#ReactComponent
class TestComponent extends Component {
state = {
text: ""
};
*componentDidMount(scope) {
const { url, timeout } = this.props;
const response = yield cpAxios(url).timeout(timeout);
this.setState({ text: JSON.stringify(response.data, null, 2) });
}
render() {
return (<div>{this.state.text}</div>);
}
}
export default TestComponent;
More other examples:
Axios request with errors handling
Fetch weather by coords
Live search
Pause & Resume
Progress capturing

Edit: I just realized the warning is referencing a component called TextLayerInternal. That's likely where your bug is. The rest of this is still relevant, but it might not fix your problem.
1) Getting the instance of a component for this warning is tough. It looks like there is some discussion to improve this in React but there currently is no easy way to do it. The reason it hasn't been built yet, I suspect, is likely because components are expected to be written in such a way that setState after unmount isn't possible no matter what the state of the component is. The problem, as far as the React team is concerned, is always in the Component code and not the Component instance, which is why you get the Component Type name.
That answer might be unsatisfactory, but I think I can fix your problem.
2) Lodashes throttled function has a cancel method. Call cancel in componentWillUnmount and ditch the isComponentMounted. Canceling is more "idiomatically" React than introducing a new property.

UPDATE DO NOT USE MY ORIGINAL ANSWER AS IT DOES NOT WORK
This answer was based on the use of cancelable promises and a note in makecancelable which I migrated to use hooks. However, it appears it does not cancel a chain of async/await and even cancelable-promise does not support canceling of a chain of awaits
Doing a bit more research on this, it appears that some internal Google reasons prevented cancelable promises from coming into the standard.
Further more, there was some promise with Bluebird which introduces cancelable promises, but it does not work in Expo or at least I haven't seen an example of it working in Expo.
The accepted answer is the best. Since I use TypeScript I had adapted the code with a few modifications (I explicitly set the dependencies since the accepted answer's implicit dependencies appear to give a re-render loop on my app, added and use async/await rather than promise chain, pass a ref to the mounted object so that an async/await chain can be canceled earlier if needed)
/**
* This starts an async function and executes another function that performs
* React state changes if the component is still mounted after the async
* operation completes
* #template T
* #param {(mountedRef: React.MutableRefObject<boolean>) => Promise<T>} asyncFunction async function,
* it has a copy of the mounted ref so an await chain can be canceled earlier.
* #param {(asyncResult: T) => void} onSuccess this gets executed after async
* function is resolved and the component is still mounted
* #param {import("react").DependencyList} deps
*/
export function useAsyncSetEffect(asyncFunction, onSuccess, deps) {
const mountedRef = useRef(false);
useEffect(() => {
mountedRef.current = true;
(async () => {
const x = await asyncFunction(mountedRef);
if (mountedRef.current) {
onSuccess(x);
}
})();
return () => {
mountedRef.current = false;
};
}, deps);
}
Original answer
Since I have many different operations that are async, I use the cancelable-promise package to resolve this issue with minimal code changes.
Previous code:
useEffect(() =>
(async () => {
const bar = await fooAsync();
setSomeState(bar);
})(),
[]
);
New code:
import { cancelable } from "cancelable-promise";
...
useEffect(
() => {
const cancelablePromise = cancelable(async () => {
const bar = await fooAsync();
setSomeState(bar);
})
return () => cancelablePromise.cancel();
},
[]
);
You can alsowrpte it in a custom utility function like this
/**
* This wraps an async function in a cancelable promise
* #param {() => PromiseLike<void>} asyncFunction
* #param {React.DependencyList} deps
*/
export function useCancelableEffect(asyncFunction, deps) {
useEffect(() => {
const cancelablePromise = cancelable(asyncFunction());
return () => cancelablePromise.cancel();
}, deps);
}

In my case of a login-like screen, the fetch was done in a onClick handler of a parent component, who passed that handler down to the child, whom placed .catch and .finally on it.
In the .then case a redirect (and hence unmount) would happen as normal operation, and only in cases of fetch error would the child stay mounted on-screen.
My solution was moving the setState and all other code from the .finally to the .catch since the child is guaranteed to be mounted in the .catch case. And in the .then case nothing needed doing because of the guaranteed unmount.

Based on #ford04 answer, here is the same encapsulated in a method :
import React, { FC, useState, useEffect, DependencyList } from 'react';
export function useEffectAsync( effectAsyncFun : ( isMounted: () => boolean ) => unknown, deps?: DependencyList ) {
useEffect( () => {
let isMounted = true;
const _unused = effectAsyncFun( () => isMounted );
return () => { isMounted = false; };
}, deps );
}
Usage:
const MyComponent : FC<{}> = (props) => {
const [ asyncProp , setAsyncProp ] = useState( '' ) ;
useEffectAsync( async ( isMounted ) =>
{
const someAsyncProp = await ... ;
if ( isMounted() )
setAsyncProp( someAsyncProp ) ;
});
return <div> ... ;
} ;

Depending on how you open your webpage, you may not be causing a mounting. Such as using a <Link/> back to a page that was already mounted in the virtual DOM, so requiring data from a componentDidMount lifecycle is caught.

