I am working on a project, which is a django project with REACT as the frontend. For the homepage, there is a useState variable ('room_code') that is used. The setstate variable is set_room_code. So, i have an async function that fetches the room code from an api and then the idea is to use the set_room_code hook. But this is just not working. The issue is with the set_room_code as the code works if i simply remove it. I have tried to search up ideas but i am short on it. Any input would be appreciated.
useEffect( () => {
let fetch_code = async () => {
const response = await fetch('/api/user-room');
const data = await response.json();
console.log('hi');
console.log(data.room_code);
console.log('bhao');
set_room_code(data.room_code);
};
fetch_code();
console.log(hi);
}, []);
I have tried using an extra useEffect hook but that doesnt work as well
A few things, first its best practice to name the useState variable
const [roomCode, setRoomCode] = useState();
FYI.
Now as to your question--
useEffect( () => {
let fetch_code = () => {
fetch('/api/user-room').then((data) => {
setRoomCode(data.room_code);
console.log(data.room_code);
return response.json();
});
};
fetch_code();
console.log("this should show your RoomCode", roomCode)
}, [roomCode]);
Related
I am newbie in React Native and I am trying to store and get an array with AsyncStorage in ReactNative.
I have two problems.
First, I do not know why but when I storage data, it only works the second time but I am calling first the set of useState.
const handleAddTask = () => {
Keyboard.dismiss();
setTaskItems([...taskItems, task]);
storeData(taskItems);
};
Second, how can I call the getData function to get all the data and show it? Are there something like .onInit, .onInitialize... in ReactNative? Here is my full code
const [task, setTask] = useState();
const [taskItems, setTaskItems] = useState([]);
const handleAddTask = () => {
Keyboard.dismiss();
setTaskItems([...taskItems, task]);
storeData(taskItems);
};
const completeTask = (index) => {
var itemsCopy = [...taskItems];
itemsCopy.splice(index, 1);
setTaskItems(itemsCopy);
storeData(taskItems);
}
const storeData = async (value) => {
try {
await AsyncStorage.setItem('#tasks', JSON.stringify(value))
console.log('store', JSON.stringify(taskItems));
} catch (e) {
console.log('error');
}
}
const getData = async () => {
try {
const value = await AsyncStorage.getItem('#tasks')
if(value !== null) {
console.log('get', JSON.parse(value));
}
} catch(e) {
console.log('error get');
}
}
Updating state in React is not super intuitive. It's not asynchronous, and can't be awaited. However, it's not done immediately, either - it gets put into a queue which React optimizes according to its own spec.
That's why BYIRINGIRO Emmanuel's answer is correct, and is the easiest way to work with state inside functions. If you have a state update you need to pass to more than one place, set it to a variable inside your function, and use that.
If you need to react to state updates inside your component, use the useEffect hook, and add the state variable to its dependency array. The function in your useEffect will then run whenever the state variable changes.
Even if you're update state setTaskItems([...taskItems, task]) before save new data in local storage, storeData(taskItems) executed before state updated and save old state data.
Refactor handleAddTask as below.
const handleAddTask = () => {
Keyboard.dismiss();
const newTaskItems = [...taskItems, task]
setTaskItems(newTaskItems);
storeData(newTaskItems);
};
While working with react useEffect hook, most of the example I came across in case of calling api data in useEffect hook for initiate the component is, calling api directly inside useEffce hook.
For instance,
useEffect(() => {
async function(){
const res = await axios.get(`https://jsonplaceholder.typicode.com/${query}`);
setData(res.data)
}
}, []);
But what about fetch data outside the hook with a method ? For instance,
const getData = () => {
async function(){
const res = await axios.get(`https://jsonplaceholder.typicode.com/${query}`);
setData(res.data)
}
useEffect(() => {
getData(); // here eslint shows an warning "Promise returned from setData is ignored"
}, [])
is there any specific reason for avoiding second example. If not what's the proper way to call api call function in useEffect hook with proper cleanup ?
In React component file
useEffect(() => {
loadData(query).then(setData)
}, [query])
crate another service file to serve data from API
in service file
export const loadData = async query => {
const res = axios.get(`https://jsonplaceholder.typicode.com/${query}`);
return res.data;
// You can put this API call in try catch to handle API errors
};
Creating a separate function for calling an api is a perfect example of loading data in useEffect. You can give it parameters if you would have a paginated endpoint and call it multiple times or add polling to the page to load the data by interval. I can only see benefits by creating a function for this.
useEffect(() => { fetch("./product.JSON") .then(res => res.json()) .then(data => setProducts(data)) }, [])
I want to fetch some data from a database, and depending on the user the returned data should differ. The way i tried it, was by passing the userid as a query. The id is stored as a redux state. The problem is, that it takes some time before the redux state is available. Ive tried fixing this with if statements, and rerunning the useEffect everytime the auth state is updated. This doesn't work.
