Description
I have component which shows data that get from server and display it on the table using the state, tableData and it must be set when Redux action is dispatched.
I've use action listener library which uses Redux middleware which consisting of 63 lines of code. redux-listeners-qkreltms.
For example when I register a function on analysisListIsReady({}).type which is ANALYSISLIST_IS_READY then when the action is dispatched, the function is called.
Issue
The issue is that react throws sometimes the error: Can't update react state... for setTableData so response data is ignored to be set. I want to figure it out when it happens.
I've assumed that it's because of unmounting of component, so I printed some logs, but none of logs are printed and also ComponentA is not disappeared.
It's not throing any error when I delete getAnalysisJsonPathApi and getResource, so I tried to reporuduce it, but failed... link
It's not throing any error when I delete listenMiddleware.addListener see: #2
#1
// ComponentA
const [tableData, setTableData] = useState([])
useEffect(() => {
return () => {
console.log("unmounted1")
}}, [])
useEffect(() => {
listenMiddleware.addListener(analysisListIsReady({}).type, (_) => {
try {
getAnalysisJsonPathApi().then((res) => {
//...
getResource(volumeUrl)
.then((data: any) => {
// ...
setTableData(data)
})
})
} catch (error) {
warn(error.message)
}
})
return () => {
console.log("unmounted2")
}
}, [])
export const getAnalysisJsonPathApi = () => {
return api
.post('/segment/volume')
.then(({ data }) => data)
export const getResource = async (src: string, isImage?: boolean): Promise<ArrayBuffer> =>
api
.get(src)
.then(({ data }) => data)
#2
// ComponentA
const [tableData, setTableData] = useState([])
useEffect(() => {
return () => {
console.log("unmounted1")
}}, [])
useEffect(() => {
if (steps.step2a) {
try {
getAnalysisJsonPathApi().then((res) => {
//...
getResource(volumeUrl)
.then((data: any) => {
// ...
setTableData(data)
})
})
} catch (error) {
warn(error.message)
}
}
return () => {
console.log("unmounted2")
}
}, [steps.step2a])
Well, its as you said:
because of unmounting of component
In your UseEffect() function, you need to check if the componenet is mounted or not, in other words, you need to do the componentDidMount & componentDidUpdate (if needed) logics:
const mounted = useRef();
useEffect(() => {
if (!mounted.current) {
// do componentDidMount logic
console.log('componentDidMount');
mounted.current = true;
} else {
// do componentDidUpdate logic
console.log('componentDidUpdate');
}
});
i didn't go to your question code detail, but my hint might help you, usually this error happens in fetchData function,
suppose you have a fetchData function like below:
fetchData(){
...
let call = await service.getData();
...
--->setState(newItems)//Here
}
so when api call end and state want to be updated, if component been unmounted, there is no state to be set,
you can use a bool variable and set it false when component will unmount:
let stillActive= true;
fetchData(){
active = true;
...
let call = await service.getData();
...
if(stillActive)
setState(newItems)//Here
}
}
componentWillUnmount(){
active = false;
}
I've found out it's because of redux-listeners-qkreltms, Redux middleware.
It keeps function when component is mounted into listener, but never changes its functions even component is unmounted.
middleware.addListener = (type, listener) => {
for (let i = 0; i < listeners.length; i += 1) {
if (listeners[i].type === type) {
return;
}
}
listeners.push(createListener(type, listener));
};
I have a variable that I want to keep track of and update its value between two classes. In one of my classes, I started using props like this with the variable isLoading in my Post class:
class Post extends React.Component {
constructor(props) {
super(props);
this.state = {
isLoading: false
};
}
post = () => {
this.props.uploadPost()
this.props.updatePhoto()
this.props.updateDescription('')
this.props.navigation.navigate('Home')
}
openLibrary = async () => {
const { status } = await Permissions.askAsync(Permissions.CAMERA_ROLL)
if (status === 'granted') {
const image = await ImagePicker.launchImageLibraryAsync()
if(!image.cancelled ){
this.setState({ isLoading: true });
const resize = await ImageManipulator.manipulateAsync(image.uri, [], { format: 'jpeg', compress: 0.1 })
const url = await this.props.uploadPhoto(resize.uri)
this.props.updatePhoto(url)
this.setState({ isLoading: false });
}
}
}
...