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 they 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 the Complete Code
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"
}
})

I solved this problem by providing all the params that are used in the useEffect hook
The code reported the bug:
useEffect(() => {
getDistrict({
geonameid: countryId,
subdistrict: level,
}).then((res) => {
......
});
}, [countryId]);
The code after fix:
useEffect(() => {
getDistrict({
geonameid: countryId,
subdistrict: level,
}).then((res) => {
......
});
}, [countryId,level]);
Can see that , problems solved after I provided all the params(including the level param) that supposed to pass through.

I had a similar problem and solved it :
I was automatically making the user logged-in by dispatching an action on redux
( placing authentication token on redux state )
and then I was trying to show a message with this.setState({succ_message: "...")
in my component.
Component was looking empty with the same error on console : "unmounted component".."memory leak" etc.
After I read Walter's answer up in this thread
I've noticed that in the Routing table of my application ,
my component's route wasn't valid if user is logged-in :
{!this.props.user.token &&
<div>
<Route path="/register/:type" exact component={MyComp} />
</div>
}
I made the Route visible whether the token exists or not.

In my case the issue was that the parent component was hidding the child because of a condition change in the child component.
So what I did was to change the condition so the child component was always shown.
What was happening:
const ParentComponent:FC = () => {
...
if (someCondition) {
return null;
}
return (
<>
Some cool text here
<ChildModalComponent message="this is a cool modal" />
</>
)
}
const ChildModalComponent: FC = () => {
...
const handleSubmit = () => {
setSomeCondition(true);
}
}
So after clicking submit the modal was automatically hidden becasue of the parent condition (someCondition).
How did I fix it?
I changed the place where the someCondition was checked in the Parent component, so the child component was always shown:
const ParentComponent:FC = () => {
...
return (
<>
{!someCondition && <>Some cool text here</>
<ChildModalComponent message="this is a cool modal" />
</>
)
}

I faced same warning, not it is fixed. To fix the issue, I removed the useRef() variable check in useEffect()
Earlier, the code was
const varRef = useRef();
useEffect(() => {
if (!varRef.current)
{
}
}, []);
Now, the code is
const varRef = useRef();
useEffect(() => {
//if (!varRef.current)
{
}
}, [])
Hope, it helps...

Inspired by the accepted answer by #ford04 I had even better approach dealing with it, instead of using useEffect inside useAsync create a new function that returns a callback for componentWillUnmount :
function asyncRequest(asyncRequest, onSuccess, onError, onComplete) {
let isMounted=true
asyncRequest().then((data => isMounted ? onSuccess(data):null)).catch(onError).finally(onComplete)
return () => {isMounted=false}
}
...
useEffect(()=>{
return asyncRequest(()=>someAsyncTask(arg), response=> {
setSomeState(response)
},onError, onComplete)
},[])

const handleClick = async (item: NavheadersType, index: number) => {
const newNavHeaders = [...navheaders];
if (item.url) {
await router.push(item.url); =>>>> line causing error (causing route to happen)
// router.push(item.url); =>>> coreect line
newNavHeaders.forEach((item) => (item.active = false));
newNavHeaders[index].active = true;
setnavheaders([...newNavHeaders]);
}
};

The simplest and most compact solution (with an explanation) is seen below as a one-liner solution.
useEffect(() => { return () => {}; }, []);
The useEffect() example above returns a callback function triggers React to finish its unmount portion of its life-cycle prior to updating state.
That very simplistic solution is all that is needed. In addition, it also works unlike the fictional syntax provided by #ford04 and #sfletche . By the way, the below code snippet from #ford04 is purely imaginary syntax (#sfletche , #vinod , #guneetgstar , and #Drew Cordano used the very same imaginary syntax).
data => {       <--- Fictional/Imaginary Syntax
someAsyncOperation().then(data => {
if (isMounted) setState(data); // add conditional check
})
All of my linters and all the linters of my entire team will not accept it and they report Uncaught SyntaxError: unexpected token: '=>'. I am surprised that no one caught the imaginary syntax. Would anyone who has participated in this question-thread, particularly among the up-voters, explain to me how they got the solutions to work for them?

Inspired by #ford04 answer I use this hook, which also takes callbacks for success, errors, finally and an abortFn:
export const useAsync = (
asyncFn,
onSuccess = false,
onError = false,
onFinally = false,
abortFn = false
) => {
useEffect(() => {
let isMounted = true;
const run = async () => {
try{
let data = await asyncFn()
if (isMounted && onSuccess) onSuccess(data)
} catch(error) {
if (isMounted && onError) onSuccess(error)
} finally {
if (isMounted && onFinally) onFinally()
}
}
run()
return () => {
if(abortFn) abortFn()
isMounted = false
};
}, [asyncFn, onSuccess])
}
If the asyncFn is doing some kind of fetch from back-end it often makes sense to abort it when the component is unmounted (not always though, sometimes if ie. you're loading some data into a store you might as well just want to finish it even if component is unmounted)

We Keep Coding

JavaScript is the programming language of the Web.

React: how to asynchronously and sequentially remove elements from array state? - javascript

If you want put cleanup in useEffect just do it. Activate useEffect when some boolean = true and with help onClick change it.

Related

Cannot retrieve current state inside async function in React.js

Calling setState in Axios async/await function [duplicate]

How to cleanup a async call in react component useEffect after unmount? [duplicate]

Preventing "not wrapped in act(...)" Jest warning when state update doesn't affect UI

Can't perform a React state update on an unmounted component

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