Develop Reference

Only one item is added in state when adding multiple with multiple setState calls

For learning purposes, I'm creating an e-shop, but I got stuck with localStorage, useEffect, and React context. Basically, I have a product catalog with a button for every item there that should add a product to the cart.
It also creates an object in localStorage with that item's id and amount, which you select when adding the product to the cart.
My context file:
import * as React from 'react';
const CartContext = React.createContext();
export const CartProvider = ({ children }) => {
const [cartProducts, setCartProducts] = React.useState([]);
const handleAddtoCart = React.useCallback((product) => {
setCartProducts([...cartProducts, product]);
localStorage.setItem('cartProductsObj', JSON.stringify([...cartProducts, product]));
}, [cartProducts]);
const cartContextValue = React.useMemo(() => ({
cartProducts,
addToCart: handleAddtoCart, // addToCart is added to the button which adds the product to the cart
}), [cartProducts, handleAddtoCart]);
return (
<CartContext.Provider value={cartContextValue}>{children}</CartContext.Provider>
);
};
export default CartContext;
When multiple products are added, then they're correctly displayed in localStorage. I tried to log the cartProducts in the console after adding multiple, but then only the most recent one is logged, even though there are multiple in localStorage.
My component where I'm facing the issue:
const CartProduct = () => {
const { cartProducts: cartProductsData } = React.useContext(CartContext);
const [cartProducts, setCartProducts] = React.useState([]);
React.useEffect(() => {
(async () => {
const productsObj = localStorage.getItem('cartProductsObj');
const retrievedProducts = JSON.parse(productsObj);
if (productsObj) {
Object.values(retrievedProducts).forEach(async (x) => {
const fetchedProduct = await ProductService.fetchProductById(x.id);
setCartProducts([...cartProducts, fetchedProduct]);
});
}
}
)();
}, []);
console.log('cartProducts', cartProducts);
return (
<>
<pre>
{JSON.stringify(cartProductsData, null, 4)}
</pre>
</>
);
};
export default CartProduct;
My service file with fetchProductById function:
const domain = 'http://localhost:8000';
const databaseCollection = 'api/products';
const relationsParams = 'joinBy=categoryId&joinBy=typeId';
const fetchProductById = async (id) => {
const response = await fetch(`${domain}/${databaseCollection}/${id}?${relationsParams}`);
const product = await response.json();
return product;
};
const ProductService = {
fetchProductById,
};
export default ProductService;
As of now I just want to see all the products that I added to the cart in the console, but I can only see the most recent one. Can anyone see my mistake? Or maybe there's something that I missed?

This looks bad:
Object.values(retrievedProducts).forEach(async (x) => {
const fetchedProduct = await ProductService.fetchProductById(x.id);
setCartProducts([...cartProducts, fetchedProduct]);
});
You run a loop, but cartProducts has the same value in every iteration
Either do this:
Object.values(retrievedProducts).forEach(async (x) => {
const fetchedProduct = await ProductService.fetchProductById(x.id);
setCartProducts(cartProducts => [...cartProducts, fetchedProduct]);
});
Or this:
const values = Promise.all(Object.values(retrievedProducts).map(x => ProductService.fetchProductById(x.id)));
setCartProducts(values)
The last is better because it makes less state updates

Print the cartProducts inside useEffect to see if you see all the data
useEffect(() => {
console.log('cartProducts', cartProducts);
}, [cartProducts]);

if this line its returning corrects values
const productsObj = localStorage.getItem('cartProductsObj');
then the wrong will be in the if conditional: replace with
(async () => {
const productsObj = localStorage.getItem('cartProductsObj');
const retrievedProducts = JSON.parse(productsObj);
if (productsObj) {
Object.values(retrievedProducts).forEach(async (x) => {
const fetched = await ProductService.fetchProductById(x.id);
setCartProducts(cartProducts => [...fetched, fetchedProduct]);
});
}
}

Issue
When you call a state setter multiple times in a loop for example like in your case, React uses what's called Automatic Batching, and hence only the last call of a given state setter called multiple times apply.
Solution
In your useEffect in CartProduct component, call setCartProducts giving it a function updater, like so:
setCartProducts(prevCartProducts => [...prevCartProducts, fetchedProduct]);
The function updater gets always the recent state even though React has not re-rendered. React documentation says:
If the new state is computed using the previous state, you can pass a function to setState. The function will receive the previous value, and return an updated value.

