I’ve encountered a problem with a React hook from the "react-moralis" SDK and need some help.
I’ve implemented the useWeb3Contract hook from the package in an exported function, which should return the result (data) of the function call after fetching the data successfully. However, the function seems to be returning before the data gets fetched successfully.
Here is the code of the function:
import { useEffect } from "react"
import { useWeb3Contract } from "react-moralis"
import { abi as tokenAbi } from "../../constants/ERC20"
export default function useRetrieveTokenSymbol(address) {
const {
runContractFunction: fetch,
data,
isFetching,
isLoading,
} = useWeb3Contract({
abi: tokenAbi,
contractAddress: address,
functionName: "symbol",
params: {},
})
const retrieve = async () => {
await fetch()
}
useEffect(() => {
retrieve()
}, [])
if (!isFetching && !isLoading && data) return data
}
This function then gets called in a separate react component, where it should only return the data from the useWeb3Contract hook, which then can be stored in a variable.
That looks like that:
export default function TokenSymbol({tokenAddress}) {
const tokenSymbol = useRetrieveTokenSymbol(tokenAddress)
return (
<div>{tokenSymbol}</div>
)
}
tokenSymbol however always is undefined, because the useRetrieveTokenSymbol function returns before finishing fetching the data and then returns an undefined data constant. The conditional if statement gets completely ignored and I simply cannot figure out why.
Any of you guys know a fix to this? Would really appreciate it :)
You should wrap the values you are tracking in state. That way, when they update, the hook will cause a re-render:
const [myData, setMyData] = useState(data);
useEffect(() => {
setMyData(data);
}, [data]);
return myData;
Related
I'm creating a react app with redux.
I need the lists of french departements for all pages in my app, so I put it in redux state.
I dispatch the action in the App component in the useEffect hook (Note I use an other useEffect in the component, but when the action is in the other block it's not working too)
I have a page where I need to use this list, so I select it with the useSelector hook.
But it returns an empty object, I have an error telling me dpts.map is not a function
I think the action is dispatching after the page has rendered, because I when I log the response of the api call in the action, it appears after the log of the useSelector result.
I'm using another state property in another page, but it seems to work with the other page.
App.jsx
const dispatch = useDispatch();
useEffect(() => {
dispatch(getDpts());
}, [dispatch])
Here is the action associated with :
dpts.actions.js
import axios from "axios";
export const GET_DPTS = "GET_DPTS";
export const getDpts = () => {
return async (dispatch) => {
try {
const res = await axios({
method: "get",
url: "https://geo.api.gouv.fr/departements",
});
console.log("done : " + res)
dispatch({ type: GET_DPTS, payload: res.data });
} catch (err) {
(err) => console.log("DPTS FETCH ERROR --- " + err);
}
};
};
Map.jsx
function DptCtl() {
// Control
const map = useMap();
// List of dpts and provinces
const dpts= useSelector(dptsSelector);
console.log(dpts);
return (
<>
<input type="text" list="dpt-ctl-list" placeholder="Filtrer par département"/>
<datalist id="dpt-ctl-list">
{dpts.map((dpt, index) =>
<option value={dpt.code} key={index}>{dpt.nom}</option>
)}
</datalist>
</>
)
}
It depends on how you are initializing your state in the reducer.
for example you create a reducer with this initial state:
const initialState={}
later, based on actions, the state changes to this:
{dpts:someDataArray}
the problem is that you have a dpts.map somewhere in your app, since dpts is undefined in the beginning you receive that error that dpts.map is not a function.
the solution to this is simply put dpts in the initialState as an empty array:
const initialState={dpts:[]}
if that is not the issue with your code, meaning dpts isn't undefined in the initialState, it is probably initialized as a string or an object which don't have map methods.
dear community, I am facing a wired issue, and I don't know how to summary my situation in the question title, so I wonder if the question title is accurate enough.
I was trying to convert a class component to a hook component.
