I am trying to set the state of a variable "workspace", but when I console log the data I get an infinite loop. I am calling the axios "get" function inside of useEffect(), and console logging outside of this loop, so I don't know what is triggering all the re-renders. I have not found an answer to my specific problem in this question. Here's my code:
function WorkspaceDynamic({ match }) {
const [proposals, setProposals] = useState([{}]);
useEffect(() => {
getItems();
});
const getItems = async () => {
const proposalsList = await axios.get(
"http://localhost:5000/api/proposals"
);
setProposals(proposalsList.data);
};
const [workspace, setWorkspace] = useState({});
function findWorkspace() {
proposals.map((workspace) => {
if (workspace._id === match.params.id) {
setWorkspace(workspace);
}
});
}
Does anyone see what might be causing the re-render? Thanks!
The effect hook runs every render cycle, and one without a dependency array will execute its callback every render cycle. If the effect callback updates state, i.e. proposals, then another render cycle is enqueued, thus creating render looping.
If you want to only run effect once when the component mounts then use an empty dependency array.
useEffect(() => {
getItems();
}, []);
If you want it to only run at certain time, like if the match param updates, then include a dependency in the array.
useEffect(() => {
getItems();
}, [match]);
Your use of useEffect is not correct. If you do not include a dependency array, it gets called every time the component renders. As a result your useEffect is called which causes setProposals then it again causes useEffect to run and so on
try this
useEffect(() => {
getItems();
} , []); // an empty array means it will be called once only
I think it's the following: useEffect should have a second param [] to make sure it's executed only once. that is:
useEffect(() => {
getItems();
}, []);
otherwise setProposal will modify the state which will trigger a re-render, which will call useEffect, which will make the async call, which will setProposal, ...
Related
Here is a useEffect hook that I used in reactjs:
Problem: The useEffect calls fetchAllCategories() endlessly. Infact, over 1000 requests until I terminate. I only want it to run on page mount and when I click on the button to change catName state. What could I be doing wrong?
const [catName, setCategories] = useState([]);
const categoryRef = useRef();
useEffect(()=>{
const fetchAllCategories = async () =>{
try{
const res = await axios.get(`${BASE_URL}/category`)
return setCategories(res.data);
}catch(err){
}
}
fetchAllCategories()
}, [catName])
//create new category
const createNewCategory = async ()=>{
const categoryName = {
catName: categoryRef.current.value
}
try{
const response = await axiosPrivate.post(`${BASE_URL}/category`, categoryName, { withCredentials: true,
headers:{authorization: `Bearer ${auth}`}
})
return setCategories([response.data])
}catch(err){
}
}
The button that triggers changes in catName
<button onClick={ createNewCategory} className='button-general'>Create</button>
You trigger the effect to be run on change of catNames, and then change catNames from the effect itself. This results in the endless self-triggering of the effect.
One solution could be to make your effect depend on nothing:
useEffect(() => {
....
}, []);
Thank you all for pointing out the issue to me. Since I now know the issue, I have been able to fix it. All I did was create another state and made the useEffect to depend on it. Then, whenever the button is clicked, I change the state to the opposite of the initial state. This works and doesnt cause endless calls.
If you absolutely need catName as a dependency, this can work for you:
useEffect(() => {
const fetchAllCategories = async () => {
try {
const res = await axios.get(`${BASE_URL}/category`);
return setCategories(res.data);
} catch (err) {}
};
fetchAllCategories();
}, [JSON.stringify(catName)]);
This is happening because you update the catName state inside the useEffect using setCategories(res.data) this keeps triggering your useEffect thus an infinite loop
You programmed it to run endlessly.
REASON
See, this React hook useEffect has two parameters:
Effect, the callback function which is called whenever the component renders.
List of Dependencies on which the useEffect hook depends and re-renders if any such dependency is updated.
Now, in your case, you've passed catName as a dependency, whose state is updated when the button is clicked. This causes useEffect to call the callback function which calls fetchAllCategories() which also update catName. And this causes an endless loop.
SOLUTION
Just remove the dependency from useEffect as:
useEffect(() {
...
