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Infinite Loop while using react hook

I'm learning react for past few days and while using useEffect hook i'm getting infite loop over setting my state variable.
Can anyone tell me what's going on and how to overcome this
Here's my code
import React, { useState, useEffect } from "react";
import axios from "axios";
const TodoEntry = () => {
const [todos, setTodos] = useState('');
useEffect(() => {
axios.get('http://localhost:5000/api/todos')
.then(res => { setTodos(res.data); console.log(todos) })
.catch(err => console.log(err))
},[todos]);
return (
<div>
<h1>Todo App</h1>
</div>
);
};
export default TodoEntry;

Couple of problems in your code:
Since getTodos function is a dependency of useEffect hook, every time state updates, new getTodos function is created which then triggers the useEffect hook.
You don't need to chain then function when using async-await syntax. You can just await the result of axios.get(...).
To fix the first problem of infinite loop, use one of the following options:
Wrap the getTodos function in useCallback hook. For details, see useCallback.
Since, getTodos function calls displayTodos, you will need to wrap it in useCallback hook and add displayTodos in the dependency array of useCallback hook that wraps getTodos function. In my opinion, it is better to just remove the displayTodos function and update the state inside getTodos function
const getTodos = useCallback(async () => {
try {
const res = await axios.get('http://localhost:5000/api/todos')
setTodos(res.data);
} catch(err) {
console.log(err);
}
}, [setTodos]);
Demo
Put the code inside getTodos inside useEffect hook and remove the getTodos function.
useEffect(() => {
axios.get("http://localhost:5000/api/todos")
.then(res => setTodos(res.data))
.catch(err => console.log(err));
}, [setTodos]);
Demo

This is because the dependency list for your useEffect call is a function. You probably meant to add the todos data itself.
useEffect(() => {
getTodos();
},[todos]);

React Hook useEffect has a missing dependency, using Redux

Should I ignore 'React Hook useEffect has a missing dependency' warning?
Usually when I am getting data from an API this is what I do:
const Component = () => {
const [data,setData] = useState([]);
const getData = () => {
//Getting data and set data code...
}
useEffect(()=>{
getData();
},[]);
}
and recently I am trying out use redux to do the same thing(getting data from API) and I got this 'React Hook useEffect has a missing dependency' warning...
action:
import {GET_POSTS} from './types';
const getPosts = () => (dispatch) => {
const url = 'https://jsonplaceholder.typicode.com/posts';
fetch(url)
.then(res => res.json())
.then(data => {
dispatch({
type: GET_POSTS,
payload: data
});
});
}
export default getPosts;
reducer:
import {GET_POSTS} from '../actions/types';
const initialState = {
posts: []
}
const postsReducer = (state = initialState, action) => {
switch(action.type){
case GET_POSTS:
return {
...state,
posts: action.payload
}
default:
return state;
}
}
export default postsReducer;
app.js:
import React, {useEffect} from 'react';
import {connect} from 'react-redux';
import Hello from './components/Hello';
import getPost from './actions/postsAction';
import './App.css';
const App = ({getPost, dispatch}) => {
useEffect(() => {
getPost();
},[]);
return (
<div className='App'>
<Hello/>
</div>
);
};
const mapdispatchtoprops = (dispatch) => ({
dispatch,
getPost: () => {
dispatch(getPost());
}
});
export default connect(null, mapdispatchtoprops)(App);
Is there a way to fix this problem, I have tried to put dispatch inside the useEffect array but the warning still shows, like this:
useEffect(() => {
getPost();
},[dispatch]);
This is the full warning: React Hook useEffect has a missing dependency: 'getPost'. Either include it or remove the dependency array react-hooks/exhaustive-deps
Tried to remove the useEffect array but I'll get infinite loop, it'll just keeps getting the data from the api(I only need it to run once).
Should I ignore the warning? if not, whats the best practice way to handle this problem?
I never got this kind of warning before when I left the useEffect array empty but got it recently, why?