Is there any hooks method in ReactJS like this.setState() in class components?

I want to set multiple states and call the useEffect function at once. Here's some code for better understanding.
const [activePage, setActivePage] = useState(1);
const [skip, setSkip] = useState(0);
const [limit, setLimit] = useState(10);
const getUserList = ()=>{
// do something
}
useEffect(() => {
getUserList();
}, [activePage, skip, limit]);
Here you can see I have three dependencies. setting all dependencies calls the getUserList() three times. all three dependencies are independent.
I want to call the getUserList() only once when I need to change all three states, similar to this.setState() in class components like:
this.setState({
activePage: //new value,
skip: // new value,
limit: // new value
},()=>getUserList())
Can someone please let me know if there is any method to achieve this?

This might not be the best solution but I think it should work. I imagine that when the state is changing three times at once, it's a special case, so you could create another state that would store a boolean that would be set to true in the case that it does happen. Then, the useEffect could be set for that boolean instead of all three states.
Special case where all 3 states are being updated:
setActivePage()
setSkip()
setLimit()
setAllChanged(true)
...
useEffect(() => {
getUserList();
}, [allChanged])

For your example, maybe immer.js will solve it better as your intended.
import produce from 'immer'
function FooComponent() {
const [state, setState] = useState({
activePage: 1,
skip: 0,
limit: 10
})
const getUserList = () => {}
// use immer to assign `payload` to `state`
const changeState = (payload) => {
setState(produce(draft => {
Objest.keys(payload).forEach(key => {
draft.key = payload.key
})
}))
}
changeState({
activePage: 2
})
useEffect(() => {
getUserList();
}, [state.activePage, state.skip, state.limit]);
return (< />)
}

is it possible to change the useState value without rendering? React

I need to change the useState without rendering the page.
First is it possible?
const UsersComponent = ({valueProp}) => {
const [users, setUsers] = useState(valueProp);
const [oldUsers, setoldUsers] = useState(value);
const allUsers = useSelector((state) =>
state.users
);
useEffect(() => {
dispatch(getUsersData());
}, [dispatch]);
useEffect(() => {
// assign users to state oldUsers
}, [dispatch]);
const onClickMergeTwoArrayOfUsers = () => {
let oldUsers = collectData(oldUsers);
const filteredUsers = intersectionBy(oldUsers, valueProp, "id");
setUsers(filteredUsers); // most important
console.log("filteredUsers", filteredUsers); // not changed
};
I tried everything nothing helps me.
useEffect(() => {
let oldUsers = collectData(oldUsers);
const filteredUsers = intersectionBy(oldUsers, valueProp, "id");
setUsers(filteredUsers); // most important
}, [users]); // RETURN INFINITIVE LOOP
I am also try ->
useEffect(() => {
let oldUsers = collectData(oldUsers);
const filteredUsers = intersectionBy(oldUsers, valueProp, "id");
setUsers(filteredUsers); // most important
}, []);
Load only one and that doesn't mean anything to me..
I am try with useRef ,but that doesn't help me in this case.
I will try to explain the basis of the problem.
I need to get one get data. After that get on the click of a button, I need to merge oldUsers and users without rendering, change the state. That is problem.
If there is no solution to this problem, tell me what I could do to solve the problem?
I am googling but without succes ... I am also try this solution from interent ->
const [state, setState] = useState({});
setState(prevState => {
// Object.assign would also work
return {...prevState, ...updatedValues};
});
no work.
I am also try with ->
const [state, setState] = useState(() => {
const initialState = someExpensiveComputation(props);
return initialState;
});
Here is problem because I need to asynchronous get only after that can I looping.

