I was trying the useEffect example something like below:
useEffect(async () => {
try {
const response = await fetch(`https://www.reddit.com/r/${subreddit}.json`);
const json = await response.json();
setPosts(json.data.children.map(it => it.data));
} catch (e) {
console.error(e);
}
}, []);
and I get this warning in my console. But the cleanup is optional for async calls I think. I am not sure why I get this warning. Linking sandbox for examples. https://codesandbox.io/s/24rj871r0p
For React version <=17
I suggest to look at Dan Abramov (one of the React core maintainers) answer here:
I think you're making it more complicated than it needs to be.
function Example() {
const [data, dataSet] = useState<any>(null)
useEffect(() => {
async function fetchMyAPI() {
let response = await fetch('api/data')
response = await response.json()
dataSet(response)
}
fetchMyAPI()
}, [])
return <div>{JSON.stringify(data)}</div>
}
Longer term we'll discourage this pattern because it encourages race conditions. Such as — anything could happen between your call starts and ends, and you could have gotten new props. Instead, we'll recommend Suspense for data fetching which will look more like
const response = MyAPIResource.read();
and no effects. But in the meantime you can move the async stuff to a separate function and call it.
You can read more about experimental suspense here.
If you want to use functions outside with eslint.
function OutsideUsageExample({ userId }) {
const [data, dataSet] = useState<any>(null)
const fetchMyAPI = useCallback(async () => {
let response = await fetch('api/data/' + userId)
response = await response.json()
dataSet(response)
}, [userId]) // if userId changes, useEffect will run again
useEffect(() => {
fetchMyAPI()
}, [fetchMyAPI])
return (
<div>
<div>data: {JSON.stringify(data)}</div>
<div>
<button onClick={fetchMyAPI}>manual fetch</button>
</div>
</div>
)
}
For React version >=18
Starting with React 18 you can also use Suspense, but it's not yet recommended if you are not using frameworks that correctly implement it:
In React 18, you can start using Suspense for data fetching in opinionated frameworks like Relay, Next.js, Hydrogen, or Remix. Ad hoc data fetching with Suspense is technically possible, but still not recommended as a general strategy.
If not part of the framework, you can try some libs that implement it like swr.
Oversimplified example of how suspense works. You need to throw a promise for Suspense to catch it, show fallback component first and render Main component when promise it's resolved.
let fullfilled = false;
let promise;
const fetchData = () => {
if (!fullfilled) {
if (!promise) {
promise = new Promise(async (resolve) => {
const res = await fetch('api/data')
const data = await res.json()
fullfilled = true
resolve(data)
});
}
throw promise
}
};
const Main = () => {
fetchData();
return <div>Loaded</div>;
};
const App = () => (
<Suspense fallback={"Loading..."}>
<Main />
</Suspense>
);
When you use an async function like
async () => {
try {
const response = await fetch(`https://www.reddit.com/r/${subreddit}.json`);
const json = await response.json();
setPosts(json.data.children.map(it => it.data));
} catch (e) {
console.error(e);
}
}
it returns a promise and useEffect doesn't expect the callback function to return Promise, rather it expects that nothing is returned or a function is returned.
As a workaround for the warning you can use a self invoking async function.
useEffect(() => {
(async function() {
try {
const response = await fetch(
`https://www.reddit.com/r/${subreddit}.json`
);
const json = await response.json();
setPosts(json.data.children.map(it => it.data));
} catch (e) {
console.error(e);
}
})();
}, []);
or to make it more cleaner you could define a function and then call it
useEffect(() => {
async function fetchData() {
try {
const response = await fetch(
`https://www.reddit.com/r/${subreddit}.json`
);
const json = await response.json();
setPosts(json.data.children.map(it => it.data));
} catch (e) {
console.error(e);
}
};
fetchData();
}, []);
the second solution will make it easier to read and will help you write code to cancel previous requests if a new one is fired or save the latest request response in state
Working codesandbox
Until React provides a better way, you can create a helper, useEffectAsync.js:
import { useEffect } from 'react';
export default function useEffectAsync(effect, inputs) {
useEffect(() => {
effect();
}, inputs);
}
Now you can pass an async function:
useEffectAsync(async () => {
const items = await fetchSomeItems();
console.log(items);
}, []);
Update
If you choose this approach, note that it's bad form. I resort to this when I know it's safe, but it's always bad form and haphazard.