The class version code like this
async componentDidMount() {
const { dispatch, itemId } = this.props;
try {
if (itemId) {
await dispatch({
type: 'assignment/fetchSubmissionsByAssignment', //here to fetch submissions in props
payload: {
id: itemId
}
});
}
const { submissions } = this.props;
this.setState({
studentSubmissions: submissions,
});
} catch (error) {
throw error.message;
}
}
render() {
const { studentSubmissions } = this.state;
return (
<Table dataSource={studentSubmissions} />
)
}
export default SubmissionsDetail;
and in hook, it look like this
const [studentSubmissions, setStudentSubmissions] = useState([]);
useEffect(() => {
async function fetchSubmissions() {
const { dispatch, itemId } = props;
try {
if (itemId) {
await dispatch({
type: 'assignment/fetchSubmissionsByAssignment',
payload: {
id: itemId
}
});
}
const { submissions } = props;
setStudentSubmissions(submissions)
} catch (error) {
throw error.message;
}
};
fetchSubmissions()
}, []);
return (
<Table dataSource={studentSubmissions} />
)
export default SubmissionsDetail;
I omitted some code for better reading, like connect to redux store or others.
and the component is import in the parent file like this
import SubmissionsDetail from './SubmissionsDetail'
{assignmentIds.map((itemId) => {
<SubmissionsDetail itemId={itemId}/>
})}
it work perfect in class component, the expected result should return tables like this
However, when I change to use hook, the result return like this
or sometimes all data in tables become submissions3
I try to console.log(submissions) inside the try{...} block, when in class, the result is
which is correct, there have two assignments, the one have 4 submissions, another one have zero submission.
But the output in hook is different, the result is like this
either both have 4 submissions, either both have zero. That means one obj affect all other obj.
It seems like if useState change, it would influence other objs, that make me really confused. I think in the map method, each item is independent, right? If so, and how to explain why it work perfectly in class setState, but failed in hook useState?
I hope my question is clear enough, If you know how to describe my question in short, plz let me know, I would update the title, to help locate experts to answer.
Please don't hesitate to share your opinions, I really appreciate and need your help, many thanks!
Edit: You are probably going to want to rework the way you store the submission inside of the redux store if you really want to use the Hook Component. It seems like right now, submissions is just an array that gets overwritten whenever a new API call is made, and for some reason, the Class Component doesn't update (and it's suppose to update).
Sorry it's hard to make suggestions, your setup looks very different than the Redux environments I used. But here's how I would store the submissions:
// no submissions loaded
submissions: {}
// loading new submission into a state
state: {
...state,
sessions: {
...state.session,
[itemId]: data
}
}
// Setting the state inside the component
setStudentSubmissions(props.submissions[itemId])
And I think you will want to change
yield put({
type: 'getSubmissions',
payload: response.data.collections
});
to something like
yield put({
type: 'getSubmissions',
payload: {
data: response.data.collections,
itemId: id
});
If you want to try a "hack" you can maybe get a useMemo to avoid updating? But again, you're doing something React is not suppose to do and this might not work:
// remove the useEffect and useState, and import useMemo
const studentSubmissions = useMemo(async () => {
try {
if (itemId) {
await dispatch({
type: "assignment/fetchSubmissionsByAssignment", //here to fetch submissions in props
payload: {
id: itemId,
},
});
return this.props.submissions;
}
return this.props.submissions;
} catch (error) {
throw error.message;
}
}, []);
return (
<Table dataSource={studentSubmissions} />
)
export default SubmissionsDetail;
There is no reason to use a local component state in either the class or the function component versions. All that the local state is doing is copying the value of this.props.submissions which came from Redux. There's a whole section in the React docs about why copying props to state is bad. To summarize, it's bad because you get stale, outdated values.
Ironically, those stale values were allowing it to "work" before by covering up problems in your reducer. Your reducer is resetting the value of state.submissions every time you change the itemId, but your components are holding on to an old value (which I suspect is actually the value for the previous component? componentDidMount will not reflect a change in props).
You want your components to select a current value from Redux based on their itemId, so your reducer needs to store the submissions for every itemId separately. #Michael Hoobler's answer is correct in how to do this.
There's no problem if you want to keep using redux-saga and keep using connect but I wanted to give you a complete code so I am doing it my way which is with redux-toolkit, thunks, and react-redux hooks. The component code becomes very simple.
