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'm kind of confused about how useEffect is triggered and how it work. I wrote a function like this but the useEffect doesn't run at all. I want to fetch the data from the API and then render a page based on the data. But it doesn't trigger the useEffect. If I don't use the useEffect, it will render the page three times.
async function getData() {
var tmpArrData = [];
await fetch("this API is hidden due to the privacy of the company - sorry")
.then((res) => res.json())
.then((data) => {
console.log("data", data);
tmpArrData = data;
});
console.log("tmpData ", tmpArrData);
return tmpArrData;
}
function App() {
const [arrData, setArrData] = useState();
const [loadData, setLoadData] = useState(false);
useEffect(() => {
console.log("if it works, this line should be shown");
const tmpArrData = getData();
setArrData(tmpArrData);
}, [arrData]);
const data = arrData[0];
console.log(data);
return (
<GifCompoment
id = {data.id}
name = {data.name}
activeTimeTo = {data.activeTimeTo}
activeTimeFrom = {data.activeTimeFrom}
requiredPoints = {data.requiredPoints}
imageUrl = {data.imageUrl}
/>
);
}
export default App;
The useEffect hook is guaranteed to run at least once at the end of the initial render.
getData is an async function and the useEffect callback code is not waiting for it to resolve. Easy solution is to chain from the implicitly returned Promise from getData and access the resolved value to update the arrData state. Make sure to remove the state from the useEffect's dependency array so that you don't create a render loop.
The getData implementation could be clean/tightened up by just returning the fetch result, no need to save into a temp variable first.
async function getData() {
return await fetch(".....")
.then((res) => res.json());
}
useEffect(() => {
console.log("if it works, this line should be shown");
getData().then((data) => {
setArrData(data);
});
}, []); // <-- empty dependency so effect called once on mount
Additionally, since arrData is initially undefined, arrData[0] is likely to throw an error. You may want to provide valid initial state, and a fallback value in case the first element is undefined, so you don't attempt to access properties of an undefined object.
const [arrData, setArrData] = useState([]);
...
const data = arrData[0] || {}; // data is at least an object
return (
<GifCompoment
id={data.id}
name={data.name}
activeTimeTo={data.activeTimeTo}
activeTimeFrom={data.activeTimeFrom}
requiredPoints={data.requiredPoints}
imageUrl={data.imageUrl}
/>
);
You should call state setter insede of Promise
function App() {
const [arrData, setArrData] = useState();
function getData() {
fetch("/api/hidden")
.then((res) => res.json())
.then((data) => setArrData(data));
}
useEffect(() => {
console.log("if it works, this line should be shown");
getData();
}, []);
return ...
}
By combining the answer from Drew Reese and Artyom Vancyan, I have solved my problem. I think the key points are setState right in the then function .then((data) => setArrData(data)) ,don't put the dependency in the useEffect, and await inside the useEffect. Thank you guy super ultra very much. Big love
useEffect(() => {
console.log("if it works, this line should be shown");
const getData = async () => {
await fetch("hidden API")
.then((ref) => ref.json())
.then((data) => {
setArrData(data);
});
}
getData();
}, []);
function App() {
const [arrData, setArrData] = useState([]);
const [loadData, setLoadData] = useState(false);
const async getData=()=> {
var tmpArrData = [];
await fetch("this API is hidden due to the privacy of the company - sorry")
.then((res) => res.json())
.then((data) => {
console.log("data", data);
setArrData(tmpArrData);
});
console.log("tmpData ", tmpArrData);
return tmpArrData;
}
useEffect(() => {
console.log("if it works, this line should be shown");
const callApi =async()=>{
await getData();
}
}, [arrData]);
const data = arrData[0];
console.log(data);
return (
<GifCompoment
id = {data.id}
name = {data.name}
activeTimeTo = {data.activeTimeTo}
activeTimeFrom = {data.activeTimeFrom}
requiredPoints = {data.requiredPoints}
imageUrl = {data.imageUrl}
/>
);
}
export default App;
Page will be rendered three to four times it's normal.
I'm trying to fetch some data with Axios and React, But I'm having a problem resolving the promise and setting it on the state, that's weird.
Here is the Base:
export const fetchUserById = (username) => client.get(`/${username}`);
Here is the Call:
export const getUserById = async (username) => {
try {
const response = await api.fetchUserById(username);
const data = await response.data;
return data;
} catch (error) {
return error;
}
};
Here is in React:
const [user, setUser] = useState();
useEffect(() => {
const data = getUserById(params.username); // this gets the username and its working
setUser(data)
}, [])
useEffect(() => {
console.log("this is user: ", user)
}, [user])
If I console log user, I get undefined, If I console log data i get a promise.
getUserById is declared async so it implicitly returns a Promise that callers should either await or use a Promise chain on.
useEffect(() => {
const data = getUserById(params.username);
setUser(data); // <-- logs only the returned Promise object!
}, [])
async/await
useEffect(() => {
const getUser = async () => {
try {
const data = await getUserById(params.username);
setUser(data);
} catch(error) {
// handle error, log, etc...
}
};
getUser();
}, []);
Promise chain
useEffect(() => {
getUserById(params.username)
.then(data => {
setUser(data);
})
.catch(error => {
// handle error, log, etc...
});
};
}, []);
Or you could as well do:
useEffect(() => {
// fetch data
(async () => {
try {
const data = await getUserById(params.username);
// set state
setUser(data)
} catch(error) {
// handle error, log, etc...