Using a ref is probably a better option for whatever it is you're ultimately trying to do.
Yes, it is possible, but it violates one of the core rules of React state: Do Not Modify State Directly.
React compares state values using Object.is equality, so if you simply mutate an object in state instead of replacing it with a new value that is not object-equal, then the state "update" will not cause a re-render (but this is considered a bug in your program!). Anyway, this is how you'd do it:
<div id="root"></div><script src="https://unpkg.com/react#17.0.2/umd/react.development.js"></script><script src="https://unpkg.com/react-dom#17.0.2/umd/react-dom.development.js"></script><script src="https://unpkg.com/#babel/standalone#7.17.1/babel.min.js"></script>
<script type="text/babel" data-type="module" data-presets="env,react">
const {useCallback, useState} = React;
function Example () {
const [state, setState] = useState([1]);
const logState = useCallback(() => console.log(state.join(', ')), [state]);
// Don't actually do this!!!
const mutateState = () => {
setState(arr => {
arr.push(arr.at(-1) + 1);
return arr;
});
};
return (
<>
<div>{state.join(', ')}</div>
<button onClick={mutateState}>Mutate state</button>
<button onClick={logState}>Log state</button>
</>
);
}
ReactDOM.render(<Example />, document.getElementById('root'));
</script>

How to make dispatch call synchronous in useeffect?

i am trying to paginate the data from my rest server using CoreUI Table Component.
i have problem getting the updated data from redux store after dispatch request in useEffect, i am using redux thunk, i know that dispatch is async, but is there a way to wait for the dispatch to be completed? i tired making the dispatch a Promise but it did not work.
I successfully get the updated result from action and reducer but in ProductsTable its the previous one, i checked redux devtools extension and i can see the state being changed.
i never get the latest value from store.
Also the dispatch is being called so many times i can see in the console window, it nots an infinite loop, it stops after sometime.
const ProductsTable = (props) => {
const store = useSelector((state) => state.store);
const dispatch = useDispatch();
const [items, setItems] = useState([]);
const [loading, setLoading] = useState(true);
const [page, setPage] = useState(1);
const [pages, setPages] = useState(1);
const [itemsPerPage, setItemsPerPage] = useState(5);
const [fetchTrigger, setFetchTrigger] = useState(0);
useEffect(() => {
setLoading(true);
const payload = {
params: {
page,
},
};
if (page !== 0)
dispatch(getAllProducts(payload));
console.log("runs:" + page)
console.log(store.objects)
if(!(Object.keys(store.objects).length === 0)){
setItems(store.objects.results)
setPages(store.objects.total.totalPages)
setLoading(false)
} else{
console.log("error")
setFetchTrigger(fetchTrigger + 1);
}
}, [page, fetchTrigger]);
return (
<CCard className="p-5">
<CDataTable
items={items}
fields={["title", "slug", {
key: 'show_details',
label: '',
_style: { width: '1%' },
sorter: false,
filter: false
}]}
loading={loading}
hover
cleaner
sorter
itemsPerPage={itemsPerPage}
onPaginationChange={setItemsPerPage}
<CPagination
pages={pages}
activePage={page}
onActivePageChange={setPage}
className={pages < 2 ? "d-none" : ""}
/>
</CCard>
)
}
export default ProductsTable

