This question already has answers here:
State not updating when using React state hook within setInterval
(14 answers)
Closed 5 months ago.
I'm working on building a file upload portal in React that allows for multiple concurrent uploads, using an amalgamation of some preexisting code and new code that I'm writing myself. The code base is pretty complex, so I will explain what's happening at a high level, illustrate the problem, and then provide a toy example to simulate what's happening in CodeSandbox.
The top level component has a files state variable from useState, which is an object that contains sub objects with information regarding each file that the user is currently uploading, that is being mapped across in the JSX and returning UI elements for each. Think:
const uploadData = {
1: {
id: 1,
name: "File 1",
progress: 0
},
2: {
id: 2,
name: "File 2",
progress: 0
}
};
const [files, setFiles] = useState(uploadData);
const progressElements = Object.values(files).map((file) => (
<Progress key={file.id} value={file.progress} />
))
When an upload is initiated, existing code dictates that a callback is provided from the top level that receives an updated progress value for a given upload, and then sets that into state in files for the corresponding upload. This works perfectly fine when there is only one active upload, but as soon as a second file is added, the fact that the same files state object is being concurrently updated in multiple places at once bugs out the UI and causes the rendered JSX to be inaccurate. What is the correct way to handle concurrent updates to the same state at once?
Below is a super simplified (and hastily written, my apologies) sandbox as a toy example of what's going on. It's obviously not an exact replica of what's happening in the actual code, but it gets the general idea across. You can see that, with one upload going, the UI updates fine. But when additional uploads are added, any updates to the first overwrite the existence of the new upload in state and thus break the UI.
https://codesandbox.io/s/elastic-wozniak-yvbfo6?file=/src/App.js:133-297
const { useState, useEffect } = React;
const App = () => {
const uploadData = {
1: {
id: 1,
name: "File 1",
progress: 0
}
};
const [files, setFiles] = useState(uploadData);
const [uploading, setUploading] = useState(false);
const updateProgress = (uploadId, progress) => {
setFiles({
...files,
[uploadId]: {
...files[uploadId],
progress
}
});
};
const filesArray = Object.values(files);
const addNewFile = () => {
const lastUpload = files[filesArray.length];
const newId = lastUpload.id + 1;
setFiles({
...files,
[newId]: {
id: newId,
name: 'File ' + newId,
progress: 0
}
});
};
return (
<div className="App">
{filesArray.map((file) => (
<UploadStatus
key={file.id}
uploading={uploading}
setUploading={setUploading}
file={file}
updateProgress={updateProgress}
/>
))}
<button
onClick={
uploading ? () => setUploading(false) : () => setUploading(true)
}
>
{uploading ? "Cancel Upload" : "Start Upload"}
</button>
{uploading && <button onClick={addNewFile}>Add New File</button>}
</div>
);
}
const UploadStatus = ({
file,
updateProgress,
uploading,
setUploading
}) => {
useEffect(() => {
if (!uploading) return;
let calls = 0;
const interval = setInterval(() => {
calls++;
updateProgress(file.id, calls * 10);
}, 1000);
if (calls === 10) {
clearInterval(interval);
setUploading(false);
}
return () => clearInterval(interval);
}, [uploading]);
return (
<div key={file.id}>
<p>{file.name}</p>
<progress value={file.progress} max="100" />
</div>
);
}
ReactDOM.render(<App />, document.getElementById("root"));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/18.0.0/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/18.0.0/umd/react-dom.production.min.js"></script>
<body>
<div id="root"></div>
</body>
Any help or thoughts would be greatly appreciated. Thanks!
Based on what is inside your codesandbox - the issue is just with closures and missing items in dependency array of useEffect. I do understand why you want to have only the things you described in depsArray of useEffect - but if you dont provide all the things there - you will get an issue with closure and you will be calling the old function or refering old variable, what is happening in your codesandbox. Consider wrapping everything that is passed to the hooks or child components with useMemo, useCallback and other memoizing functions react provide and include everything that is needed in depsArray. There is a workaround with useRef hook to hold a reference to the specific function you want to call + useEffect with the only purpose to update this useRef variable.