Now, I also have another class called Camera that I want to update this same variable. However, I'm not implementing a child like function where I call Post or Camera class in each other.
This is my code for Camera.
class CameraUpload extends React.Component {
state = {
type: Camera.Constants.Type.back,
};
snapPhoto = async () => {
const { status } = await Camera.requestPermissionsAsync();
if (status === 'granted') {
const image = await this.camera.takePictureAsync()
global.config.loading = true;
image ? this.props.navigation.navigate('Post') : null
if( !image.cancelled ){
const resize = await ImageManipulator.manipulateAsync(image.uri, [], { format: 'jpeg', compress: 0.1 })
const url = await this.props.uploadPhoto(resize.uri)
this.props.updatePhoto(url)
loading = false;
// url ? this.props.navigation.navigate('Post') : null
}
}
}
I tried using a global config variable but the variable's value was not getting updated between classes. Please let me know what the best way to go about solving this problem is. Thanks!
React Context
You can use the concept of "Context" in react. You may read about it here
https://reactjs.org/docs/context.html
Async Storage
Also you can use async storage if it suits your design
You can make one utility class:
import AsyncStorage from '#react-native-community/async-storage';
export async function storeData(key, value) {
try {
await AsyncStorage.setItem(key, value)
} catch (e) {
console.log("Error Storing in AsyncStorage stroing " + key + " in async Storage")
}
}
export async function getData(key) {
try {
const value = await AsyncStorage.getItem(key)
return (value == null || value == undefined) ? undefined : value
} catch (e) {
console.log("Error Reading in AsyncStorage stroing " + key + " in async Storage")
}
}
You can store and get data through key-value pairs.
// Firstly import it in your js
import * as asyncStorage from './AsyncStorage'
//For storingthe data:
await asyncStorage.storeData("key1", "value1");
// For getting the data:
await asyncStorage.getData("key1")
You can try global variable:
class post {
onpost(){
global.isLoading = true;
}
}
class cameraupload {
componentDidMount(){
global.isLoading = false;
}
}
Context is the way to go for small pieces of shared state, in my opinion.
Combined with hooks, it's very easy to access state and call functions from any child component.
Define your provider with any shared state and functions
import React, { createContext, useState } from 'react'
const Context = createContext()
const MySharedStateProvider = ({ children }) => {
const [myState, setMyState] = useState('hello')
const updateMyState = value => setMyState(value)
return (
<Context.Provider value={{ myState, updateMyState }}>
{children}
</Context.Provider>
)
}
export { MySharedStateProvider, Context as MySharedStateContext }
Create a hook for your Context, that can be used in any child component
import { useContext } from 'react'
import { MySharedStateContext } from './MySharedStateProvider.js'
export const useMySharedState = () => useContext(MySharedStateContext)
Wrap your components with the provider (I know it wouldn't look like this, it's just an example)
<MySharedStateProvider>
<Posts/>
<CameraUpload/>
</MySharedStateProvider>
Now in your Post or CameraUpload component, you use your hook to get the values
import { useMySharedState } from './MySharedStateHook.js'
const Post = () => {
const { myState, setMyState } = useMySharedState()
}
I'd like to change what a component shows depending on the URL parameter but at the same time to use the same component. When I execute my code componentDidMount is evoked for the first time, but after the second time, it doesn't work. As a result, I can't change what the component shows.
I'm using react.js.