The reason the ProductsTable always has the previous state data is because the effect you use to update the ProductsTable is missing the store as dependency or more specifically store.objects.results; when the page and the fetchTrigger change the effect becomes stale because it isn't aware that when those dependencies change the effect should change.
useEffect(() => {
// store.objects is a dependency that is not tracked
if (!(Object.keys(store.objects).length === 0)) {
// store.objects.results is a dependency that is not tracked
setItems(store.objects.results);
// store.objects.total.totalPages is a dependency that is not tracked
setPages(store.objects.total.totalPages);
setLoading(false);
}
// add these dependencies to the effect so that everything works as expected
// avoid stale closures
}, [page, fetchTrigger, store.objects, store.objects.results, store.objects.total.totalPages]);
The dispatch is being called many times because you have a recursive case where fetchTrigger is a dependency of the effect but you also update it from within the effect. By removing that dependency you'll see much less calls to this effect, namely only when the page changes. I don't know what you need that value for because I dont see it used in the code you've shared, but if you do need it I recommend using the callback version of setState so that you can reference the value of fetchTrigger that you need without needing to add it as a dependency.
useEffect(() => {
// code
if (!(Object.keys(store.objects).length === 0)) {
// code stuffs
} else {
// use the callback version of setState to get the previous/current value of fetchTrigger
// so you can remove the dependency on the fetchTrigger
setFetchTrigger(fetchTrigger => fetchTrigger + 1);
}
// remove fetchTrigger as a dependency
}, [page, store.objects, store.objects.results, store.objects.totalPages]);
With those issues explained, you'd be better off not adding new state for your items, pages, or loading and instead deriving that from your redux store, because it looks like thats all it is.
const items = useSelector((state) => state.store.objects?.results);
const pages = useSelector((state) => state.store.objects?.total?.totalPages);
const loading = useSelector((state) => !Object.keys(state.store.objects).length === 0);
and removing the effect entirely in favor of a function to add to the onActivePageChange event.
const onActivePageChange = page => {
setPage(page);
setFetchTrigger(fetchTrigger => fetchTrigger + 1);
dispatch(getAllProducts({
params: {
page,
},
}));
};
return (
<CPagination
// other fields
onActivePageChange={onActivePageChange}
/>
);
But for initial results you will still need some way to fetch, you can do this with an effect that only runs once when the component is mounted. This should do that because dispatch should not be changing.
// on mount lets get the initial results
useEffect(() => {
dispatch(
getAllProducts({
params: {
page: 1,
},
})
);
},[dispatch]);
Together that would look like this with the recommended changes:
const ProductsTable = props => {
const items = useSelector(state => state.store.objects?.results);
const pages = useSelector(state => state.store.objects?.total?.totalPages);
const loading = useSelector(state => !Object.keys(state.store.objects).length === 0);
const dispatch = useDispatch();
const [page, setPage] = useState(1);
const [itemsPerPage, setItemsPerPage] = useState(5);
const [fetchTrigger, setFetchTrigger] = useState(0);
// on mount lets get the initial results
useEffect(() => {
dispatch(
getAllProducts({
params: {
page: 1,
},
})
);
},[dispatch]);
const onActivePageChange = page => {
setPage(page);
setFetchTrigger(fetchTrigger => fetchTrigger + 1);
dispatch(
getAllProducts({
params: {
page,
},
})
);
};
return (
<CCard className="p-5">
<CDataTable
items={items}
fields={[
'title',
'slug',
{
key: 'show_details',
label: '',
_style: { width: '1%' },
sorter: false,
filter: false,
},
]}
loading={loading}
hover
cleaner
sorter
itemsPerPage={itemsPerPage}
onPaginationChange={setItemsPerPage}
/>
<CPagination
pages={pages}
activePage={page}
onActivePageChange={onActivePageChange}
className={pages < 2 ? 'd-none' : ''}
/>
</CCard>
);
};
export default ProductsTable;

first of all you don't need any synchronous to achieve the results you want, you have to switch up your code so it doesn't use the state of react since you are already using some kind of global store ( i assume redux ); what you need to do is grab all the items straight from the store don't do an extra logic on the component (read for the separation of concerns); Also I would suggest to do the pagination on the server side not just paginate data on the front end. (getAllProducts() method to switch on fetching just a page of results and not all the products); Your code have alot of dispatches because you are using page and fetchTrigger as dependencies of useEffect hook that means every time the page or fetchTrigger value changes the code inside useEffect will run again resulting in another dispatch;
Here is a slightly modified part of your code, you need to add some extra stuff on your action and a loading param in your global state
const ProductsTable = (props) => {
const dispatch = useDispatch();
// PUT THE LOADING IN THE GLOBAL STATE OR HANDLE IT VIA A CALLBACK OR ADD A GLOBAL MECHANISM TO HANLE LOADINGS INSIDE THE APP
const loading = useSelector(() => state.store.loading)
const items = useSelector((state) => state.store.objects?.results); // ADD DEFAULT EMPTY VALUES FOR objects smthg like : { objects: { results: [], total: { totalPages: 0 } }}
const pages = useSelector((state) => state.store.objects?.total?.totalPages);
const [page, setPage] = useState(1);
const [itemsPerPage, setItemsPerPage] = useState(5);
const [fetchTrigger, setFetchTrigger] = useState(0); // I DONT UNDERSTAND THIS ONE
const fetchData = () => dispatch(getAllProducts({ params: { page }}));
useEffect(() => {
fetchData();
}, []);
return (
<CCard className="p-5">
<CDataTable
items={items}
fields={["title", "slug", {
key: 'show_details',
label: '',
_style: { width: '1%' },
sorter: false,
filter: false
}]}
loading={loading}
hover
cleaner
sorter
itemsPerPage={itemsPerPage}
onPaginationChange={setItemsPerPage}
<CPagination
pages={pages}
activePage={page}
onActivePageChange={setPage}
className={pages < 2 ? "d-none" : ""}
/>
</CCard>
)
}
export default ProductsTable