So rough fix 1:
import { useEffect, useRef } from "react";
export default function UploadStatus({
file,
updateProgress,
uploading,
setUploading
}) {
const updateProgressRef = useRef(updateProgress);
const setUploadingRef = useRef(setUploading);
useEffect(() => {
updateProgressRef.current = updateProgress;
}, [updateProgress]);
useEffect(() => {
setUploadingRef.current = setUploading;
}, [setUploading]);
useEffect(() => {
if (!uploading) return;
let calls = 0;
const interval = setInterval(() => {
calls++;
updateProgressRef.current(file.id, calls * 10);
if (calls === 10) {
clearInterval(interval);
setUploadingRef.current(false);
}
}, 1000);
return () => clearInterval(interval);
}, [file.id, uploading]);
return (
<div key={file.id}>
<p>{file.name}</p>
<progress value={file.progress} max="100" />
</div>
);
}
You will have to fix some logic here due to when any of the Uploadings is done - all the rest uploading will "stop" due to uploading and setUploading parameters.
What can simplify the fixing process is to modify addNewFile and updateProgress so they will not rely on closure captured files. setXXX functions from useState can recieve either the new value as a parameter, either a callback currentValue => newValue. So you can use callback one:
So rough fix 2:
const updateProgress = (uploadId, progress) => {
setFiles((files) => ({
...files,
[uploadId]: {
...files[uploadId],
progress
}
}));
};
const addNewFile = () => {
const lastUpload = files[filesArray.length];
const newId = lastUpload.id + 1;
setFiles((files) => ({
...files,
[newId]: {
id: newId,
name: `File ${newId}`,
progress: 0
}
}));
};
This fix will actually work better but still, wirings of states and components and depsArray should be fixed more precisiolly.
Hope that helps you to get the basic idea of what is going on and in which direction to dig with your issues.
I am getting this warning in react:
index.js:1 Warning: Cannot update a component (`ConnectFunction`)
while rendering a different component (`Register`). To locate the
bad setState() call inside `Register`
I went to the locations indicated in the stack trace and removed all setstates but the warning still persists. Is it possible this could occur from redux dispatch?
my code:
register.js
class Register extends Component {
render() {
if( this.props.registerStatus === SUCCESS) {
// Reset register status to allow return to register page
this.props.dispatch( resetRegisterStatus()) # THIS IS THE LINE THAT CAUSES THE ERROR ACCORDING TO THE STACK TRACE
return <Redirect push to = {HOME}/>
}
return (
<div style = {{paddingTop: "180px", background: 'radial-gradient(circle, rgba(106,103,103,1) 0%, rgba(36,36,36,1) 100%)', height: "100vh"}}>
<RegistrationForm/>
</div>
);
}
}
function mapStateToProps( state ) {
return {
registerStatus: state.userReducer.registerStatus
}
}
export default connect ( mapStateToProps ) ( Register );
function which triggers the warning in my registerForm component called by register.js
handleSubmit = async () => {
if( this.isValidForm() ) {
const details = {
"username": this.state.username,
"password": this.state.password,
"email": this.state.email,
"clearance": this.state.clearance
}
await this.props.dispatch( register(details) )
if( this.props.registerStatus !== SUCCESS && this.mounted ) {
this.setState( {errorMsg: this.props.registerError})
this.handleShowError()
}
}
else {
if( this.mounted ) {
this.setState( {errorMsg: "Error - registration credentials are invalid!"} )
this.handleShowError()
}
}
}
Stacktrace:
This warning was introduced since React V16.3.0.
If you are using functional components you could wrap the setState call into useEffect.
Code that does not work:
const HomePage = (props) => {
props.setAuthenticated(true);
const handleChange = (e) => {
props.setSearchTerm(e.target.value.toLowerCase());
};
return (
<div key={props.restInfo.storeId} className="container-fluid">
<ProductList searchResults={props.searchResults} />
</div>
);
};
Now you can change it to:
const HomePage = (props) => {
// trigger on component mount
useEffect(() => {
props.setAuthenticated(true);
}, []);
const handleChange = (e) => {
props.setSearchTerm(e.target.value.toLowerCase());
};
return (
<div key={props.restInfo.storeId} className="container-fluid">
<ProductList searchResults={props.searchResults} />
</div>
);
};
I just had this issue and it took me a bit of digging around before I realised what I'd done wrong – I just wasn't paying attention to how I was writing my functional component.