Component:
import React, { useEffect } from "react";
import { fetchSubmissionsByAssignment } from "../store/slice";
import { useSelector, useDispatch } from "../store";
const SubmissionsDetail = ({ itemId }) => {
const dispatch = useDispatch();
const submissions = useSelector(
(state) => state.assignment.submissionsByItem[itemId]
);
useEffect(() => {
dispatch(fetchSubmissionsByAssignment(itemId));
}, [dispatch, itemId]);
return submissions === undefined ? (
<div>Loading</div>
) : (
<div>
<div>Assignment {itemId}</div>
<div>Submissions {submissions.length}</div>
</div>
);
};
export default SubmissionsDetail;
Actions / Reducer:
import { createAsyncThunk, createReducer } from "#reduxjs/toolkit";
export const fetchSubmissionsByAssignment = createAsyncThunk(
"assignment/fetchSubmissionsByAssignment",
async (id) => {
const response = await getSubmissionsByAssignment(id);
// can you handle this in getSubmissionsByAssignment instead?
if (response.status !== 200) {
throw new Error("invalid response");
}
return {
itemId: id,
submissions: response.data.collections
};
}
);
const initialState = {
submissionsByItem: {}
};
export default createReducer(initialState, (builder) =>
builder.addCase(fetchSubmissionsByAssignment.fulfilled, (state, action) => {
const { itemId, submissions } = action.payload;
state.submissionsByItem[itemId] = submissions;
})
// could also respond to pending and rejected actions
);
if you have an object as state, and want to merge a key to the previous state - do it like this
const [myState, setMyState] = useState({key1: 'a', key2: 'b'});
setMyState(prev => {...prev, key2: 'c'});
the setter of the state hook accepts a callback that must return new state, and this callback recieves the previous state as a parameter.
Since you did not include large part of the codes, and I assume everything works in class component (including your actions and reducers). I'm just making a guess that it may be due to the omission of key.
{assignmentIds.map((itemId) => {
<SubmissionsDetail itemId={itemId} key={itemId} />
})}
OR it can be due to the other parts of our codes which were omitted.
so i have a bit of a weird problem i dont know how to solve.
In my code i have a custom hook with a bunch of functionality for a fetching a list
of train journeys. I have some useEffects to that keeps loading in new journeys untill the last journey of the day.
When i change route, while it is still loading in new journeys. I get the "changes to unmounted component" React error.
I understand that i get this error because the component is doing an async fetch that finishes after i've gone to a new page.
The problem i can't figure out is HOW do i prevent it from doing that? the "unmounted" error always occur on one of the 4 lines listed in the code snippet.
Mock of the code:
const [loading, setLoading] = useState(true);
const [journeys, setJourneys] = useState([]);
const [hasLaterDepartures, setHasLaterDepartures] = useState(true);
const getJourneys = async (date, journeys) => {
setLoading(true);
setHasLaterDepartures(true);
const selectedDateJourneys = await fetchJourney(date); // Fetch that returns 0-3 journeys
if (condition1) setHasLaterDepartures(false); // trying to update unmounted component
if (condition2) {
if (condition3) {
setJourneys(something1); // trying to update unmounted component
} else {
setJourneys(something2) // trying to update unmounted component
}
} else {
setJourneys(something3); // trying to update unmounted component
}
};
// useEffects for continous loading of journeys.
useEffect(() => {
if (!hasLaterDepartures) setLoading(false);
}, [hasLaterDepartures]);
useEffect(() => {
if (hasLaterDepartures && journeys.length > 0) {
const latestStart = ... // just a date
if (latestStart.addMinutes(5).isSameDay(latestStart)) {
getJourneys(latestStart.addMinutes(5), journeys);
} else {
setLoading(false);
}
}
}, [journeys]);
I can't use a variable like isMounted = true in the useEffect beacuse it would reach inside the if statement and reach a "setState" by the time i'm on another page.
Moving the entire call into a useEffect doesn't seem to work either. I am at a loss.
Create a variable called mounted with useRef, initialised as true. Then add an effect to set mounted.current to false when the component unmounts.