Although I used componentDidUpdate instead of componentDidMount it caused an infinitive loop.
import React from "react";
import ReactMarkdown from "react-markdown";
import Contentful from "./Contentful";
import "./Article.css";
class ArticlesWithTag extends React.Component {
state = {
articleFromContentful: []
};
async componentDidMount() {
console.log("componentDidMount");
const { tag } = this.props.match.params;
//get article from contentful API
const contentful = new Contentful();
try {
const article = await contentful.getArtcleWithTags(
undefined,
"blogPost",
tag
);
this.setState({ articleFromContentful: article.items });
} catch (err) {
console.log("error");
console.log(err);
}
}
render() {
const bodyOfArticle = this.state.articleFromContentful.map(data => {
const returnTitle = () => {
return data.fields.title;
};
const returnPublishedDate = () => {
let date = data.fields.publishDate.substring(0, 10);
let replacedDate = date.replace("-", "/");
while (date !== replacedDate) {
date = date.replace("-", "/");
replacedDate = replacedDate.replace("-", "/");
}
return replacedDate;
};
const returnBody = () => {
return data.fields.body;
};
const returnTags = () => {
const tagList = data.fields.tags.map(data => {
const listContent = `#${data}`;
return <li>{listContent}</li>;
});
return tagList;
};
returnTags();
return (
<div className="article-container">
<div className="article-title">{returnTitle()}</div>
<p className="article-date">{returnPublishedDate()}</p>
<div className="article-body">
<ReactMarkdown source={returnBody()}></ReactMarkdown>
</div>
<div className="article-tags">
<ul>{returnTags()}</ul>
</div>
</div>
);
});
return <div className="article-outer">{bodyOfArticle}</div>;
}
}
export default ArticlesWithTag;
Ok componentDidMount is a lifecylce method that runs only when the component mounts
and componentDidUpdate runs everytime there's an update
You can set state in componentDidUpdate but it must be wrapped around some condition
In your case you can do something like this
async componentDidMount() {
console.log("componentDidMount");
const { tag } = this.props.match.params;
//get article from contentful API
const contentful = new Contentful();
try {
const article = await contentful.getArtcleWithTags(
undefined,
"blogPost",
tag
);
this.setState({ articleFromContentful: article.items });
} catch (err) {
console.log("error");
console.log(err);
}
}
and for further updates use compnentDidUpdate as
async componentDidUpdate(prevProps) {
const { tag } = this.props.match.params;
//get article from contentful API
const contentful = new Contentful();
if ( tag !== prevProps.match.params ) // if props have changed
{
try {
const article = await contentful.getArtcleWithTags(
undefined,
"blogPost",
tag
);
this.setState({ articleFromContentful: article.items });
} catch (err) {
console.log("error");
console.log(err);
}
}
}
Hope it helps
componentDidMount is called only when your component is mounted.
componentDidUpdate is called when the props has changed.
You should create a function from your componentDidMount logic and call it in componentDidUpdate only when tag has changed
componentDidMount() is only called when the component initially mounts onto the DOM. Re-renders caused by prop or state changes trigger componentDidUpdate(). As you mentioned, making state changes in this function causes infinite loops.
What you can do is use componentDidUpdate() and check if props have changed before deciding to update the state again. This should prevent your infinite loop situation.
I think the title says it all. The yellow warning is displayed every time I unmount a component that is still fetching.
Console
Warning: Can't call setState (or forceUpdate) on an unmounted component. This is a no-op, but ... To fix, cancel all subscriptions and asynchronous tasks in the componentWillUnmount method.
constructor(props){
super(props);
this.state = {
isLoading: true,
dataSource: [{
name: 'loading...',
id: 'loading',
}]
}
}
componentDidMount(){
return fetch('LINK HERE')
.then((response) => response.json())
.then((responseJson) => {
this.setState({
isLoading: false,
dataSource: responseJson,
}, function(){
});
})
.catch((error) =>{
console.error(error);
});
}
When you fire a Promise it might take a few seconds before it resolves and by that time user might have navigated to another place in your app. So when Promise resolves setState is executed on unmounted component and you get an error - just like in your case. This may also cause memory leaks.
That's why it is best to move some of your asynchronous logic out of components.