The error message is telling you what you to do. Just add getData to the dependencies array like so: [dispatch, getData]. Anything external you reference within your useEffect (like a function) should be part of the dependency list so it can trigger the effect whenever the value changes. In your case it likely won't, but React is warning you just to be safe. Hope that helps!

You may want to start thinking from a different perspective. You are apparently trying to do side effect of loading data after component got rendered. So just inject your data via redux or propagation props from parent and remove array altogether. I.e.
const Component = ({posts}) => {
const getData = () => {
//Getting data and set data code...
}
useEffect(() => {
if (!posts) {
getData();
}
});
....
}
Your posts will be loaded once and useEffect's function should only care about posts is there or not.

React-Redux + Redux-Thunk on functional component. Update UI after data is fetched from API

I have a functional component that fetches data from an api using redux.
const useFetching = (someFetchActionCreator) => {
const dispatch = useDispatch();
useEffect(() => {
dispatch(someFetchActionCreator());
}, [])
}
The component:
export function Trips(props) {
const trips = useSelector(state => state.trips);
useFetching(fetchTrips)
...
...
}
The thunk:
export const fetchTrips = () => (dispatch) =>
axios.get("/api/v1/trips")
.then(response => dispatch(addTrips(response.data)))
export const addTrips = trips => ({
type: ADD_TRIPS,
payload: trips
})
The reducer:
function tripsReducer(state = INITIAL_STATE, action) {
console.log(action)
if (action.type === ADD_TRIPS) {
return Object.assign({}, state, {
trips: state.trips.concat(action.payload)
});
}
return state
}
My reducer is called. How can I update the UI after the fetched data have been dispatched? My render is not called again.

1st option: Using hooks
You are actually using React and react-redux hooks. Make sure you use the object trips later in your component. Here is a sample using your code:
import React, { useEffect } from 'react';
import { useSelector, useDispatch } from 'react-redux';
import { fetchTrips } from '../tripsActions';
const useFetching = (someFetchActionCreator) => {
const dispatch = useDispatch();
useEffect(() => {
dispatch(someFetchActionCreator());
}, []);
}
export function Trips(props) {
const trips = useSelector(state => state.trips);
useFetching(fetchTrips);
return (
<div>
<p>Total trips: {trips.length}</p>
</div>
);
}
2nd option: Using connect
This was the way to connect to the Redux store state before they introduced the hooks.
As you are using react-redux this can be easily done by using the connect() function. You should also provide a mapStateToProps() function to select the part of the data from the store that your component needs and a mapDispatchToProps() function to have access to the actions to be dispatched.
This is how your Trips component would look like with this approach:
import React from 'react';
import { connect } from 'react-redux';
import { fetchTrips } from '../tripsActions';
const mapStateToProps = (state) => {
return {
// will be available as props.trips
trips: state.trips
}
}
const mapDispatchToProps = (dispatch) => {
return {
// will be available as props.fetch()
fetch: () => dispatch(fetchTrips)
}
}
const function Trips(props) {
this.props.fetch();
// some other code. Example:
return (
<div>
<p>Total trips: {this.props.trips.length}</p>
</div>
);
}
export default connect(mapStateToProps)(Trips);
mapStateToProps() receives the Redux store state and returns an object whose fields will be available as props in your component. As you already use props.trips I simply mapped that field to the updated value of the Redux state's trips field.
The call to connect() with your component gives you a connected component. And that latter should be exported rather than the original component. It will not create another component so you will continue to use the Trips component normally.
Now your component will be re-rendered as its props are being updated.
You can have a look at the react-redux documentation to better understand the use of connect() and mapStateToProps() and mapDispatchToProps() functions.

You can do it easily like that:
import React, {
useCallback, useEffect
} from 'react';
import {
useSelector, useDispatch
} from 'react-redux';
// ../ducks for example
import { fetchTrips } from '../ducks';
const function Trips(props) {
const dispatch = useDispatch();
useEffect(() => {
fetchTripsHandler();
}, []);
const fetchTripsHandler = useCallback(
() => dispatch(fetchTrips()),
[]
);
const { trips } = useSelector(state => ({
trips: state.trips
}));
// your other component code
}
With useSelector from react-redux you can not use connect, mapStateToProps and mapDispatchToProps.
After that, your component will be connected to the Store.
Here is more information about react-redux hooks.