I was doing this:
const LiveMatches = (props: LiveMatchesProps) => {
const {
dateMatches,
draftingConfig,
sportId,
getDateMatches,
} = props;
if (!dateMatches) {
const date = new Date();
getDateMatches({ sportId, date });
};
return (<div>{component stuff here..}</div>);
};
I had just forgotten to use useEffect before dispatching my redux call of getDateMatches()
So it should have been:
const LiveMatches = (props: LiveMatchesProps) => {
const {
dateMatches,
draftingConfig,
sportId,
getDateMatches,
} = props;
useEffect(() => {
if (!dateMatches) {
const date = new Date();
getDateMatches({ sportId, date });
}
}, [dateMatches, getDateMatches, sportId]);
return (<div>{component stuff here..}</div>);
};
please read the error message thoroughly, mine was pointing to SignIn Component that had a bad setState. which when i examined, I had an onpress that was not an Arrow function.
it was like this:
onPress={navigation.navigate("Home", { screen: "HomeScreen" })}
I changed it to this:
onPress={() => navigation.navigate("Home", { screen: "HomeScreen" }) }
My error message was:
Warning: Cannot update a component
(ForwardRef(BaseNavigationContainer)) while rendering a different
component (SignIn). To locate the bad setState() call inside
SignIn, follow the stack trace as described in
https://reactjs.org/link/setstate-in-render
in SignIn (at SignInScreen.tsx:20)
I fixed this issue by removing the dispatch from the register components render method to the componentwillunmount method. This is because I wanted this logic to occur right before redirecting to the login page. In general it's best practice to put all your logic outside the render method so my code was just poorly written before. Hope this helps anyone else in future :)
My refactored register component:
class Register extends Component {
componentWillUnmount() {
// Reset register status to allow return to register page
if ( this.props.registerStatus !== "" ) this.props.dispatch( resetRegisterStatus() )
}
render() {
if( this.props.registerStatus === SUCCESS ) {
return <Redirect push to = {LOGIN}/>
}
return (
<div style = {{paddingTop: "180px", background: 'radial-gradient(circle, rgba(106,103,103,1) 0%, rgba(36,36,36,1) 100%)', height: "100vh"}}>
<RegistrationForm/>
</div>
);
}
}
I think that this is important.
It's from this post that #Red-Baron pointed out:
#machineghost : I think you're misunderstanding what the message is warning about.
There's nothing wrong with passing callbacks to children that update state in parents. That's always been fine.
The problem is when one component queues an update in another component, while the first component is rendering.
In other words, don't do this:
function SomeChildComponent(props) {
props.updateSomething();
return <div />
}
But this is fine:
function SomeChildComponent(props) {
// or make a callback click handler and call it in there
return <button onClick={props.updateSomething}>Click Me</button>
}
And, as Dan has pointed out various times, queuing an update in the same component while rendering is fine too:
function SomeChildComponent(props) {
const [number, setNumber] = useState(0);
if(props.someValue > 10 && number < 5) {
// queue an update while rendering, equivalent to getDerivedStateFromProps
setNumber(42);
}
return <div>{number}</div>
}
If useEffect cannot be used in your case or if the error is NOT because of Redux
I used setTimeout to redirect one of the two useState variables to the callback queue.
I have one parent and one child component with useState variable in each of them. The solution is to wrap useState variable using setTimeout:
setTimeout(() => SetFilterData(data), 0);
Example below
Parent Component
import ExpenseFilter from '../ExpensesFilter'
function ExpensesView(props) {
const [filterData, SetFilterData] = useState('')
const GetFilterData = (data) => {
// SetFilterData(data);
//*****WRAP useState VARIABLE INSIDE setTimeout WITH 0 TIME AS BELOW.*****
setTimeout(() => SetFilterData(data), 0);
}
const filteredArray = props.expense.filter(expenseFiltered =>
expenseFiltered.dateSpent.getFullYear().toString() === filterData);
return (
<Window>
<div>
<ExpenseFilter FilterYear = {GetFilterData}></ExpenseFilter>
Child Component
const ExpensesFilter = (props) => {
const [filterYear, SetFilterYear] = useState('2022')
const FilterYearListener = (event) => {
event.preventDefault()
SetFilterYear(event.target.value)
}
props.FilterYear(filterYear)
return (
Using React and Material UI (MUI)
I changed my code from:
<IconButton onClick={setOpenDeleteDialog(false)}>
<Close />
</IconButton>
To:
<IconButton onClick={() => setOpenDeleteDialog(false)}>
<Close />
</IconButton>
Simple fix
If you use React Navigation and you are using the setParams or setOptions you must put these inside method componentDidMount() of class components or in useEffects() hook of functional components.