Otherwise, you will need to somehow cancel your Promise. Alternatively - as a last resort technique (it's an antipattern) - you can keep a variable to check whether the component is still mounted:
componentDidMount(){
this.mounted = true;
this.props.fetchData().then((response) => {
if(this.mounted) {
this.setState({ data: response })
}
})
}
componentWillUnmount(){
this.mounted = false;
}
I will stress that again - this is an antipattern but may be sufficient in your case (just like they did with Formik implementation).
A similar discussion on GitHub
EDIT:
This is probably how would I solve the same problem (having nothing but React) with Hooks:
OPTION A:
import React, { useState, useEffect } from "react";
export default function Page() {
const value = usePromise("https://something.com/api/");
return (
<p>{value ? value : "fetching data..."}</p>
);
}
function usePromise(url) {
const [value, setState] = useState(null);
useEffect(() => {
let isMounted = true; // track whether component is mounted
request.get(url)
.then(result => {
if (isMounted) {
setState(result);
}
});
return () => {
// clean up
isMounted = false;
};
}, []); // only on "didMount"
return value;
}
OPTION B: Alternatively with useRef which behaves like a static property of a class which means it doesn't make component rerender when it's value changes:
function usePromise2(url) {
const isMounted = React.useRef(true)
const [value, setState] = useState(null);
useEffect(() => {
return () => {
isMounted.current = false;
};
}, []);
useEffect(() => {
request.get(url)
.then(result => {
if (isMounted.current) {
setState(result);
}
});
}, []);
return value;
}
// or extract it to custom hook:
function useIsMounted() {
const isMounted = React.useRef(true)
useEffect(() => {
return () => {
isMounted.current = false;
};
}, []);
return isMounted; // returning "isMounted.current" wouldn't work because we would return unmutable primitive
}
Example: https://codesandbox.io/s/86n1wq2z8
The friendly people at React recommend wrapping your fetch calls/promises in a cancelable promise. While there is no recommendation in that documentation to keep the code separate from the class or function with the fetch, this seems advisable because other classes and functions are likely to need this functionality, code duplication is an anti-pattern, and regardless the lingering code should be disposed of or canceled in componentWillUnmount(). As per React, you can call cancel() on the wrapped promise in componentWillUnmount to avoid setting state on an unmounted component.
The provided code would look something like these code snippets if we use React as a guide:
const makeCancelable = (promise) => {
let hasCanceled_ = false;
const wrappedPromise = new Promise((resolve, reject) => {
promise.then(
val => hasCanceled_ ? reject({isCanceled: true}) : resolve(val),
error => hasCanceled_ ? reject({isCanceled: true}) : reject(error)
);
});
return {
promise: wrappedPromise,
cancel() {
hasCanceled_ = true;
},
};
};
const cancelablePromise = makeCancelable(fetch('LINK HERE'));
constructor(props){
super(props);
this.state = {
isLoading: true,
dataSource: [{
name: 'loading...',
id: 'loading',
}]
}
}
componentDidMount(){
cancelablePromise.
.then((response) => response.json())
.then((responseJson) => {
this.setState({
isLoading: false,
dataSource: responseJson,
}, () => {
});
})
.catch((error) =>{
console.error(error);
});
}
componentWillUnmount() {
cancelablePromise.cancel();
}
---- EDIT ----
I have found the given answer may not be quite correct by following the issue on GitHub. Here is one version that I use which works for my purposes:
export const makeCancelableFunction = (fn) => {
let hasCanceled = false;
return {
promise: (val) => new Promise((resolve, reject) => {
if (hasCanceled) {
fn = null;
} else {
fn(val);
resolve(val);
}
}),
cancel() {
hasCanceled = true;
}
};
};
The idea was to help the garbage collector free up memory by making the function or whatever you use null.
You can use AbortController to cancel a fetch request.