How can we use Redux dispatch() into useEffect? cause I am getting error [duplicate]

My folder structure:
|--App
|--Components
|--PageA.js
|--PageB.js
|--PageC.js
|--common-effects
|--useFetching.js
I am refactoring my code to fetch data from API, using react hooks.
I want to dispatch an action from useEffect in useFetching.js that is intercepted by saga middleware. The action should be dispatched only when the components(PageA, PageB, PageC) mount.
I am using redux, react-redux and redux-saga.
PageA.js:
function(props) {
useFetching(actionParams)
//....//
}
Similar code for PageB and PageC components.
I have abstracted the reusable code to fetch data in useFetching Custom hook.
useFetching.js
const useFetching = actionArgs => {
useEffect( () => {
store.dispatch(action(actionArgs)); // does not work
})
}
I don't know how to access redux dispatch in useFetching. I tried it with useReducer effect, but the sagas missed the action.

Version using react-redux hooks:
You can even cut out the connect function completely by using useDispatch from react-redux:
export default function MyComponent() {
useFetching(fetchSomething);
return <div>Doing some fetching!</div>
}
with your custom hook
import { useDispatch } from 'react-redux';
const useFetching = (someFetchActionCreator) => {
const dispatch = useDispatch();
useEffect(() => {
dispatch(someFetchActionCreator());
}, [])
}
Edit: removed dispatch from custom hook as suggested by #yonga-springfield
Note: React guarantees that dispatch function identity is stable and won’t change on re-renders. This is why it’s safe to omit from the useEffect or useCallback dependency list.

You would need to pass either bound action creators or a reference to dispatch to your hook. These would come from a connected component, same as you would normally use React-Redux:
function MyComponent(props) {
useFetching(props.fetchSomething);
return <div>Doing some fetching!</div>
}
const mapDispatch = {
fetchSomething
};
export default connect(null, mapDispatch)(MyComponent);
The hook should then call the bound action creator in the effect, which will dispatch the action accordingly.
Also, note that your current hook will re-run the effect every time the component is re-rendered, rather than just the first time. You'd need to modify the hook like this:
const useFetching = someFetchActionCreator => {
useEffect( () => {
someFetchActionCreator();
}, [])
}

This is just to bring some optimization to #Alex Hans' answer.
As per the documentation here. A custom Hook is a JavaScript function whose name starts with ”use” and that may call other Hooks.
With this in mind, we need not send a reference to the dispatch function to the useFetching hook as a parameter but rather, simply not send it and rather simply use it from within the useFetching hook with the appropriate imports.
Here's an excerpt of what I mean.
import { useDispatch } from 'react-redux';
const useFetching = (someFetchActionCreator) => {
const dispatch = useDispatch()
useEffect(() => {
dispatch(someFetchActionCreator());
}, [])
}
I can't ascertain this example will fit without errors in your codebase in your case but just trying to explain the idea/concept behind this post.
Hope this helps any future comer.

Alex Hans right decision with dispatch, but to eliminate request loops to api you can specify the dependence on dispatch ( I used Redux Toolkit )
import React, { useEffect } from 'react'
import { useDispatch } from 'react-redux'
import axios from 'axios'
import { getItemsStart, getItemsSuccess, getItemsFailure } from '../features/itemsSlice'
const fetchItems = () => async dispatch => {
try {
dispatch(getItemsStart());
const { data } = await axios.get('url/api')
dispatch(getItemsSuccess(data))
} catch (error) {
dispatch(getItemsFailure(error))
}
}
const PageA = () => {
const dispatch = useDispatch()
const { items } = useSelector(state => state.dataSlice)
useEffect(() => {
dispatch(fetchItems())
}, [dispatch])
return (
<ul>
{items.map(item => <li>{item.name}</li>}
</ul>
)
}
export default PageA
it is important to passed dependency parameter of dispatch in the useEffect(() => {...}, [dispatch])

useEffect(() => {
fetchData();
}, []);
async function fetchData() {
try {
await Auth.currentSession();
userHasAuthenticated(true);
} catch (e) {
if (e !== "No current user") {
alert(e);
}
}
dispatch(authentication({ type: "SET_AUTHING", payload: false }));
}