React Hook useEffect has a missing dependency when passing empty array as second argument

I have the following useEffect hook in my functional component that I only want to use once (when the component mounts) in order to load some data from an API:
const Gear = () => {
const [weaponOptions, setWeaponOptions] = useState([
{
key: "0",
label: "",
value: "null"
}
]);
const [weapon, setWeapon] = useState("null");
useEffect(() => {
console.log("Gear.tsx useEffect");
const fetchWeaponsOptions = async (): Promise<void> => {
const weaponsData = await getWeapons();
const newWeaponOptions: DropdownOptionType[] = [
...weaponOptions,
...weaponsData.map(({ id, name }) => {
return {
key: id,
label: name,
value: id
};
})
];
setWeaponOptions(newWeaponOptions);
};
fetchWeaponsOptions();
}, []);
// TODO add weapon dropdown on change, selected weapon state
const handleWeaponChange = ({ value }: DropdownOptionType): void => {
setWeapon(value);
};
return (
<div>
<h2>Gear:</h2>
<Dropdown
defaultValue={weapon}
label="Weapon"
name="weapon"
options={weaponOptions}
onChange={handleWeaponChange}
/>
</div>
);
};
A React documentation note states that this is valid practice when you only want the effect to run on mount an unmount:
If you want to run an effect and clean it up only once (on mount and
unmount), you can pass an empty array ([]) as a second argument. This
tells React that your effect doesn’t depend on any values from props
or state, so it never needs to re-run. This isn’t handled as a special
case — it follows directly from how the dependencies array always
works.
But I am getting the following create-react-app linter warning:
35:6 warning React Hook useEffect has a missing dependency: 'weaponOptions'. Either include it or remove the dependency array react-hooks/exhaustive-deps
The useEffect triggers if the weaponOptions array changes if I pass it as a dependency, resulting in an endless loop because the hook itself changes the weaponOptions state. The same thing happens if I omit the empty array argument.
What is the correct approach here?

I only want to use once (when the component mounts) in order to load some data from an API
Therefore according to your logic, you don't need to depend on the component's state:
const INITIAL = [
{
key: '0',
label: '',
value: 'null'
}
];
const App = () => {
const [weaponOptions, setWeaponOptions] = useState(INITIAL);
useEffect(() => {
const fetchWeaponsOptions = async () => {
const weaponsData = await getWeapons();
const weaponsOptions = [
...INITIAL, // No state dependency needed
...weaponsData.map(({ id, name }) => {
return {
key: id,
label: name,
value: id
};
})
];
setWeaponOptions(weaponsOptions);
};
}, []);
return <></>;
};
But, it is common when you want to use a useEffect once, and it depends on a state, to use a boolean reference like so:
const App = () => {
const [weaponOptions, setWeaponOptions] = useState(INITIAL);
const isFirstFetch = useRef(true);
useEffect(() => {
const fetchWeaponsOptions = async () => {...}
if (isFirstFetch.current) {
fetchWeaponsOptions();
isFirstFetch.current = false;
}
}, [weaponOptions]);
return <></>;
};

As you can see that is not an error but a warning. React is telling you that you are using weaponOptions inside useEffect but you didn't pass it as a dependency. Again, that is just a warning, you don't have to do it.