}, []);
Now, updating catName won't cause the effect (The Callback function) to be called endlessly.
function Reply({ id, user }) {
const [data, setData] = useState([]);
const [replyText, setReplyText] = useState("");
useEffect(() => {
async function fetchData() {
const response = await _axios.get("/reply/" + id);
setData(response.data);
}
fetchData();
}, [data]); <---- ** problem ** with data(dependency),
infinite request(call) fetchData()
...
}
what's the reason for infinite loop if there's a dependency.
as far as i know, when dependency(data) change, re-render.
but useEffect keep asking for data(axios.get(~~)).
if i leave a comment, i can see normally the latest comments, but the network tab(in develop tools) keeps asking for data(304 Not Modified, under image)
There's an infinite loop because that code says "If data changes, request information from the server and change data." The second half of that changes data, which triggers the first half again.
You're not using data in the callback, so it shouldn't be a dependency. Just remove it:
useEffect(() => {
async function fetchData() {
const response = await _axios.get("/reply/" + id);
setData(response.data);
}
fetchData();
}, []);
// ^^−−−−−−−−−− don't put `data` here
That gives you a blank dependency array, which will run the effect only when the component first mounts. (If you want to run it again after mount, use a different state member for that, or define fetchData outside the effect and use it both in the effect and at the other time you want to fetch data.)
Side note: Nothing in your code is handling rejections from your fetchData function, which will cause "unhandled rejection" errors. You'll want to hook up a rejection handler to report or suppress the error.
You are using setData after the response which causes the data to change and hence the useEffect(() => {<>your code<>} ,[data]) to fire again.
use useEffect(() => {<>your code<>},[]) if you want to execute the AJAX call only once after component mounting
or
use useEffect(() => {<>your code<>}) without the dependency if you want to execute the AJAX call after the component mount and after every update
Dependencies argument of useEffect is useEffect(callback, dependencies)
Let's explore side effects and runs:
Not provided: the side-effect runs after every rendering.
import { useEffect } from 'react';
function MyComponent() {
useEffect(() => {
// Runs after EVERY rendering
});
}
An empty array []: the side-effect runs once after the initial rendering.
import { useEffect } from 'react';
function MyComponent() {
useEffect(() => {
// Runs ONCE after initial rendering
}, []);
}
Has props or state values [prop1, prop2, ..., state1, state2]: the side-effect runs only when any dependency value changes.
import { useEffect, useState } from 'react';
function MyComponent({ prop }) {
const [state, setState] = useState('');
useEffect(() => {
// Runs ONCE after initial rendering
// and after every rendering ONLY IF `prop` or `state` changes
}, [prop, state]);
}
I Got Stuck in an infinite loop in react.js. How to resolve this?
useEffect(() => {
fetch("https://react-http-d55a9-default-rtdb.firebaseio.com/todo.json")
.then((response) => {
return response.json();
})
.then((data) => {
console.log(data);
setUsersList((prev) => [...prev]); //cause of infinite loop
});
}, [usersList]);
You are having an infinite loop because your useEffect array of dependencies has usersList on it and at the same time you are updating this variable inside your useEffect function. So your useEffect runs when the component mounts which updates your usersList which makes the useEffect run again which again updates your usersList which makes it run again and so on...
To fix this, remove usersList from the array of dependencies and have an empty array instead: []. If you do this your useEffect will run once, when your component mounts.
The dependency list passed to useEffect determines when the effect should run again. The infinite loop is happening because this effect causes usersList to change, which triggers the effect to run again.
Since this effect doesn't use any other variables, it doesn't need anything in its dependency list:
useEffect(() => {
fetch(...)
// ...
}, []); // leave this empty, so the effect only runs when the component mounts
If your URL depended on a prop or something else, then you want it in the dependency list:
useEffect(() => {
fetch(`https://example.com/todo/${props.id}`)
.then(...)
// Since the URL depends on the id prop, the effect should re-run if it changes
}, [props.id]);
According to question asked, you want the userList to be watched everytime it updates. What we can do is define one more state variable as mentioned in the code as isFetched or if you are using redux you can put that over there, because if we just watch the userList variable then it caughts up in infinite loop as setting the userList is happening in useEffect itself. With the help of isFetched, we can manage when to call the api and whenever the flag is false it calls the api.