You can use mounted.current anywhere inside the component to see if it's mounted, and check that before setting any state.
useRef gives you a variable you can mutate but which doesn't cause a rerender.
When you use useEffect hook with action which can be done after component change you should also take care about clean effect when needed. Maybe example help you, also check this page.
useEffect(() => {
let isClosed = false
const fetchData = async () => {
const data = await response.json()
if ( !isClosed ) {
setState( data )
}
};
fetchData()
return () => {
isClosed = true
};
}, []);
In your use case, you probably want to create a Store that doesn't reload everytime you change route (client side).
Example of a store using useContext();
const MyStoreContext = createContext()
export function useMyStore() {
const context = useContext(MyStoreContext)
if (!context && typeof window !== 'undefined') {
throw new Error(`useMyStore must be used within a MyStoreContext`)
}
return context
}
export function MyStoreProvider(props) {
const [ myState, setMyState ] = useState()
//....whatever codes u doing with ur hook.
const exampleCustomFunction = () => {
return myState
}
const getAllRoutes = async (mydestination) => {
return await getAllMyRoutesFromApi(mydestination)
}
// you return all your "getter" and "setter" in value props so you can use them outside the store.
return <MyStoreContext.Provider value={{ myState, setMyState, exampleCustomFunction, getAllRoutes }}>{props.children}</MyStoreContext.Provider>
}
You will wrap the store around your entire App, e.g.
<MyStoreProvider>
<App />
</MyStoreProvider>
In your page where you want to use your hook, you can do
const { myState, setMyState, exampleCustomFunction, getAllRoutes } = useMyStore()
const onClick = async () => getAllRouters(mydestination)
Considering if you have client side routing (not server side), this doesn't get reloaded every time you change your route.
I'm working with React and Apollo and I'm trying to initialize state with data fetched using useQuery hook but I'm getting "Cannot read property 'map' of undefined" when loading the page.
const { loading, error, data } = useQuery(FETCH_BLOGS);
const [state, setState] = useState(undefined);
useEffect(() => {
if (loading === false && data) {
setState(data.blogs);
}
}, [loading, data]);
if (loading) return <p>Loading...</p>;
if (error) return <p>Error</p>;
In the JSX I'm calling {renderBlogs(state)} which maps over the array and is where the error is being thrown. If I pass in the initial data {renderBlogs(data.blogs)} it works but I need to store the data in state as it will be mutated.
When I console.log(state) it logs 2 lines:
The first is undefined.
The second is the array of blogs (as shown in the screenshot).
It appears that the page is trying to render the initial state (undefined) before before the state is set to the query data. Is this the case? I thought using useEffect would solve this but that doesn't seem to be the case. Any help is appreciated, thank you.
To quote the useEffect documentation:
The function passed to useEffect will run after the render is committed to the screen. Think of effects as an escape hatch from React’s purely functional world into the imperative world.
The problem is that useEffect will trigger after a render. This will result in the following chain of events. Assume loading is just set to false and there where no errors fetching the data.
When the component is now being rendered both the if (loading) and if (error) guard clauses will be skipped, because the data successfully loaded. However state is not yet updated because the useEffect callback will trigger after the current render. At this point when you call renderBlogs(state) state will still be undefined. This will trow the error you describe.
I might be missing some context, but from what is shown in the question there is no reason to use useEffect. Instead use data directly.
The example provided by Apollo for useQuery provides a good starting point:
import { gql, useQuery } from '#apollo/client';
const GET_GREETING = gql`
query GetGreeting($language: String!) {
greeting(language: $language) {
message
}
}
`;
function Hello() {
const { loading, error, data } = useQuery(GET_GREETING, {
variables: { language: 'english' },
});
if (loading) return <p>Loading ...</p>;
return <h1>Hello {data.greeting.message}!</h1>;
}
Applying the example to your scenario it might look very similar.
const { loading, error, data } = useQuery(FETCH_BLOGS);
if (loading) return <p>Loading...</p>;
if (error) return <p>Error</p>;
return renderBlogs(data.blogs);
If you need the setter you might want to provide a bit more context to the question. However a common reason to have a setter might be if you want to apply some sort of filter. A simple solution would be to have a computed blogs state.
