I am making a get request to get data from my rest API, and when I have the data react will keep on making the same request simultaneously multiple times.
this is the code:
export default function Transaction() {
const [transactions, setTransaction] = useState([]);
const [loading, setLoading] = useState(true)
const { id } = useParams();
// this is where I am getting the problem
useEffect(() => {
const fetchTransc = async () => {
const res = await axios.get(`http://localhost:4000/api/get-records/${id}`);
setTransaction(res.data)
setLoading(false)
console.log(res.data)
};
fetchTransc();
},[id,transactions]);
The second argument of the UseEffect hook is the dependency array. It tells react which variables to watch for changes. When a dependency changes or when the component is mounted for the first time, the code inside the hook is executed.
In your case the array indicates that each time “id” or “transations” change, the hook should be executed.
Since setTransation is called in the fetch function, that will trigger the hook again because “transations” is present in hook’s the dependency array.
Each time the transactions state variable is set with a brand a new object fetched from the url, react will trigger the useEffect hook.
If “transations” is removed from the hook’s dependency array, this should work fine. Maybe also adding an IF to check the “id” value could be useful to prevent errors.
useEffect(() => {
const fetchTransc = async () => {
if(id != null) {
const res = await axios.get(`http://localhost:4000/api/get-records/${id}`);
setTransaction(res.data)
setLoading(false)
console.log(res.data)
}
};
fetchTransc();
},[id]);
Related
I expected to get the url with category=business,but the web automatically reset my state to the url that dosent have the category.I dont know the reason behind
let {id}=useParams()
const [newsurl,setNewsurl]=useState(()=>{
const initialstate="https://newsapi.org/v2/top-headlines?country=us&apiKey=c75d8c8ba2f1470bb24817af1ed669ee"
return initialstate;})
//console.log(id);
const [articles, setActicles] = useState([]);
useEffect( ()=>{
if(id === 2)
console.log("condition")
setNewsurl("https://newsapi.org/v2/top-headlines?country=de&category=business&apiKey=c75d8c8ba2f1470bb24817af1ed669ee")},[])
useEffect(() => {
const getArticles = async () => {
const res = await Axios.get(newsurl);
setActicles(res.data.articles);
console.log(res);
};
getArticles();
}, []);
useEffect(() => {
console.log(newsurl)
// Whatever else we want to do after the state ha
s been updated.
}, [newsurl])
//return "https://newsapi.org/v2/top-headlines?country=us&apiKey=c75d8c8ba2f1470bb24817af1ed669ee";}
return (<><Newsnavbar />{articles?.map(({title,description,url,urlToImage,publishedAt,source})=>(
<NewsItem
title={title}
desciption={description}
url={url}
urlToImage={urlToImage}
publishedAt={publishedAt}
source={source.name} />
)) } </>
)
one more things is that when i save the code the page will change to have category but when i refresh it ,it change back to the inital state.Same case when typing the url with no id.May i know how to fix this and the reason behind?
Setting the state in React acts like an async function.
Meaning that the when you set the state and put a console.log right after it, it will likely run before the state has actually finished updating.
You can instead, for example, use a useEffect hook that is dependant on the relevant state in-order to see that the state value actually gets updates as anticipated.
Example:
useEffect(() => {
console.log(newsurl)
// Whatever else we want to do after the state has been updated.
}, [newsurl])
This console.log will run only after the state has finished changing and a render has occurred.
Note: "newsurl" in the example is interchangeable with whatever other state piece you're dealing with.
Check the documentation for more info about this.
setState is an async operation so in the first render both your useEffetcs run when your url is equal to the default value you pass to the useState hook. in the next render your url is changed but the second useEffect is not running anymore because you passed an empty array as it's dependency so it runs just once.
you can rewrite your code like the snippet below to solve the problem.
const [articles, setActicles] = useState([]);
const Id = props.id;
useEffect(() => {
const getArticles = async () => {
const newsurl =
Id === 2
? "https://newsapi.org/v2/top-headlines?country=de&category=business&apiKey=c75d8c8ba2f1470bb24817af1ed669ee"
: "https://newsapi.org/v2/top-headlines?country=us&apiKey=c75d8c8ba2f1470bb24817af1ed669ee";
const res = await Axios.get(newsurl);
setActicles(res.data.articles);
console.log(res);
};
getArticles();
}, []);
I am using firebase and trying to load all my data at the start of the app using this code:
const [books, setBooks] = useState<BookType[]>([]);
const bookCollectionRef = collection(db, "books");
useEffect(() => {
const getBooks = async () => {
const data = await getDocs(bookCollectionRef);
const temp: BookType[] = data.docs.map((doc) => {
const book: BookType = {
//set properties
};
return book;
});
setBooks(temp);
};
getBooks();
}, [bookCollectionRef]);
This useEffect is getting run constantly leading me to believe that I have made an infinite loop. I don't see why this would be happening because I don't think I am updating bookCollectionRef inside the useEffect hook. Is there possibly a problem where firebase collection references constantly get updated? Any ideas help!