Suspense for Data Fetching, which is still experimental, will solve some of the cases.
In other cases, you can model the async results as events so that you can add or remove a listener based on the component life cycle.
Or you can model the async results as an Observable so that you can subscribe and unsubscribe based on the component life cycle.
You can also use IIFE format as well to keep things short
function Example() {
const [data, dataSet] = useState<any>(null)
useEffect(() => {
(async () => {
let response = await fetch('api/data')
response = await response.json()
dataSet(response);
})();
}, [])
return <div>{JSON.stringify(data)}</div>
}
void operator could be used here.
Instead of:
React.useEffect(() => {
async function fetchData() {
}
fetchData();
}, []);
or
React.useEffect(() => {
(async function fetchData() {
})()
}, []);
you could write:
React.useEffect(() => {
void async function fetchData() {
}();
}, []);
It is a little bit cleaner and prettier.
Async effects could cause memory leaks so it is important to perform cleanup on component unmount. In case of fetch this could look like this:
function App() {
const [ data, setData ] = React.useState([]);
React.useEffect(() => {
const abortController = new AbortController();
void async function fetchData() {
try {
const url = 'https://jsonplaceholder.typicode.com/todos/1';
const response = await fetch(url, { signal: abortController.signal });
setData(await response.json());
} catch (error) {
console.log('error', error);
}
}();
return () => {
abortController.abort(); // cancel pending fetch request on component unmount
};
}, []);
return <pre>{JSON.stringify(data, null, 2)}</pre>;
}
I read through this question, and feel the best way to implement useEffect is not mentioned in the answers.
Let's say you have a network call, and would like to do something once you have the response.
For the sake of simplicity, let's store the network response in a state variable.
One might want to use action/reducer to update the store with the network response.
const [data, setData] = useState(null);
/* This would be called on initial page load */
useEffect(()=>{
fetch(`https://www.reddit.com/r/${subreddit}.json`)
.then(data => {
setData(data);
})
.catch(err => {
/* perform error handling if desired */
});
}, [])
/* This would be called when store/state data is updated */
useEffect(()=>{
if (data) {
setPosts(data.children.map(it => {
/* do what you want */
}));
}
}, [data]);
Reference => https://reactjs.org/docs/hooks-effect.html#tip-optimizing-performance-by-skipping-effects
For other readers, the error can come from the fact that there is no brackets wrapping the async function:
Considering the async function initData
async function initData() {
}
This code will lead to your error:
useEffect(() => initData(), []);
But this one, won't:
useEffect(() => { initData(); }, []);
(Notice the brackets around initData()
For fetching from an external API using React Hooks, you should call a function that fetches from the API inside of the useEffect hook.
Like this:
async function fetchData() {
const res = await fetch("https://swapi.co/api/planets/4/");
res
.json()
.then(res => setPosts(res))
.catch(err => setErrors(err));
}
useEffect(() => {
fetchData();
}, []);
I strongly recommend that you do not define your query inside the useEffect Hook, because it will be re-render infinite times. And since you cannot make the useEffect async, you can make the function inside of it to be async.
In the example shown above, the API call is in another separated async function so it makes sure that the call is async and that it only happens once. Also, the useEffect's dependency array (the []) is empty, which means that it will behave just like the componentDidMount from React Class Components, it will only be executed once when the component is mounted.
For the loading text, you can use React's conditional rendering to validate if your posts are null, if they are, render a loading text, else, show the posts. The else will be true when you finish fetching data from the API and the posts are not null.
{posts === null ? <p> Loading... </p>
: posts.map((post) => (
<Link key={post._id} to={`/blog/${post.slug.current}`}>
<img src={post.mainImage.asset.url} alt={post.mainImage.alt} />
<h2>{post.title}</h2>
</Link>
))}
I see you already are using conditional rendering so I recommend you dive more into it, especially for validating if an object is null or not!