Minimal reproducing example
I was a bit confused as to what exactly triggers the problem, having a minimal immediately runnable example helped me grasp it a little better:
index.html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<script src="https://unpkg.com/react#17/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom#17/umd/react-dom.development.js"></script>
<script src="https://unpkg.com/#babel/standalone#7.14.7/babel.min.js"></script>
</head>
<body>
<div id="root"></div>
<script type="text/babel">
function NotMain(props) {
props.setN(1)
return <div>NotMain</div>
}
function Main(props) {
const [n, setN] = React.useState(0)
return <>
<NotMain setN={setN} />
<div>Main {n}</div>
</>
}
ReactDOM.render(
<Main/>,
document.getElementById('root')
);
</script>
</body>
</html>
fails with error:
react-dom.development.js:61 Warning: Cannot update a component (`Main`) while rendering a different component (`NotMain`). To locate the bad setState() call inside `NotMain`, follow the stack trace as described in https://reactjs.org/link/setstate-in-render
followed by a stack trace:
at NotMain (<anonymous>:16:9)
at Main (<anonymous>:21:31)
Presumably 16:9 would be the exact line where props.setN(1) is being called from, but the line numbers are a bit messed up because of the Babel JSX translation.
The solution like many other answers said is to do instead:
function NotMain(props) {
React.useEffect(() => { props.setN(1) }, [])
return <div>NotMain</div>
}
Intuitively, I think that the general idea of why this error happens is that:
You are not supposed to updat state from render methods, otherwise it could lead to different results depending on internal the ordering of how React renders things.
and when using functional components, the way to do that is to use hooks. In our case, useEffect will run after rendering is done, so we are fine doing that from there.
When using classes this becomes slightly more clear and had been asked for example at:
Calling setState in render is not avoidable
Calling setState() in React from render method
When using functional components however, things are conceptually a bit more mixed, as the component function is both the render, and the code that sets up the callbacks.
I was facing same issue, The fix worked for me was if u are doing
setParams/setOptions
outside of useEffect then this issue is occurring. So try to do such things inside useEffect. It'll work like charm
TL;DR;
For my case, what I did to fix the warning was to change from useState to useRef
react_devtools_backend.js:2574 Warning: Cannot update a component (`Index`) while rendering a different component (`Router.Consumer`). To locate the bad setState() call inside `Router.Consumer`, follow the stack trace as described in https://reactjs.org/link/setstate-in-render
at Route (http://localhost:3000/main.bundle.js:126692:29)
at Index (http://localhost:3000/main.bundle.js:144246:25)
at Switch (http://localhost:3000/main.bundle.js:126894:29)
at Suspense
at App
at AuthProvider (http://localhost:3000/main.bundle.js:144525:23)
at ErrorBoundary (http://localhost:3000/main.bundle.js:21030:87)
at Router (http://localhost:3000/main.bundle.js:126327:30)
at BrowserRouter (http://localhost:3000/main.bundle.js:125948:35)
at QueryClientProvider (http://localhost:3000/main.bundle.js:124450:21)
The full code for the context of what I did (changed from the lines with // OLD: to the line above them). However this doesn't matter, just try changing from useState to useRef!!
import { HOME_PATH, LOGIN_PATH } from '#/constants';
import { NotFoundComponent } from '#/routes';
import React from 'react';
import { Redirect, Route, RouteProps } from 'react-router-dom';
import { useAccess } from '#/access';
import { useAuthContext } from '#/contexts/AuthContext';
import { AccessLevel } from '#/models';
type Props = RouteProps & {
component: Exclude<RouteProps['component'], undefined>;
requireAccess: AccessLevel | undefined;
};
export const Index: React.FC<Props> = (props) => {
const { component: Component, requireAccess, ...rest } = props;
const { isLoading, isAuth } = useAuthContext();
const access = useAccess();
const mounted = React.useRef(false);
// OLD: const [mounted, setMounted] = React.useState(false);
return (
<Route
{...rest}
render={(props) => {
// If in indentifying authentication state as the page initially loads, render a blank page
if (!mounted.current && isLoading) return null;
// OLD: if (!mounted && isLoading) return null;
// 1. Check Authentication is one step
if (!isAuth && window.location.pathname !== LOGIN_PATH)
return <Redirect to={LOGIN_PATH} />;
if (isAuth && window.location.pathname === LOGIN_PATH)
return <Redirect to={HOME_PATH} />;
// 2. Authorization is another
if (requireAccess && !access[requireAccess])
return <NotFoundComponent />;
mounted.current = true;
// OLD: setMounted(true);
return <Component {...props} />;
}}
/>
);
};
export default Index;
My example.