I want to fetch, when the redux state auth.user.id is available. Which it is like .1 sec after the initial load.
Here is my code:
const auth = useSelector((state) => state.auth);
useEffect(async () => {
if (auth.token.length > 0) {
const res = await getData(`calendar/?userId=${auth.user.id}`);
setLessons(res.lessons);
setEvents(res.events);
}
}, [auth, date]);
I believe useEffect is already asynchronous, so you don't need to use the async keyword in the anonymous callback. You can create the async function for that logic elsewhere and call it within the useEffect.
Similarly, you could put in self calling async function within your useEffect as such:
useEffect(() => {
(async () => {
if (auth.token.length) {
try {
const res = await getData(`calendar/?userId=${auth.user.id}`);
setLessons(res.lessons);
setEvents(res.events);
}catch (err) {console.log(err);}
}
})();
}, [auth, date]);
I think this link may be helpful:
React Hook Warnings for async function in useEffect: useEffect function must return a cleanup function or nothing
So with the basic understanding, I assume that you need to call the API whenever userId is available. try the below useEffect
useEffect(async () => {
// check user id is available here
if (auth.user && auth.user.id) {
const res = await getData(`calendar/?userId=${auth.user.id}`);
setLessons(res.lessons);
setEvents(res.events);
// some other statements
}
}, [auth, date]);
I have no issues fetching the data from an API using useEffect. That works fine.
The problem is that I need to apply some processing to the data before I actually render it out (in this case, I need to shuffle the array that I receive).
I tried a million different ways, but I just can't find the right place to write that logic. Basically, it won't work anywhere.
What is the right way of going about this?
you can do everything with data before setState.
is useEffect when you fetched data from Api, shuffle it and then do setState.
little example:
useEffect(() => {
axios.get("http://example.com/data").then(response => {
const data = shuffle(response.data);
setState(data);
})
});
useEffect(() => {
const fetchData = async () => {
await axios.get("http://example.com/data").then(response => {
const data = shuffle(response.data);
setState(data);
});
};
fetchData();
return () => {
// Clean up func
}
}, []); //[] will prevent infinite API calling.
I'm beginner with React. I have 2 different cases where I'm using React Hooks which I cannot receive the data from my local API properly.
Case 1:
export const RegisterT = () => {
const [test, setTest] = useState()
const addrState = {}
axios.get('http://127.0.0.1:3333/states', { addrState })
.then(res => {
setTest(res.data)
console.log(test)
})
...
}
It works with the state test displaying correctly the content from the API but I don't know why/how the Axios continues calling the API infinity - endless. (Ps: the very first call it returns undefined, then the next ones it works) What am I doing wrong?
To fix this I've tried to use useEffect like this (Case 2):
export const RegisterT = () => {
const [test, setTest] = useState()
const addrState = {}
useEffect(() => {
axios.get('http://127.0.0.1:3333/states', { addrState })
.then(res => {
setTest(res.data)
console.log(test);
})
}, [])
...
}
Now the Axios works only once but no data is coming from the API. Maybe I should use async/wait for this case but I cannot make it work. Does anyone know how to fix that (Case 1 or/and Case 2)?
Thanks.
Updating the state is an asynchronous operation. So the state is not really updated until the next time the component gets rendered. If you want to capture the correct state, you can either console.log(res.data) or wrap that inside the useEffect hook with test as dependency.
export const RegisterT = () => {
const [test, setTest] = useState()
const addrState = {}
// effect only runs when component is mounted
useEffect(() => {
axios.get('http://127.0.0.1:3333/states', { addrState })
.then(res => {
setTest(res.data);
});
}, []);
// effect runs whenever value of test changes
useEffect(() => {
console.log(test);
}, [test]);
}
That way it is guaranteed that the console.log runs when the value of test is updated.
Also the reason the API request is invoked once is you have not mentioned anything in the dependency array. [] empty dependency array runs the effect when the component is mounted for the first time.
async/await is just a wrapper around Promise object. So they would behave similarly.
The solution with useEffect is good. If you don't use it each render will call the request. This is the same if you put there console.log with any information. The reason why you don't see the data in the useEffect is that the value of the state is not updated in current render but in the next which is called by setter of the state. Move the console.log(test); after useEffect to see the data. On init it will be undefined but in the next render, it should contain the data from the request.