I recommend you read the following articles in case you need more information about consuming an API using Hooks.
https://betterprogramming.pub/how-to-fetch-data-from-an-api-with-react-hooks-9e7202b8afcd
https://reactjs.org/docs/conditional-rendering.html
try
const MyFunctionnalComponent: React.FC = props => {
useEffect(() => {
// Using an IIFE
(async function anyNameFunction() {
await loadContent();
})();
}, []);
return <div></div>;
};
Other answers have been given by many examples and are clearly explained, so I will explain them from the point of view of TypeScript type definition.
The useEffect hook TypeScript signature:
function useEffect(effect: EffectCallback, deps?: DependencyList): void;
The type of effect:
// NOTE: callbacks are _only_ allowed to return either void, or a destructor.
type EffectCallback = () => (void | Destructor);
// Destructors are only allowed to return void.
type Destructor = () => void | { [UNDEFINED_VOID_ONLY]: never };
Now we should know why effect can't be an async function.
useEffect(async () => {
//...
}, [])
The async function will return a JS promise with an implicit undefined value. This is not the expectation of useEffect.
Please try this
useEffect(() => {
(async () => {
const products = await api.index()
setFilteredProducts(products)
setProducts(products)
})()
}, [])
To do it properly and avoid errors: "Warning: Can't perform a React state update on an unmounted..."
useEffect(() => {
let mounted = true;
(async () => {
try {
const response = await fetch(`https://www.reddit.com/r/${subreddit}.json`);
const json = await response.json();
const newPosts = json.data.children.map(it => it.data);
if (mounted) {
setPosts(newPosts);
}
} catch (e) {
console.error(e);
}
})();
return () => {
mounted = false;
};
}, []);
OR External functions and using an object
useEffect(() => {
let status = { mounted: true };
query(status);
return () => {
status.mounted = false;
};
}, []);
const query = async (status: { mounted: boolean }) => {
try {
const response = await fetch(`https://www.reddit.com/r/${subreddit}.json`);
const json = await response.json();
const newPosts = json.data.children.map(it => it.data);
if (status.mounted) {
setPosts(newPosts);
}
} catch (e) {
console.error(e);
}
};
OR AbortController
useEffect(() => {
const abortController = new AbortController();
(async () => {
try {
const response = await fetch(`https://www.reddit.com/r/${subreddit}.json`, { signal: abortController.signal });
const json = await response.json();
const newPosts = json.data.children.map(it => it.data);
setPosts(newPosts);
} catch (e) {
if(!abortController.signal.aborted){
console.error(e);
}
}
})();
return () => {
abortController.abort();
};
}, []);
I know it is late but just I had the same problem and I wanted to share that I solved it with a function like this!
useEffect(() => {
(async () => {
try {
const response = await fetch(`https://www.reddit.com/r/${subreddit}.json`);
const json = await response.json();
setPosts(json.data.children.map(it => it.data));
} catch (e) {
console.error(e);
}
}) ()
}, [])
With useAsyncEffect hook provided by a custom library, safely execution of async code and making requests inside effects become trivially since it makes your code auto-cancellable (this is just one thing from the feature list). Check out the Live Demo with JSON fetching
import React from "react";
import { useAsyncEffect } from "use-async-effect2";
import cpFetch from "cp-fetch";
/*
Notice: the related network request will also be aborted
Checkout your network console
*/
function TestComponent(props) {
const [cancel, done, result, err] = useAsyncEffect(
function* () {
const response = yield cpFetch(props.url).timeout(props.timeout);
return yield response.json();
},
{ states: true, deps: [props.url] }
);
return (
<div className="component">
<div className="caption">useAsyncEffect demo:</div>
<div>
{done ? (err ? err.toString() : JSON.stringify(result)) : "loading..."}
</div>