See also: https://www.npmjs.com/package/abortcontroller-polyfill
class FetchComponent extends React.Component{
state = { todos: [] };
controller = new AbortController();
componentDidMount(){
fetch('https://jsonplaceholder.typicode.com/todos',{
signal: this.controller.signal
})
.then(res => res.json())
.then(todos => this.setState({ todos }))
.catch(e => alert(e.message));
}
componentWillUnmount(){
this.controller.abort();
}
render(){
return null;
}
}
class App extends React.Component{
state = { fetch: true };
componentDidMount(){
this.setState({ fetch: false });
}
render(){
return this.state.fetch && <FetchComponent/>
}
}
ReactDOM.render(<App/>, document.getElementById('root'))
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="root"></div>
Since the post had been opened, an "abortable-fetch" has been added.
https://developers.google.com/web/updates/2017/09/abortable-fetch
(from the docs:)
The controller + signal manoeuvre
Meet the AbortController and AbortSignal:
const controller = new AbortController();
const signal = controller.signal;
The controller only has one method:
controller.abort();
When you do this, it notifies the signal:
signal.addEventListener('abort', () => {
// Logs true:
console.log(signal.aborted);
});
This API is provided by the DOM standard, and that's the entire API. It's deliberately generic so it can be used by other web standards and JavaScript libraries.
for example, here's how you'd make a fetch timeout after 5 seconds:
const controller = new AbortController();
const signal = controller.signal;
setTimeout(() => controller.abort(), 5000);
fetch(url, { signal }).then(response => {
return response.text();
}).then(text => {
console.log(text);
});
When I need to "cancel all subscriptions and asynchronous" I usually dispatch something to redux in componentWillUnmount to inform all other subscribers and send one more request about cancellation to server if necessary
The crux of this warning is that your component has a reference to it that is held by some outstanding callback/promise.
To avoid the antipattern of keeping your isMounted state around (which keeps your component alive) as was done in the second pattern, the react website suggests using an optional promise; however that code also appears to keep your object alive.
Instead, I've done it by using a closure with a nested bound function to setState.
Here's my constructor(typescript)…
constructor(props: any, context?: any) {
super(props, context);
let cancellable = {
// it's important that this is one level down, so we can drop the
// reference to the entire object by setting it to undefined.
setState: this.setState.bind(this)
};
this.componentDidMount = async () => {
let result = await fetch(…);
// ideally we'd like optional chaining
// cancellable.setState?.({ url: result || '' });
cancellable.setState && cancellable.setState({ url: result || '' });
}
this.componentWillUnmount = () => {
cancellable.setState = undefined; // drop all references.
}
}
I think if it is not necessary to inform server about cancellation - best approach is just to use async/await syntax (if it is available).
constructor(props){
super(props);
this.state = {
isLoading: true,
dataSource: [{
name: 'loading...',
id: 'loading',
}]
}
}
async componentDidMount() {
try {
const responseJson = await fetch('LINK HERE')
.then((response) => response.json());
this.setState({
isLoading: false,
dataSource: responseJson,
}
} catch {
console.error(error);
}
}
In addition to the cancellable promise hooks examples in the accepted solution, it can be handy to have a useAsyncCallback hook wrapping a request callback and returning a cancellable promise. The idea is the same, but with a hook working just like a regular useCallback. Here is an example of implementation:
function useAsyncCallback<T, U extends (...args: any[]) => Promise<T>>(callback: U, dependencies: any[]) {
const isMounted = useRef(true)
useEffect(() => {
return () => {
isMounted.current = false
}
}, [])
const cb = useCallback(callback, dependencies)
const cancellableCallback = useCallback(
(...args: any[]) =>
new Promise<T>((resolve, reject) => {
cb(...args).then(
value => (isMounted.current ? resolve(value) : reject({ isCanceled: true })),
error => (isMounted.current ? reject(error) : reject({ isCanceled: true }))
)
}),
[cb]
)
return cancellableCallback
}
one more alternative way is to wrap your async function in a wrapper that will handle the use case when the component unmounts
as we know function are also object in js so we can use them to update the closure values
const promesifiedFunction1 = (func) => {
return function promesify(...agrs){
let cancel = false;
promesify.abort = ()=>{
cancel = true;
}
return new Promise((resolve, reject)=>{
function callback(error, value){
if(cancel){
reject({cancel:true})
}
error ? reject(error) : resolve(value);
}
agrs.push(callback);
func.apply(this,agrs)
})
}
}
//here param func pass as callback should return a promise object
//example fetch browser API
//const fetchWithAbort = promesifiedFunction2(fetch)
//use it as fetchWithAbort('http://example.com/movies.json',{...options})
//later in componentWillUnmount fetchWithAbort.abort()
const promesifiedFunction2 = (func)=>{
return async function promesify(...agrs){
let cancel = false;
promesify.abort = ()=>{
cancel = true;
}
try {
const fulfilledValue = await func.apply(this,agrs);
if(cancel){
throw 'component un mounted'
}else{
return fulfilledValue;
}
}
catch (rejectedValue) {
return rejectedValue
}
}
}
then inside componentWillUnmount() simply call promesifiedFunction.abort()
this will update the cancel flag and run the reject function
Using CPromise package, you can cancel your promise chains, including nested ones. It supports AbortController and generators as a replacement for ECMA async functions. Using CPromise decorators, you can easily manage your async tasks, making them cancellable.