Code with that error:
<Form
initialValues={{ ...kgFormValues, dataflow: dataflows.length > 0 ? dataflows[0].df_tpl_key : "" }}
onSubmit={() => {}}
render={({values, dirtyFields }: any) => {
const kgFormValuesUpdated = {
proj_key: projectKey,
name: values.name,
description: values.description,
public: values.public,
dataflow: values.dataflow,
flavours: flavoursSelected,
skipOCR: values.skipOCR
};
if (!_.isEqual(kgFormValues, kgFormValuesUpdated)) {
setNewKgFormValues(kgFormValuesUpdated);
}
Working Code:
<Form
initialValues={{ ...kgFormValues, dataflow: dataflows.length > 0 ? dataflows[0].df_tpl_key : "" }}
onSubmit={() => {}}
render={({ values, dirtyFields }: any) => {
useEffect(() => {
const kgFormValuesUpdated = {
proj_key: projectKey,
name: values.name,
description: values.description,
public: values.public,
dataflow: values.dataflow,
flavours: flavoursSelected,
skipOCR: values.skipOCR
};
if (!_.isEqual(kgFormValues, kgFormValuesUpdated)) {
setNewKgFormValues(kgFormValuesUpdated);
}
}, [values]);
return (
I had the same problem. I was setting some state that was storing a function like so:
// my state definition
const [onConfirm, setOnConfirm] = useState<() => void>();
// then I used this piece of code to update the state
function show(onConfirm: () => void) {
setOnConfirm(onConfirm);
}
The problem was from setOnConfirm. In React, setState can take the new value OR a function that returns the new value. In this case React wanted to get the new state from calling onConfirm which is not correct.
changing to this resolved my issue:
setOnConfirm(() => onConfirm);
I was able to solve this after coming across a similar question in GitHub which led me to this comment showing how to pinpoint the exact line within your file causing the error. I wasn't aware that the stack trace was there. Hopefully this helps someone!
See below for my fix. I simply converted the function to use callback.
Old code
function TopMenuItems() {
const dispatch = useDispatch();
function mountProjectListToReduxStore(projects) {
const projectDropdown = projects.map((project) => ({
id: project.id,
name: project.name,
organizationId: project.organizationId,
createdOn: project.createdOn,
lastModifiedOn: project.lastModifiedOn,
isComplete: project.isComplete,
}));
projectDropdown.sort((a, b) => a.name.localeCompare(b.name));
dispatch(loadProjectsList(projectDropdown));
dispatch(setCurrentOrganizationId(projectDropdown[0].organizationId));
}
};
New code
function TopMenuItems() {
const dispatch = useDispatch();
const mountProjectListToReduxStore = useCallback((projects) => {
const projectDropdown = projects.map((project) => ({
id: project.id,
name: project.name,
organizationId: project.organizationId,
createdOn: project.createdOn,
lastModifiedOn: project.lastModifiedOn,
isComplete: project.isComplete,
}));
projectDropdown.sort((a, b) => a.name.localeCompare(b.name));
dispatch(loadProjectsList(projectDropdown));
dispatch(setCurrentOrganizationId(projectDropdown[0].organizationId));
}, [dispatch]);
};
My case was using setState callback, instead of setState + useEffect
BAD ❌
const closePopover = useCallback(
() =>
setOpen((prevOpen) => {
prevOpen && onOpenChange(false);
return false;
}),
[onOpenChange]
);
GOOD ✅
const closePopover = useCallback(() => setOpen(false), []);
useEffect(() => onOpenChange(isOpen), [isOpen, onOpenChange]);
I got this when I was foolishly invoking a function that called dispatch instead of passing a reference to it for onClick on a button.
const quantityChangeHandler = (direction) => {
dispatch(cartActions.changeItemQuantity({title, quantityChange: direction}));
}
...