<button className="btn btn-warning" onClick={cancel} disabled={done}>
Cancel async effect
</button>
</div>
);
}
export default TestComponent;
The same demo using axios
Just a note about HOW AWESOME the purescript language handles this problem of stale effects with Aff monad
WITHOUT PURESCRIPT
you have to use AbortController
function App() {
const [ data, setData ] = React.useState([]);
React.useEffect(() => {
const abortController = new AbortController();
void async function fetchData() {
try {
const url = 'https://jsonplaceholder.typicode.com/todos/1';
const response = await fetch(url, { signal: abortController.signal });
setData(await response.json());
} catch (error) {
console.log('error', error);
}
}();
return () => {
abortController.abort(); // cancel pending fetch request on component unmount
};
}, []);
return <pre>{JSON.stringify(data, null, 2)}</pre>;
}
or stale (from NoahZinsmeister/web3-react example)
function Balance() {
const { account, library, chainId } = useWeb3React()
const [balance, setBalance] = React.useState()
React.useEffect((): any => {
if (!!account && !!library) {
let stale = false
library
.getBalance(account)
.then((balance: any) => {
if (!stale) {
setBalance(balance)
}
})
.catch(() => {
if (!stale) {
setBalance(null)
}
})
return () => { // NOTE: will be called every time deps changes
stale = true
setBalance(undefined)
}
}
}, [account, library, chainId]) // ensures refresh if referential identity of library doesn't change across chainIds
...
WITH PURESCRIPT
check how useAff kills it's Aff in the cleanup function
the Aff is implemented as a state machine (without promises)
but what is relevant to us here is that:
the Aff encodes how to stop the Aff - You can put your AbortController here
it will STOP running Effects (not tested) and Affs (it will not run then from the second example, so it will NOT setBalance(balance)) IF the error was thrown TO the fiber OR INSIDE the fiber
Ignore the warning, and use the useEffect hook with an async function like this:
import { useEffect, useState } from "react";
function MyComponent({ objId }) {
const [data, setData] = useState();
useEffect(() => {
if (objId === null || objId === undefined) {
return;
}
async function retrieveObjectData() {
const response = await fetch(`path/to/api/objects/${objId}/`);
const jsonData = response.json();
setData(jsonData);
}
retrieveObjectData();
}, [objId]);
if (objId === null || objId === undefined) {
return (<span>Object ID needs to be set</span>);
}
if (data) {
return (<span>Object ID is {objId}, data is {data}</span>);
}
return (<span>Loading...</span>);
}
The most easy way is to use useAsyncEffect from 'use-async-effect'
You can find it on NPM.
const ProtectedRoute = ({ children }) => {
const [isAuth, setIsAuth] = useState(false);
useAsyncEffect(async () => {
try {
const data = await axios("auth");
console.log(data);
setIsAuth(true);
} catch (error) {
console.log(error);
}
}, []);
if (!isAuth)
return <Navigate to="/signin" />
return children;
}
I have a custom hook like so for getting data using useQuery. The hook works fine, no problem there.
const getData = async (url) => {
try{
return await axios(url)
} catch(error){
console.log(error.message)
}
}
export const useGetData = (url, onSuccess) => {
return useQuery('getData', () => getData(url), {onSuccess})
}
However, if I call this hook twice in my component it will only fetch data from the first call even with a different URL. (Ignore the comments typo, that's intentional)
The call in my component:
const { data: commentss, isLoading: commentsIsLoading } = useGetData(`/comments/${params.id}`)
const { data: forumPost, isLoading: forumPostIsLoading } = useGetData(`/forum_posts/${params.id}`)
When I console.log forumPost in this case, it is the array of comments and not the forum post even though I am passing in a different endpoint.
How can I use this hook twice to get different data? Is it possible? I know I can just call parallel queries but I would like to use my hook if possible.