const filteredBlogs = data.blogs.filter(blog => blog.title.includes(search));
Here search would be the state of some <input value={search} onChange={handleSearchChange} /> element. To improve performance you could also opt to use useMemo here.
const filteredBlogs = useMemo(() => (
data.blogs.filter(blog => blog.title.includes(search))
), [data.blogs, search]);
If you really need to use useState for some reason, you could try the onCompleted option of useQuery instead of useEffect.
const [blogs, setBlogs] = useState();
const { loading, error } = useQuery(FETCH_BLOGS, {
onCompleted: data => setBlogs(data.blogs),
});
With data fetching in React, the following is a common warning:
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 a useEffect cleanup function. in ParentComponent
I've read multiple posts and suggestions on how to handle this, and none are working currently.
For this, we have the function useAxiosApi which fetches data asynchronously, and ParentComponent which is the component that uses the useAxiosApi() and needs the data. ParentComponent is the component being unmounted / being referenced in the warnings.
Parent Component
import useAxiosApi...
function ParentComponent({ info }) {
const dataConfig = { season: info.season, scope: info.scope };
const [data, isLoading1, isError1] = useAxiosApi('this-endpoint', [], dataConfig);
return (
{isLoading && <p>We are loading...</p>}
{!isLoading &&
... use the data to render something...
}
)
}
useAxiosApi
import axios from 'axios';
import { useState } from 'react';
import useDeepCompareEffect from 'use-deep-compare-effect';
const resources = {};
const useAxiosApi = (endpoint, initialValue, config) => {
// Set Data-Fetching State
const [data, setData] = useState(initialValue);
const [isLoading, setIsLoading] = useState(true);
const [isError, setIsError] = useState(false);
// Use in lieu of useEffect
useDeepCompareEffect(() => {
// Token/Source should be created before "fetchData"
let source = axios.CancelToken.source();
let isMounted = true;
// Create Function that makes Axios requests
const fetchData = async () => {
// For Live Search on keystroke, Save Fetches and Skip Fetch if Already Made
if (endpoint === 'liveSearch' && resources[config.searchText]) {
return [resources[config.searchText], false, false];
}
// Otherwise, Continue Forward
setIsError(false);
setIsLoading(true);
try {
const url = createUrl(endpoint, config);
const result = await axios.get(url, { cancelToken: source.token });
console.log('isMounted: ', isMounted);
if (isMounted) {
setData(result.data);
}
// If LiveSearch, store the response to "resources"
if (endpoint === 'liveSearch') {
resources[config.searchText] = result.data;
}
} catch (error) {
setIsError(true);
} finally {
setIsLoading(false);
}
};
// Call Function
fetchData();
// Cancel Request if needed in cleanup function
return () => {
console.log('Unmount or New Search? About to call source.cancel()');
isMounted = false; // is this doing its job?
source.cancel();
};
}, [endpoint, config]);
// Return as length-3 array
return [data, isLoading, isError];
};
export default useAxiosApi;
createUrl is simply a function that takes the endpoint and dataConfig and creates the url that axios will fetch from. Note that our cancelTokens seem to be working in conjunction with the Live search, as new searches are cancelling the old search queries, and the saving of data results into resources for the one specific endpoint liveSearch works as well.
However, our problem is that when ParentComponent is unmounted quickly, before the data fetch is complete, we still receive the Cant perform a React state update warning. I've checked the console.logs(), and console.log('isMounted: ', isMounted) is always returning true, even if we unmount the component quickly after it is mounted / before data fetching is complete.
We're at a loss on this, as using the isMounted variable is the way that I've seen this problem handled before. Perhaps there's a problem with the useDeepCompareEffect hook? Or maybe we're missing something else.
Edit: Weve also tried to create the isMounted variable from inside of ParentComponent, and pass that as a parameter into the useAxiosApi function, however this did not work for us either... In general, it would be much better if we can handle this warning via an update to our useAxiosApi function, as opposed to in the ParentComponent.
Edit2: It seems like the cancelToken only works when a duplicate API call is fired off to the same endpoint. This is good for our liveSearch, however it means that all of the other fetches are not cancelled.