<button onClick={() => quantityChangeHandler(-1)}>-</button>
<button onClick={() => quantityChangeHandler(1)}>+</button>
Initially, I was directly calling without the fat arrow wrapper.
Cannot update a component while rendering a different component warning
I have the same problem but when I dispatch an action inside a component rendered. You should dispatch the action inside useEffect hook to fix that problem
//dispatch action to inform user that 'Marked days already have hours!'
React.useEffect(() => {
if (btn_class == 'redButton') {
dispatch({ type: ActionType.ADD_NOTIFICATION, payload: 'Marked days already have hours!' });
} else {
dispatch({ type: ActionType.ADD_NOTIFICATION, payload: '' });
}
}, [btn_class, dispatch]);
also use union type for btn-class variable
*`
type ButtonState = 'btnAddDay' | 'redButton' | 'btnAddDayBlue' | 'btnAddDayGreen';
`*
Using some of the answers above, i got rid of the error with the following:
from
if (value === "newest") {
dispatch(sortArticlesNewest());
} else {
dispatch(sortArticlesOldest());
}
this code was on my component top-level
to
const SelectSorting = () => {
const dispatch = useAppDispatch();
const {value, onChange} = useSelect();
useEffect(() => {
if (value === "newest") {
dispatch(sortArticlesNewest());
} else {
dispatch(sortArticlesOldest());
}
}, [dispatch, value]);
I'm trying to send a delete request to delete an item from an API.
The API request is fine when clicking on the button. But Item get's deleted only after refreshing the browser!
I'm not too sure if I should add any parameter to SetHamsterDeleted for it to work?
This is what my code looks like.
import React, {useState} from "react";
const Hamster = (props) => {
const [hamsterDeleted, setHamsterDeleted] = useState("")
async function deleteHamster(id) {
const response = await fetch(`/hamsters/${id}`, { method: "DELETE" });
setHamsterDeleted()
}
return (
<div>
<p className={props.hamster ? "" : "hide"}>
{hamsterDeleted}
</p>
<button onClick={() => deleteHamster(props.hamster.id)}>Delete</button>
<h2>{props.hamster.name}</h2>
<p>Ålder:{props.hamster.age}</p>
<p>Favorit mat:{props.hamster.favFood}</p>
<p>Matcher:{props.hamster.games}</p>
<img src={'./img/' + props.hamster.imgName} alt="hamster"/>
</div>
)
};
export default Hamster;
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>
Imagine you have a parent component (say HamstersList) that returns/renders list of these Hamster components - it would be preferable to declare that deleteHamster method in it, so it could either: a) pass some prop like hidden into every Hamster or b) refetch list of all Hamsters from the API after one got "deleted" c) remove "deleted" hamster from an array that was stored locally in that parent List component.
But since you are trying to archive this inside of Hamster itself, few changes might help you:
change state line to const [hamsterDeleted, setHamsterDeleted] = useState(false)
call setHamsterDeleted(true) inside of deleteHamster method after awaited fetch.
a small tweak of "conditional rendering" inside of return, to actually render nothing when current Hamster has hamsterDeleted set to true:
return hamsterDeleted ? null : (<div>*all your hamster's content here*</div>)
What do you want to do in the case the hamster is deleted? If you don't want to return anything, you can just return null.
I'm not too sure if I should add any parameter to SetHamsterDeleted for it to work?