Right now in the code i have put one more state variable as setCount, as i didn't know how many times you want to call your api. So you can put your condition there and stop the call when your condition satisfies.
function App() {
const [userList, setUserList] = useState([]);
const [isFetched, setIsFetched] = useState(false);
const [, setCount] = useState(3);
const callApiPending = useCallback(()=>{
fetch("https://react-http-d55a9-default-rtdb.firebaseio.com/todo.json")
.then((response) => response.json())
.then((json) => {
setUserList((prev) => [...prev, ...json]);
setCount((cnt) => {
if(cnt - 1 === 0){
setIsFetched(true);
}
return cnt - 1;
});
});
}, []);
useEffect(() => {
if (!isFetched) {
callApiPending();
}
}, [isFetched, userList, callApiPending]);
return <div>Executing....</div>;
}
You ran fetch if usersList changes. Even if userList content is the same as previous content, javascript interpret as it changed. Try this one.
[1,2,3] == [1,2,3]
may return false. You can use a flag which is used to check whether or not to get data instead of using array.
I have a problem when using the useEffect hook, it is generating an infinite loop.
I have a list that is loaded as soon as the page is assembled and should also be updated when a new record is found in "developers" state.
See the code:
const [developers, setDevelopers] = useState<DevelopersData[]>([]);
const getDevelopers = async () => {
await api.get('/developers').then(response => {
setDevelopers(response.data);
});
};
// This way, the loop does not happen
useEffect(() => {
getDevelopers();
}, []);
// This way, infinte loop
useEffect(() => {
getDevelopers();
}, [developers]);
console.log(developers)
If I remove the developer dependency on the second parameter of useEffect, the loop does not happen, however, the list is not updated when a new record is found. If I insert "developers" in the second parameter of useEffect, the list is updated automatically, however, it goes into an infinite loop.
What am I doing wrong?
complete code (with component): https://gist.github.com/fredarend/c571d2b2fd88c734997a757bac6ab766
Print:
The dependencies for useEffect use reference equality, not deep equality. (If you need deep equality comparison for some reason, take a look at use-deep-compare-effect.)
The API call always returns a new array object, so its reference/identity is not the same as it was earlier, triggering useEffect to fire the effect again, etc.
Given that nothing else ever calls setDevelopers, i.e. there's no way for developers to change unless it was from the API call triggered by the effect, there's really no actual need to have developers as a dependency to useEffect; you can just have an empty array as deps: useEffect(() => ..., []). The effect will only be called exactly once.
EDIT: Following the comment clarification,
I register a developer in the form on the left [...] I would like the list to be updated as soon as a new dev is registered.
This is one way to do things:
The idea here is that developers is only ever automatically loaded on component mount. When the user adds a new developer via the AddDeveloperForm, we opportunistically update the local developers state while we're posting the new developer to the backend. Whether or not posting fails, we reload the list from the backend to ensure we have the freshest real state.
const DevList: React.FC = () => {
const [developers, setDevelopers] = useState<DevelopersData[]>([]);
const getDevelopers = useCallback(async () => {
await api.get("/developers").then((response) => {
setDevelopers(response.data);
});
}, [setDevelopers]);
useEffect(() => {
getDevelopers();
}, [getDevelopers]);
const onAddDeveloper = useCallback(
async (newDeveloper) => {
const newDevelopers = developers.concat([newDeveloper]);
setDevelopers(newDevelopers);
try {
await postNewDeveloperToAPI(newDeveloper); // TODO: Implement me
} catch (e) {
alert("Oops, failed posting developer information...");
}
getDevelopers();
},
[developers],
);
return (
<>
<AddDeveloperForm onAddDeveloper={onAddDeveloper} />
<DeveloperList developers={developers} />
</>
);
};
The problem is that your getDevelopers function, calls your setDevelopers function, which updates your developers variable. When your developers variable is updated, it triggers the useEffect function
useEffect(() => {
getDevelopers();
}, [developers]);
because developers is one of the dependencies passed to it and the process starts over.
Every time a variable within the array, which is passed as the second argument to useEffect, gets updated, the useEffect function gets triggered
Use an empty array [] in the second parameter of the useEffect.