From what I can tell it may be that collection(db, "books") returns a new collection reference each time the component rerenders. Any time the component renders (triggered by parent rerendering, props updating, or updating the local books state) the new bookCollectionRef reference triggers the useEffect hook callback and updates the books state, thus triggering a rerender. Rinse and repeat.
If you don't need to reference the collection outside of the useEffect hook then simply omit bookCollectionRef and reference the collection directly. Trigger the useEffect only when the db value updates.
const [books, setBooks] = useState<BookType[]>([]);
useEffect(() => {
const getBooks = async () => {
const data = await getDocs(collection(db, "books"));
const temp: BookType[] = data.docs.map((doc) => {
const book: BookType = {
//set properties
};
return book;
});
setBooks(temp);
};
getBooks();
}, [db]);
If you only need to run the effect once when the component mounts then remove all dependencies, i.e. use an empty dependency array.
I have a useEffect in my component that is waiting for data from the context so that it can set it in state. But its not waiting for the state and is moving on to the next line of code to set isLoading to false.
I'd like it to wait for the data so that I can render the loading.
I tried setting the isFetchingData in the context but I had run into problems where if another component calls it first it would set the isFetchingData state to false.
First call to ReactContext is setting the isLoading sate to false
It is fine for results to come back with no records. The component would render 'No records found'. Therefore, I cannot check the length on state to say if length is zero then keep loading.
Following is my code:
Context
const [activeEmployees, setActiveEmployees] = useState([]);
const [terminatedEmployees, setTerminatedEmployees] = useState([]);
useEffect(() => {
getEmployees()
.then(response => {
/// some code...
setActiveEmployees(response.activeEmployees)
setTerminatedEmployees(response.terminatedEmployees)
});
});
Component
const EmployeesTab = () => {
const { activeEmployees, terminatedEmployees } = useContext(BlipContext);
//Component states
const [isFetchingData, setIsFetchingData] = useState(true);
const [newEmployees, setNewEmployees] = useState([]);
const [oldEmployees, setOldEmployees] = useState([]);
useEffect(() => {
async function getData() {
await setNewEmployees(activeEmployees);
await setOldEmployees(terminatedEmployees);
setIsFetchingData(false);
}
getData();
}, [activeEmployees, terminatedEmployees, isFetchingData]);
if(isFetchingData) {
return <p>'Loading'</p>;
}
return (
// if data is loaded render this
);
};
export default EmployeesTab;
Since you have useState inside your useContext, I don't see the point of storing yet again the activeEmployees in another state.
If you want to have a local loading variable it could something like:
const loading = !(activeEmployees.length && terminatedEmployees.length);
This loading will update whenever getEmployees changes.
And to answer you question, the reason await is not having an effect is because setState is synchronous.
just starting to learn hooks here.
I am getting data from firestore and trying to set it to state using hooks. when I uncomment the line doing so, I get stuck in an infinite loop. no error, but the console goes crazy with logging the state thousands of times.
Let me know if you need more info!
function Lists(props) {
const [lists, setLists] = useState([])
const [loading, setLoading] = useState(true)
useEffect(() => {
const subscriber =
firestore().collection('users').doc(props.user).collection('lists')
.onSnapshot(QuerySnapshot => {
const items = []
QuerySnapshot.forEach(documentSnapshot => {
items.push({
...documentSnapshot.data(),
key: documentSnapshot.id,
});
//setLists(items)
setLoading(false)
console.log(lists)
})
})
// unsubscribe from firestore
return () => subscriber();
})
//rest of func..
this issue happens becauase useEffect gets called over and over again. useEffect is like componentDidMount and componentDidUpdate if you are familiar with React class components.
so whenever you set the state inside the useEffect, you trigger an update, and then, useEffect gets called again, and thus the infinite loop.
to fix this, useEffect accepts a extra argument, which is an array of dependancies, which indicates that this useEffect call should only re-executed whenever a change happens to one of its dependancies. in your case you can provide an empty array, telling react that this useEffect should only be called one time.
useEffect(() => {
const subscriber =
firestore().collection('users').doc(props.user).collection('lists')
.onSnapshot(QuerySnapshot => {
const items = []
QuerySnapshot.forEach(documentSnapshot => {
items.push({
...documentSnapshot.data(),
key: documentSnapshot.id,
});
//setLists(items)
setLoading(false)
console.log(lists)
})
})
// unsubscribe from firestore
return () => subscriber();
}, []) // <------------ the second argument we talked about
I'm fetching data from an API within a file which is the context provider of my React application. However, when I push some data to the API, from a component consuming the context, the data isn't updated in real time, and I have to refresh the page to see it update. How do I make sure it keeps checking the API for new data?
I have added the items state to the dependency array in the useEffect function but this results in the API being constantly called, as opposed to only when the data changes.
ItemsContext.tsx
const [items, setItems] = useState();
useEffect(() => {
const fetchData = async () =>
{
try {
const res = await axios.get(config().URI);
setItems(res.data.items);
} catch (error) {
throw error;
}
};
fetchData();
}, []);