Yes, I'd make this a boolean instead. Here's an example:
import React, { useState } from "react";
const Hamster = (props) => {
const [hamsterDeleted, setHamsterDeleted] = useState(false);
async function deleteHamster(id) {
const response = await fetch(`/hamsters/${id}`, { method: "DELETE" });
setHamsterDeleted(true);
}
if (hamsterDeleted) return null;
return (
<div>
<p className={props.hamster ? "" : "hide"}>
{hamsterDeleted}
</p>
<button onClick={() => deleteHamster(props.hamster.id)}>Delete</button>
<h2>{props.hamster.name}</h2>
<p>Ålder:{props.hamster.age}</p>
<p>Favorit mat:{props.hamster.favFood}</p>
<p>Matcher:{props.hamster.games}</p>
<img src={'./img/' + props.hamster.imgName} alt="hamster"/>
</div>
);
};
HOWEVER! Having each individual hamster keep track of its deleted state doesn't sound right (of course I don't know all your requirements but it seems odd). I'm guessing that you've got a parent component which is fetching all the hamsters - that would be a better place to keep track of what has been deleted, and what hasn't. That way, if the hamster is deleted, you could just not render that hamster. Something more like this:
const Hamsters = () => {
const [hamsers, setHamsters] = useState([]);
// Load the hamsters when the component loads
useEffect(() => {
const loadHamsters = async () => {
const { data } = await fetch(`/hamsters`, { method: "GET" });
setHamsters(data);
}
loadHamsters();
}, []);
// Shared handler to delete a hamster
const handleDelete = async (id) => {
await fetch(`/hamsters/${id}`, { method: "DELETE" });
setHamsters(prev => prev.filter(h => h.id !== id));
}
return (
<>
{hamsters.map(hamster => (
<Hamster
key={hamster.id}
hamster={hamster}
onDelete={handleDelete}
/>
))}
</>
);
}
Now you can just make the Hamster component a presentational component that only cares about rendering a hamster, eg:
const Hamster = ({ hamster, onDelete }) => {
const handleDelete = () => onDelete(hamster.id);
return (
<div>
<button onClick={handleDelete}>Delete</button>
<h2>{hamster.name}</h2>
<p>Ålder:{hamster.age}</p>
<p>Favorit mat:{hamster.favFood}</p>
<p>Matcher:{hamster.games}</p>
<img src={'./img/' + hamster.imgName} alt="hamster"/>
</div>
);
};
I have a page wherein there are Listings.
A user can check items from this list.
Whenever the user checks something it gets added to a globally declared Set(each item's unique ID is added into this set). The ID's in this set need to be accessed by a seperate Component(lets call it PROCESS_COMPONENT) which processes the particular Listings whose ID's are present in the set.
My Listings code roughly looks like:
import React from "react";
import { CheckBox, PROCESS_COMPONENT } from "./Process.jsx";
const ListItem = ({lItem}) => {
return (
<>
//name,image,info,etc.
<CheckBox lId={lItem.id}/>
</>
)
};
function Listings() {
// some declarations blah blah..
return (
<>
<PROCESS_COMPONENT /> // Its a sticky window that shows up on top of the Listings.
//..some divs and headings
dataArray.map(item => { return <ListItem lItem={item} /> }) // Generates the list also containing the checkboxes
</>
)
}
And the Checkbox and the PROCESS_COMPONENT functionality is present in a seperate file(Process.jsx).
It looks roughly like:
import React, { useEffect, useState } from "react";
let ProcessSet = new Set(); // The globally declared set.
const CheckBox = ({lID}) => {
const [isTicked, setTicked] = useState(false);
const onTick = () => setTicked(!isTicked);
useEffect( () => {
if(isTicked) {
ProcessSet.add(lID);
}
else {
ProcessSet.delete(lID);
}
console.log(ProcessSet); // Checking for changes in set.
}, [isTicked]);
return (
<div onClick={onTick}>
//some content
</div>
)
}
const PROCESS_COMPONENT = () => {
const [len, setLen] = useState(ProcessSet.size);
useEffect( () => {
setLen(ProcessSet.size);
}, [ProcessSet]); // This change is never being picked up.
return (
<div>
<h6> {len} items checked </h6>
</div>
)
}
export { CheckBox, PROCESS_COMPONENT };
The Set itself does get the correct ID values from the Checkbox. But the PROCESS_COMPONENT does not seem to be picking up the changes in the Set and len shows 0(initial size of the set).
I am pretty new to react. However any help is appreciated.
Edit:
Based on #jdkramhoft
's answer I made the set into a state variable in Listings function.
const ListItem = ({lItem,set,setPSet}) => {
//...
<CheckBox lID={lItem.id} pset={set} setPSet={setPSet} />
)
}
function Listings() {
const [processSet, setPSet] = useState(new Set());
//....
<PROCESS_COMPONENT set={processSet} />
dataArray.map(item => {
return <ListItem lItem={item} set={processSet} setPSet={setPSet} />
})
}
And corresponding changes in Process.jsx
const CheckBox = ({lID,pset,setPSet}) => {
//...
if (isTicked) {
setPSet(pset.add(lID));
}
else {
setPSet(pset.delete(lID));
}
//...