This causes the code inside to run only on mount of the parent component.
useEffect(() => {
getDevelopers();
}, []);
I am trying to build a redux process with react hooks, the code below is that I want to simulate a ComponentDidMount function with a getUsers(redux action) call in it which is a http request to fetch data.
The first version was like this
const { state, actions } = useContext(StoreContext);
const { getUsers } = actions;
useEffect(() => {
getUsers(); // React Hook useEffect has a missing dependency: 'getUsers'.
}, []);
but I got a linting warning "React Hook useEffect has a missing dependency: 'getUsers'. Either include it or remove the dependency array" in useEffect,
and then I added getUsers to dependency array, but got infinite loop there
useEffect(() => {
getUsers();
}, [getUsers])
Now I find a solution by using useRef
const fetchData = useRef(getUsers);
useEffect(() => {
fetchData.current();
}, []);
Not sure if this is the right way to do this, but it did solve the linting and the infinite loop (temporarily?)
My question is:
In the second version of the code, what exactly caused the infinite loop? does getUsers in dependency array changed after every render?
Your function have dependencies and React deems it unsafe not to list the dependencies. Say your function is depending on a property called users. Listing explicitly the implicit dependencies in the dependencies array won't work:
useEffect(() => {
getUsers();
}, [users]); // won't work
However, React says that the recommended way to fix this is to move the function inside the useEffect() function. This way, the warning won't say that it's missing a getUsers dependency, rather the dependency/ies that getUsers depends on.
function Example({ users }) {
useEffect(() => {
// we moved getUsers inside useEffect
function getUsers() {
console.log(users);
}
getUsers();
}, []); // users dependency missing
}
So you can then specify the users dependency:
useEffect(() => {
function getUsers() {
console.log(users);
}
getUsers();
}, [users]); // OK
However, you're getting that function from the props, it's not defined in your component.
What to do then? The solution to your problem would be to memoize your function.
useCallback will return a memoized version of the callback that only changes if one of the dependencies has changed. This is useful when passing callbacks to optimized child components that rely on reference equality to prevent unnecessary renders (e.g. shouldComponentUpdate).
You can't memoize it within your component as there will be the same warning:
const memoizedGetUsers = useCallback(
() => {
getUsers();
},
[], // same warning, missing the getUsers dependency
);
The solution is to memoize it right where the getUsers is defined and you will be then be able to list the dependencies:
// wrap getUsers inside useCallback
const getUsers = useCallback(
() => {
//getUsers' implementation using users
console.log(users);
},
[users], // OK
);
And in your component, you'll be able to do:
const { getUsers } = actions; // the memoized version
useEffect(() => {
getUsers();
}, [getUsers]); // it is now safe to set getUsers as a dependency
As to the reason why there was an infinite loop and why useRef worked. I'm guessing your function causes a rerender and at each iteration, getUsers was recreated which ends up in an endless loop. useRef returns an object { current: ... } and the difference between using useRef and creating this object { current: ... } yourself is that useRef returns the same object and doesn't create another one. So you were propbably using the same function.
You should declare getUsers inside useEffect it it's the only place you call getUsers
useEffect(() => {
const { getUsers } = props;
getUsers();
}, []);
By my information on React hooks the job of the second parameter is to be used as a variable of comparision as it would have been in shouldComponentUpdate.
By my understanding of the question getUsers is a function and not a variable that might changeon some condition and hence the infinite loop. Try passing a props that would change after getUsers is called.
import React, { useState,useEffect } from 'react';
function Input({getInputElement}) {
let [todoName, setTodoName] = useState('');
useEffect (() => {
getInputElement(todoName);
},[todoName]);
return (
<div>
<input id={'itemNameInput'} onChange={(e) => setTodoName(e.target.value)} value={todoName} />
</div>
);
}
export default Input;
useEffect : useEffect is a combination of componentDidMount, componentDidUpdate and shouldComponentUpdate. While componentDidMount runs after first render and componentDidUpdate runs after every update, useEffect runs after every render and thus covers both the scenarios. The second optional param to useEffect is the check for shouldComponentUpdate in our case [todoName].This basically checks if todoName has changed after rerender then only do whatever is inside useEffect function.
Hope this helps!