Since useQuery caches based on the queryKey, use the URL in that name
const getData = async(url) => {
try {
return await axios(url)
} catch (error) {
console.log(error.message)
}
}
export const useGetData = (url, onSuccess) => {
return useQuery('getData' + url, () => getData(url), {
onSuccess
})
}
//........
const {
data: commentss,
isLoading: commentsIsLoading
} = useGetData(`/comments/${params.id}`)
const {
data: forumPost,
isLoading: forumPostIsLoading
} = useGetData(`/forum_posts/${params.id}`)
Im trying to debounce a api action which is a dispatch call to reducer.The api call in the browser should debounce after a particular delay given as a single api , but its going as multiple api calls after the delay ,the code is as follows.
please refer the screenshot also
const apiCall = (args) => {
dispatch(getECByStatus({status: 'PENDING_APPROVAL', search: args}))
}
const debounce = (apiFunc, delay) => {
let inDebounce
return function () {
const context = this
const args = arguments
clearTimeout(inDebounce)
inDebounce = setTimeout(() => {
inDebounce = null
apiFunc.apply(context, args)
},delay);
}
}
const optimizedVersion = debounce(apiCall, 600)
const handleSearchChange = (value) => {
optimizedVersion(value)
}
the handleSearchChange is the onchange event fired from the input box on typing the input.getECByStatus is a redux action creator, which calls api with the search param,
export const getECByStatus = (params) => async (dispatch) => {
let editCheckType = params?.type ? `/${params.type}` : ''
let searchParams = params?.search ? `&search=${params.search}` : ''
try {
dispatch({
type: actionType.GET_EC_BY_STATUS_REQUEST,
payload: {
load: true,
},
})
let study_id = getItem('study_id')
const { data } = await DataService.get(
`/edit-checks${editCheckType}?status=${params.status}&study_id=${study_id}${searchParams}`
)
dispatch({
type: actionType.GET_EC_BY_STATUS_SUCCESS,
payload: {
load: false,
data: data.data,
}
},
})
} catch (error) {
console.error('Get EC by status error', error)
dispatch({
type: actionType.GET_EC_BY_STATUS_FAIL,
payload: {
load: false,
},
})
}
}
Thanks in advance!
This is due to the UI re-render after dispatch event get fired, since the input box is a controlled one , we have to pass the updated value to the input box component, so we can make pass a ref for not re-rendering the UI.
I have a customHook with using useEffect and I would like it to return a result once useEffect is done, however, it always return before my async method is done...
// customHook
const useLoadData = (startLoading, userId, hasError) => {
const [loadDone, setLoadDone] = useState(false);
const loadWebsite = async(userId) => {
await apiService.call(...);
console.log('service call is completed');
dispatch(someAction);
}
useEffect(() => {
// define async function inside useEffect
const loadData = async () => {
if (!hasError) {
await loadWebsite();
}
}
// call the above function based on flag
if (startLoading) {
await loadData();
setLoadDone(true);
} else {
setLoadDone(false);
}
}, [startLoading]);
return loadDone;
}
// main component
const mainComp = () => {
const [startLoad, setStartLoad] = useState(true);
const loadDone = useLoadData(startLoad, 1, false);
useEffect(() => {
console.log('in useEffect loadDone is: ', loadDone);
if (loadDone) {
// do something
setStartLoad(false); //avoid load twice
} else {
// do something
}
}, [startLoad, loadDone]);
useAnotherHook(loadDone); // this hook will use the result of my `useLoadData` hook as an execution flag and do something else, however, the `loadDone` always false as returning from my `useLoadData` hook
}
It seems in my useDataLoad hook, it does not wait until my async function loadData to be finished but return loadDone as false always, even that I have put await keyword to my loadData function, and setLoadDone(true) after that, it still returns false always, what would be wrong with my implementation here and how could I return the value correct through async method inside customHook?