}
const PROCESS_COMPONENT = ({set}) => {
//...
setLen(set.size);
//...
}
Now whenever I click the check box I get an error:
TypeError: pset.add is not a function. (In 'pset.add(lID)', 'pset.add' is undefined)
Similar error occurs for the delete function as well.
First of all, the set should be a react state const [mySet, setMySet] = useState(new Set()); if you want react to properly re-render with detected changes. If you need the set to be available to multiple components you can pass it to them with props or use a context.
Secondly, React checks if dependencies like [ProcessSet] has been changed with something like ===. Even though the items in the set are different, no change is detected because the object is the same and there is no re-render.
Update:
The setState portion of [state, setState] = useState([]); is not intended to mutate the previous state - only to provide the next state. So to update your set you would do something like:
const [set, setSet] = useState(new Set())
const itemToAdd = ' ', itemToRemove = ' ';
setSet(prev => new Set([...prev, itemToAdd]));
setSet(prev => new Set([...prev].filter(item => item !== itemToRemove)));
As you might notice, this makes adding and removing from a set as slow as a list. So unless you need to make a lot of checks with set.has() I'd recommend using a list:
const [items, setItems] = useState([])
const itemToAdd = ' ', itemToRemove = ' ';
setItems(prev => [...prev, itemToAdd]);
setItems(prev => prev.filter(item => item !== itemToRemove));
I'm trying to display the value of my inputs from a from, in a list. Everytime I hit submit, I expect that it should display the inputs in order.
The problem I'm having is that when I try to submit my form and display inputs in a list, it display an empty value first. On the next submit and thereafter, it displays the previous value, not the new one on the input field.
There's also an error message but i'm not understanding how to relate it to the problem. It's a warning message regarding controlled/uncontrolled components.
I've tried to add if statements to check for empty values in each functions but the problem persists.I've tried to manage the error massage by being consistent with all input to be controlled elements using setState, but nothing works.
I looked through todo list examples on github. I guess i'm trying to keep it in one functional component versus multiple ones, and I'm not using class components. I tried to follow the wesbos tutorial on Javascript 30 day challenge, day 15: Local Storage and Event Delegation. I'm trying to use React instead of plain JS.
Here's what my component looks like.
import React, { useEffect, useState } from "react";
import "../styles/LocalStorage.css";
export const LocalStorage = () => {
const [collection, setCollection] = useState([]);
const [value, setValue] = useState();
const [item, setItem] = useState({ plate: "", done: false });
const [display, setDisplay] = useState(false);
//set the value of the input
const handleChange = (e) => {
if (e.target.value === "") return;
setValue(e.target.value);
};
const handleSubmit = (e) => {
e.preventDefault();
if (value === "" || undefined) return;
setItem((prevState) => {
return { ...prevState, plate: value };
});
addItem(item);
setDisplay(true);
setValue("");
};
const addItem = (input) => {
if (input.plate === "") return;
setCollection([...collection, input]);
};
return (
<div>
<div className="wrapper">
<h2>LOCAL TAPAS</h2>
<ul className="plates">
{display ? (
collection.map((item, i) => {
return (
<li key={i}>
<input
type="checkbox"
data-index={i}
id={`item${i}`}
checked={item.done}
onChange={() =>
item.done
? setItem((state) => ({ ...state, done: false }))
: setItem((state) => ({ ...state, done: true }))
}
/>
<label htmlFor={`item${i}`}>{item.plate}</label>
</li>
);
})
) : (
<li>Loading Tapas...</li>
)}
</ul>
<form className="add-items" onSubmit={handleSubmit}>
<input
type="text"
name="item"
placeholder="Item Name"
required
value={value}
onChange={handleChange}
/>
<button type="submit">+ Add Item</button>
</form>
</div>
</div>
);
};
Since the setState function is asynchronous, you cannot use the state value item right after you fire the setItem(...). To ensure you get the latest value for your addItem function:
setItem((prevState) => {
const newItem = { ...prevState, plate: value };
addItem(newItem); // Now, it's getting the updated value!
return newItem;
});
And regarding the controlled and uncontrolled components, you can read the docs about it here. To fix your problem, you can initialize the value state with an empty string:
const [value, setValue] = useState('');