How to fix missing dependency warning when using useEffect React Hook?
./src/components/BusinessesList.js
Line 51: React Hook useEffect has a missing dependency: 'fetchBusinesses'.
Either include it or remove the dependency array react-hooks/exhaustive-deps
It's not a JavaScript/React error, but an ESLint (eslint-plugin-react-hooks) warning.
It's telling you that the hook depends on function fetchBusinesses
, so you should pass it as a dependency.
useEffect(() => {
fetchBusinesses();
}, [fetchBusinesses]);
It could result in invoking the function on every render if the function is declared in a component like:
const Component = () => {
/*...*/
// New function declaration every render
const fetchBusinesses = () => {
fetch('/api/businesses/')
.then(...)
}
useEffect(() => {
fetchBusinesses();
}, [fetchBusinesses]);
/*...*/
}
because every time the function is redeclared with a new reference.
The correct way of doing this stuff is:
const Component = () => {
/*...*/
// Keep the function reference
const fetchBusinesses = useCallback(() => {
fetch('/api/businesses/')
.then(...)
}, [/* Additional dependencies */])
useEffect(() => {
fetchBusinesses();
}, [fetchBusinesses]);
/*...*/
}
Or just define the function in useEffect
.
More: [ESLint] Feedback for 'exhaustive-deps' lint rule #14920
If you aren't using fetchBusinesses method anywhere apart from the effect, you could simply move it into the effect and avoid the warning
useEffect(() => {
const fetchBusinesses = () => {
return fetch("theURL", {method: "GET"}
)
.then(res => normalizeResponseErrors(res))
.then(res => {
return res.json();
})
.then(rcvdBusinesses => {
// some stuff
})
.catch(err => {
// some error handling
});
};
fetchBusinesses();
}, []);
If however you are using fetchBusinesses outside of render, you must note two things
- Is there any issue with you not passing
fetchBusinesses
as a method when it's used during mount with its enclosing closure? - Does your method depend on some variables which it receives from its enclosing closure? This is not the case for you.
- On every render, fetchBusinesses will be re-created and hence passing it to useEffect will cause issues. So first you must memoize fetchBusinesses if you were to pass it to the dependency array.
To sum it up I would say that if you are using fetchBusinesses
outside of useEffect
you can disable the rule using // eslint-disable-next-line react-hooks/exhaustive-deps
otherwise you can move the method inside of useEffect
To disable the rule you would write it like
useEffect(() => {
// other code
...
// eslint-disable-next-line react-hooks/exhaustive-deps
}, [])
There are very good options for state management librariess if you are creating a new app or have enough flexibility. Check out Recoil.
Just for completeness:
1. (Stopped working) Use function as useEffect
callback
useEffect
callbackuseEffect(fetchBusinesses, [])
2. Declare function inside useEffect()
useEffect(() => {
function fetchBusinesses() {
...
}
fetchBusinesses()
}, [])
3. Memoize with useCallback()
In this case, if you have dependencies in your function, you will have to include them in the useCallback
dependencies array and this will trigger the useEffect
again if the function's params change. Besides, it is a lot of boilerplate... So just pass the function directly to useEffect
as in 1. useEffect(fetchBusinesses, [])
.
const fetchBusinesses = useCallback(() => {
...
}, [])
useEffect(() => {
fetchBusinesses()
}, [fetchBusinesses])
4. Function's default argument
As suggested by Behnam Azimi
It's not best practice, but it could be useful in some cases.
useEffect((fetchBusinesses = fetchBusinesses) => {
fetchBusinesses();
}, []);
5. Create a custom hook
Create a custom hook and call it when you need to run function only once. It may be cleaner. You can also return a callback to reset re-run the "initialization" when need.
// customHooks.js
const useInit = (callback, ...args) => {
const [mounted, setMounted] = useState(false)
const resetInit = () => setMounted(false)
useEffect(() => {
if(!mounted) {
setMounted(true);
callback(...args);
}
},[mounted, callback]);
return [resetInit]
}
// Component.js
return ({ fetchBusiness, arg1, arg2, requiresRefetch }) => {
const [resetInit] = useInit(fetchBusiness, arg1, arg2)
useEffect(() => {
resetInit()
}, [requiresRefetch, resetInit]);
6. Disable eslint's warning
Disabling warnings should be your last resort, but when you do, better do it inline and explicitly, because future developers may be confused or create unexpected bugs without knowing linting is off
useEffect(() => {
fetchBusinesses()
}, []) // eslint-disable-line react-hooks/exhaustive-deps
These warnings are very helpful for finding components that do not update consistently: Is it safe to omit functions from the list of dependencies?.
However, if you want to remove the warnings throughout your project, you can add this to your ESLint configuration:
{
"plugins": ["react-hooks"],
"rules": {
"react-hooks/exhaustive-deps": 0
}
}