Decorators usage Live Demo :
import React from "react";
import { ReactComponent, timeout } from "c-promise2";
import cpFetch from "cp-fetch";
#ReactComponent
class TestComponent extends React.Component {
state = {
text: "fetching..."
};
#timeout(5000)
*componentDidMount() {
console.log("mounted");
const response = yield cpFetch(this.props.url);
this.setState({ text: `json: ${yield response.text()}` });
}
render() {
return <div>{this.state.text}</div>;
}
componentWillUnmount() {
console.log("unmounted");
}
}
All stages there are completely cancelable/abortable.
Here is an example of using it with React Live Demo
import React, { Component } from "react";
import {
CPromise,
CanceledError,
ReactComponent,
E_REASON_UNMOUNTED,
listen,
cancel
} from "c-promise2";
import cpAxios from "cp-axios";
#ReactComponent
class TestComponent extends Component {
state = {
text: ""
};
*componentDidMount(scope) {
console.log("mount");
scope.onCancel((err) => console.log(`Cancel: ${err}`));
yield CPromise.delay(3000);
}
#listen
*fetch() {
this.setState({ text: "fetching..." });
try {
const response = yield cpAxios(this.props.url).timeout(
this.props.timeout
);
this.setState({ text: JSON.stringify(response.data, null, 2) });
} catch (err) {
CanceledError.rethrow(err, E_REASON_UNMOUNTED);
this.setState({ text: err.toString() });
}
}
*componentWillUnmount() {
console.log("unmount");
}
render() {
return (
<div className="component">
<div className="caption">useAsyncEffect demo:</div>
<div>{this.state.text}</div>
<button
className="btn btn-success"
type="submit"
onClick={() => this.fetch(Math.round(Math.random() * 200))}
>
Fetch random character info
</button>
<button
className="btn btn-warning"
onClick={() => cancel.call(this, "oops!")}
>
Cancel request
</button>
</div>
);
}
}
Using Hooks and cancel method
import React, { useState } from "react";
import {
useAsyncEffect,
E_REASON_UNMOUNTED,
CanceledError
} from "use-async-effect2";
import cpAxios from "cp-axios";
export default function TestComponent(props) {
const [text, setText] = useState("");
const [id, setId] = useState(1);
const cancel = useAsyncEffect(
function* () {
setText("fetching...");
try {
const response = yield cpAxios(
`https://rickandmortyapi.com/api/character/${id}`
).timeout(props.timeout);
setText(JSON.stringify(response.data, null, 2));
} catch (err) {
CanceledError.rethrow(err, E_REASON_UNMOUNTED);
setText(err.toString());
}
},
[id]
);
return (
<div className="component">
<div className="caption">useAsyncEffect demo:</div>
<div>{text}</div>
<button
className="btn btn-success"
type="submit"
onClick={() => setId(Math.round(Math.random() * 200))}
>
Fetch random character info
</button>
<button className="btn btn-warning" onClick={cancel}>
Cancel request
</button>
</div>
);
}
Just four steps:
1.create instance of AbortController::const controller = new AbortController()
2.get signal:: const signal = controller.signal
3.pass signal to fetch parameter
4.controller abort anytime:: controller.abort();
const controller = new AbortController()
const signal = controller.signal
function beginFetching() {
var urlToFetch = "https://xyxabc.com/api/tt";
fetch(urlToFetch, {
method: 'get',
signal: signal,
})
.then(function(response) {
console.log('Fetch complete');
}).catch(function(err) {
console.error(` Err: ${err}`);
});
}
function abortFetching() {
controller.abort()
}
If you have a timeout clear them when component unmount.