Well...it seems to be working after I put the setLoadDone(true); inside my async method, not inside useEffect, although I am not sure why...
updated code:
// customHook
const useLoadData = (startLoading, userId, hasError) => {
const [loadDone, setLoadDone] = useState(false);
const loadWebsite = async(userId) => {
await apiService.call(...);
console.log('service call is completed');
dispatch(someAction);
setLoadDone(true);
}
useEffect(() => {
// define async function inside useEffect
const loadData = async () => {
if (!hasError) {
await loadWebsite();
}
}
// call the above function based on flag
if (startLoading) {
await loadData();
// setLoadDone(true); doesn't work here
}
}, [startLoading]);
return loadDone;
}
I have a function that refreshes the data of my component when the function is called. At this moment it only works for one component at a time. But I want to refresh two components at once. This is my refresh function:
fetchDataByName = name => {
const { retrievedData } = this.state;
const { fetcher } = this.props;
const fetch = _.find(fetcher, { name });
if (typeof fetch === "undefined") {
throw new Error(`Fetch with ${name} cannot be found in fetcher`);
}
this.fetchData(fetch, (error, data) => {
retrievedData[name] = data;
this._isMounted && this.setState({ retrievedData });
});
};
My function is called like this:
refresh("meetingTypes");
As it it passed as props to my component:
return (
<Component
{...retrievedData}
{...componentProps}
refresh={this.fetchDataByName}
/>
);
I tried passing multiple component names as an array like this:
const args = ['meetingTypes', 'exampleMeetingTypes'];
refresh(args);
And then check in my fetchDataByName function if name is an array and loop through the array to fetch the data. But then the function is still executed after each other instead of at the same time. So my question is:
What would be the best way to implement this that it seems like the
function is executed at once instead of first refreshing meetingTypes
and then exampleMeetingTypes?
Should I use async/await or are there better options?
The fetchData function:
fetchData = (fetch, callback) => {
const { componentProps } = this.props;
let { route, params = [] } = fetch;
let fetchData = true;
// if fetcher url contains params and the param can be found
// in the component props, they should be replaced.
_.each(params, param => {
if (componentProps[param]) {
route = route.replace(`:${param}`, componentProps[param]);
} else {
fetchData = false; // don't fetch data for this entry as the params are not given
}
});
if (fetchData) {
axios
.get(route)
.then(({ data }) => {
if (this.isMounted) {
callback(null, data);
}
})
.catch(error => {
if (error.response.status == 403) {
this._isMounted && this.setState({ errorCode: 403 });
setMessage({
text: "Unauthorized",
type: "error"
});
}
if (error.response.status == 401) {
this._isMounted && this.setState({ errorCode: 401 });
window.location.href = "/login";
}
if (error.response.status != 403) {
console.error("Your backend is failing.", error);
}
callback(error, null);
});
} else {
callback(null, null);
}
};
I assume fetchData works asynchronously (ajax or similar). To refresh two aspects of the data in parallel, simply make two calls instead of one:
refresh("meetingTypes");
refresh("exampleMeetingTypes");
The two ajax calls or whatever will run in parallel, each updating the component when it finishes. But: See the "Side Note" below, there's a problem with fetchDataByName.
If you want to avoid updating the component twice, you'll have to update fetchDataByName to either accept multiple names or to return a promise of the result (or similar) rather than updating the component directly, so the caller can do multiple calls and wait for both results before doing the update.
Side note: This aspect of fetchDataByName looks suspect:
fetchDataByName = name => {
const { retrievedData } = this.state; // <=============================
const { fetcher } = this.props;
const fetch = _.find(fetcher, { name });
if (typeof fetch === "undefined") {
throw new Error(`Fetch with ${name} cannot be found in fetcher`);
}
this.fetchData(fetch, (error, data) => {
retrievedData[name] = data; // <=============================
this._isMounted && this.setState({ retrievedData });
});
};
Two problems with that:
It updates an object stored in your state directly, which is something you must never do with React.
It replaces the entire retrievedData object with one that may well be stale.
Instead:
fetchDataByName = name => {
// *** No `retrievedData` here
const { fetcher } = this.props;
const fetch = _.find(fetcher, { name });
if (typeof fetch === "undefined") {
throw new Error(`Fetch with ${name} cannot be found in fetcher`);
}
this.fetchData(fetch, (error, data) => {
if (this._isMounted) { // ***
this.setState(({retrievedData}) => ( // ***
{ retrievedData: {...retrievedData, [name]: data} } // ***
); // ***
} // ***
});
};
That removes the in-place mutation of the object with spread, and uses an up-to-date version of retrievedData by using the callback version of setState.