React Hooks and ActionCable

Trying to get along with React new Hooks and ActionCable, but stuck with the problem that I can't get the right data in Rails when trying to send state.
I've tried to use send() method immediately after doing setState() and send my updated data, but for some reason, the data which received on the Rails part is old.
For example, if I put "Example" to the input I'll see "{"data"=>"Exampl"} on the Rails side. I suppose the data update the state later than my request goes.
If I send() value from e.target.value everything works fine
Therefore I've tried to use new useEffect() hook and send data there. But I get only data when rendering the page. Afterward, I don't get anything and sometimes get error RuntimeError - Unable to find subscription with an identifier. Seems like effect hook sends data too early or something.
I'm pretty new to Hooks and WebSockets. Would love to get any help here. I can share Rails code, but there is only a receiver and nothing else.
First exmaple:
import React, { useState, useEffect } from "react"
import ActionCable from 'actioncable'
function Component(props) {
const [data, setData] = useState("");
const cable = ActionCable.createConsumer('ws://localhost:3000/cable');
const sub = cable.subscriptions.create('DataChannel');
const handleChange = (e) => {
setData(e.target.value)
sub.send({ data });
}
return (
<input value={data} onChange={handleChange}/>
)
}
Tried to useEffect and move send() there:
useEffect(() => {
sub.send({ data });
}, [data]);
I'd love to find a way to correctly use React and ActionCable. And use hooks if it's possible.

I was trying an approach similar to Oleg's but I could not setChannel inside the action cable create subscription callback. I had to setChannel outside of the callback but within the useEffect hook. Below is the solution that worked for me.
create consumer in index.js and provide the consumer through Context to App.
index.js
import React, { createContext } from 'react'
import actionCable from 'actioncable'
... omitted other imports
const CableApp = {}
CableApp.cable = actionCable.createConsumer('ws://localhost:3000/cable')
export const ActionCableContext = createContext()
ReactDOM.render(
<Router>
... omitted other providers
<ActionCableContext.Provider value={CableApp.cable}>
<App />
</ActionCableContext.Provider>
</Router>,
document.getElementById('root')
)
Use the cable context in your child component and create subscription in useEffect hooks; unsubscribe in clean up
import React, { useState, useEffect, useContext } from 'react'
import { useParams } from 'react-router-dom'
... omitted code
const [channel, setChannel] = useState(null)
const { id } = useParams()
const cable = useContext(ActionCableContext)
useEffect(() => {
const channel = cable.subscriptions.create(
{
channel: 'MessagesChannel',
id: id,
},
{
received: (data) => {
receiveMessage(data)
},
}
)
setChannel(channel)
return () => {
channel.unsubscribe()
}
}, [id])
const sendMessage = (content) => {
channel.send(content)
}

You can register your cable at root component like that:
import actionCable from 'actioncable';
(function() {
window.CableApp || (window.CableApp = {});
CableApp.cable = actionCable.createConsumer('ws://localhost:3000/cable')
}).call(this);`
so it will be available as global variable;
and then in any component where you want to create channel and send data:
const [channel, setChannel] = useState(null);
useEffect(() => {
CableApp.cable.subscriptions.create(
{
channel: 'YourChannelName',
},
{
initialized() {
setChannel(this)
},
},
);
}, []);
return <button onClick={() => channel.send(some_data)} >Send counter</button>

Your problem is here:
const handleChange = (e) => {
setData(e.target.value)
sub.send({ data });
}
setData is like setState in that the state is only updated after the render i.e. after the function has exited. You are sending the current data not the new data. Try this:
const handleChange = (e) => {
const newData = e.target.value;
setData(newData)
sub.send({ data: newData });
}