useEffect(() => {
getReusableFlows(dispatch, selectedProject);
dispatch(fetchActionEvents());
const timer = setInterval(() => {
setRemaining(getRemainingTime());
}, 1000);
return () => {
clearInterval(timer);
};
}, []);
There are many great answers here and i decided to throw some in too. Creating your own version of useEffect to remove repetition is fairly simple:
import { useEffect } from 'react';
function useSafeEffect(fn, deps = null) {
useEffect(() => {
const state = { safe: true };
const cleanup = fn(state);
return () => {
state.safe = false;
cleanup?.();
};
}, deps);
}
Use it as a normal useEffect with state.safe being available for you in the callback that you pass:
useSafeEffect(({ safe }) => {
// some code
apiCall(args).then(result => {
if (!safe) return;
// updating the state
})
}, [dep1, dep2]);
This is a more general solution for async/await and promises.
I did this because my React callbacks were in between important async calls, so I couldn't cancel all the promises.
// TemporalFns.js
let storedFns = {};
const nothing = () => {};
export const temporalThen = (id, fn) => {
if(!storedFns[id])
storedFns[id] = {total:0}
let pos = storedFns[id].total++;
storedFns[id][pos] = fn;
return data => { const res = storedFns[id][pos](data); delete storedFns[id][pos]; return res; }
}
export const cleanTemporals = (id) => {
for(let i = 0; i<storedFns[id].total; i++) storedFns[id][i] = nothing;
}
Usage: (Obviously each instance should have different id)
const Test = ({id}) => {
const [data,setData] = useState('');
useEffect(() => {
someAsyncFunction().then(temporalThen(id, data => setData(data))
.then(otherImportantAsyncFunction).catch(...);
return () => { cleanTemporals(id); }
}, [])
return (<p id={id}>{data}</p>);
}
we can create a custom hook to wrap the fetch function like this:
//my-custom-fetch-hook.js
import {useEffect, useRef} from 'react'
function useFetch(){
const isMounted = useRef(true)
useEffect(() => {
isMounted.current = true //must set this in useEffect or your will get a error when the debugger refresh the page
return () => {isMounted.current = false}
}, [])
return (url, config) => {
return fetch(url, config).then((res) => {
if(!isMounted.current)
throw('component unmounted')
return res
})
}
}
export default useFetch
Then in our functional component:
import useFetch from './my-custom-fetch-hook.js'
function MyComponent(){
const fetch = useFetch()
...
fetch(<url>, <config>)
.then(res => res.json())
.then(json => { ...set your local state here})
.catch(err => {...do something})
}
I think I figured a way around it. The problem is not as much the fetching itself but the setState after the component is dismissed. So the solution was to set this.state.isMounted as false and then on componentWillMount change it to true, and in componentWillUnmount set to false again. Then just if(this.state.isMounted) the setState inside the fetch. Like so:
constructor(props){
super(props);
this.state = {
isMounted: false,
isLoading: true,
dataSource: [{
name: 'loading...',
id: 'loading',
}]
}
}
componentDidMount(){
this.setState({
isMounted: true,
})
return fetch('LINK HERE')
.then((response) => response.json())
.then((responseJson) => {
if(this.state.isMounted){
this.setState({
isLoading: false,
dataSource: responseJson,
}, function(){
});
}
})
.catch((error) =>{
console.error(error);
});
}
componentWillUnmount() {
this.setState({
isMounted: false,
})
}