// set init state
setUser(null)
}
})();
}, []);
I am new to react and try to get data from the database and view data in frontend. This is the code I tried.
function ViewPost() {
const { postId } = useParams();
console.log(postId);
const [post, setPost] = useState({});
useEffect(()=>{
getOnePost();
}, []);
useEffect(()=>{
if (post && post.location) {
console.log(post.location);
console.log(post.location.longitude);
console.log(post.location.latitude);
}
}, [post]);
const getOnePost = async () => {
try {
const response = await axios.get(`/buyerGetOnePost/${postId}`)
console.log(response);
const allPost=response.data.onePost;
setPost(allPost);
} catch (error) {
console.error(`Error: ${error}`)
}
}
console.log(post);
console.log(post.wasteItemList);
const [offers, setOffers] = useState([]);
useEffect(()=>{
getAllOffers();
}, []);
const getAllOffers = async () => {
await axios.get(`/viewPendingSellerOffers`)
.then ((response)=>{
const allNotes=response.data.existingOffers;
setOffers(allNotes);
})
.catch(error=>console.error(`Error: ${error}`));
}
console.log(offers);
const wasteItem = offers?.filter(wasteItems => wasteItems.status==='accepted' && wasteItems.wasteItemsListId===post?.wasteItemList?._id);
console.log(wasteItem);
}
When I call the first API I get these results. This is an image of results.
In the above image, there is a length 2 array of objects called as wasteItemList. Then I call the second API and get these results.
This image shows length 8 array of objects. Then I try to filter the data of these two arrays using this const wasteItem = offers?.filter(wasteItems => wasteItems.status === 'accepted' && wasteItems.wasteItemsListId === post?.wasteItemList?._id); code. But I get a length 0 empty array as the results of this filter function. But when I try an ID of a wasteItemList array
6112679258125b0418844368 instead of using this post?.wasteItemList?._id code I get the correct result. What is the problem here? How do I solve this problem?
Edited code:
function ViewPost() {
const { postId } = useParams();
const [post, setPost] = useState(undefined);
const [offers, setOffers] = useState(undefined);
useEffect(() => {
setPost(undefined);
axios
.get(`/buyerGetOnePost/${postId}`)
.then((resp) => setPost(resp.data.onePost))
.catch((err) => console.error(err));
}, [postId]);
useEffect(() => {
axios
.get(`/viewPendingSellerOffers`)
.then((response) => setOffers(response.data.existingOffers))
.catch((err) => console.error(err));
}, []);
useEffect(()=>{
if (post && post.location) {
console.log(post.location);
console.log(post.location.longitude);
console.log(post.location.latitude);
}
}, [post]);
console.log(post);
console.log(post?.wasteItemList);
console.log(offers);
const wasteItem = offers?.filter(wasteItems => wasteItems.status==='accepted' && wasteItems.wasteItemsListId===post?.wasteItemList?._id);
console.log(wasteItem);
}
useEffect runs asynchronously so your post will not be available
on your getAllOffers function which is located in your second
useEffect.
You will need to make your getOnePost() and getAllOffers() to
run synchronously within a single useEffect.
Or the problem is in your condition checks as I can't tell much only
by your given array picture.
I'm trying to get the data of "body" outside of the fetchUserData() function.
I just want to store it in an variable for later use.
Also tried modifying state, but didn't work either.
Thanks for your help :)
const [userData, setUserData] = useState();
async function fetchUserData () {
try {
const result = await fetch(`/usermanagement/getdocent`, {
method: "GET"
});
const body = await result.json();
//setUserData(body);
return(
body
)
} catch (err) {
console.log(err);
}
}
let userTestData
fetchUserData().then(data => {userTestData = data});
console.log(userTestData);
//console.log(userData);
Use useEffect
async function fetchUserData () {
try {
const result = await fetch(`/usermanagement/getdocent`, {
method: "GET"
})
return await result.json()
} catch (err) {
console.log(err)
return null
}
}
const FunctionalComponent = () => {
const [userData, setUserData] = useState()
useEffect(() => {
fetchUserData().then(data => {
data && setUserData(data)
})
}, []) // componentDidMount
return <div />
}
Ben Awad's awesome tutorial
Example:
it seems that you are making it more complicated than it should be. When you get the response i.e the resolved promise with the data inside the async function, just set the state and in the next render you should get the updated data.
Example:
const [userData, setUserData] = useState();
useEffect(() => {
const getResponse = async () => {
try {
const result = await fetch(`/usermanagement/getdocent`, {
method: "GET"
});
const body = await result.json();
setUserData(body);
} catch (err) {
console.log(err)
}
}
getResponse();
}, [])
console.log(userData);
return <div></div>
Assuming the you need to call the function only once define and call it inside a useEffect or 'componentDidMount'. For using async function inside useEffect we need to define another function and then call it.
When you do
let userTestData
// This line does not wait and next line is executed immediately before userTestData is set
fetchUserData().then(data => {userTestData = data});
console.log(userTestData);
// Try changing to
async someAsyncScope() {
const userTestData = await fetchUserData();
console.log(userTestData)
}
Example:
state = {
someKey: 'someInitialValue'
};
async myAsyncMethod() {
const myAsyncValue = await anotherAsyncMethod();
this.setState({ someKey: myAsyncValue });
}
/*
* Then in the template or where ever, use a state variable which you update when
* the promise resolves. When a state value is used, once the state is updated,
* it triggers as a re-render
*/
render() {
return <div>{this.state.someKey}</div>;
}
In your example you'd use setUserData instead of this.setState and userData instead of {this.state.someKey}