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.

why wont jsx render firestore data

I'm trying to GET data from firestore and render it, in the most basic way possible. I can console.log the data, but as soon as I try to render it via JSX, it doesn't. Why is this?
import React from 'react'
import { useState, useEffect } from 'react'
import {db} from '../../public/init-firebase'
export default function Todo() {
const [todo, setTodo] = useState()
const myArray = []
//retrive data from firestore and push to empty array
function getData(){
db.collection('Todos')
.onSnapshot((querySnapshot) => {
querySnapshot.forEach((doc) => {
console.log(doc.id +'pushed to myArray')
myArray.push(doc.id)
})
})
}
useEffect(() => {
getData()
}, [])
return (
<>
<div>
<h1>Data from firestore: </h1>
{myArray.map((doc) => {
<h1>{doc.id}</h1>
console.log('hi')
})}
</div>
</>
)
}

First, change myArray to State like this:
const [myArray, setMyArray] = useState([]);
Every change in myArray will re-render the component.
Then, to push items in the State do this:
function getData(){
db.collection('Todos')
.onSnapshot((querySnapshot) => {
querySnapshot.forEach((doc) => {
console.log(doc.id +'pushed to myArray')
setMyArray(oldArray => [...oldArray, doc.id])
})
})
}
You're just pushing the ID in myArray, so when to show try like this:
{myArray.map((id) => {
console.log('hi')
return <h1 key={id}>{id}</h1>
})}

If you look closely,
{myArray.map((doc) => {
<h1>{doc.id}</h1>
console.log('hi')
})}
those are curly braces {}, not parenthesis (). This means that although doc exists, nothing is happening since you are just declaring <h1>{doc.id}</h1>. In order for it to render, you have to return something in the map function. Try this instead:
{myArray.map((doc) => {
console.log('hi')
return <h1>{doc.id}</h1>
})}

In order to force a "re-render" you will have to use the hooks that you defined
https://reactjs.org/docs/hooks-intro.html
function getData(){
db.collection('Todos')
.onSnapshot((querySnapshot) => {
querySnapshot.forEach((doc) => {
console.log(doc.id +'pushed to myArray')
myArray.push(doc.id)
})
})
// in case the request doesn't fail, and the array filled up with correct value using correct keys:
// i'd setState here, which will cause a re-render
setTodo(myArray)
}

Multiple rendering problem and how can I use the useEffect here

Filtering data by using this function, if I am calling this function in useEffect than its pushes to search results and not working well.
const AdvanceSearch = (props) => {
const [region, setRegion] = useState("");
const [searchStuhl, setSearchStuhl] = useState("");
const filterData = (async ()=> {
const filtereddata = await props.data.filter((item) => {
return (
item.region.toLowerCase().includes(region.toLowerCase())
&& item.stuhl.toLowerCase().includes(searchStuhl.toLowerCase())
)}
) await props.history.push({
pathname: '/searchResults/',
state:
{
data:filtereddata
}
})
})
//If the props. history.push is pass here instead of the above function then its sending the empty array and not the filtered data
const handleSubmit = async (e) => {
e.preventDefault()
await filterData();
}

when you are changing the navigation URL with some data and there is multiple rendering then the following problem would be there.
Check your route configuration for the path. is it configured to hold the changed path: in this scenario, you get fluctuated UI or we can say multiple renders
yes you can use useEffect hooks to change the path and set the data here is the peace of code. here whenever your props.data will be changed filteredData will run and it will return the value when data will be available.
const filteredData = useCallback(() => {
if(props.data){
const filteredData = props.data.filter((item) => (
item.region.toLowerCase().includes(region.toLowerCase())
&&item.stuhl.toLowerCase().includes(searchStuhl.toLowerCase())
));
return filteredData
}
},
[props && props.data]);
useEffect(()=> {
const data = filteredData();
if(data){
props.history.push({
pathname:'/search-results',
state:{data}
});
}
},[filteredData])

Try to remove async / await from the function. You don't need them to filter an array.

How to run useQuery inside forEach?

I have loop - forEach - which find productId for every element of array. I want to fetch my database by productId using apollo query.
How to do it?
products.forEach(({ productId, quantity }) =>
// fetch by 'productId'
);

From the rules of hooks:
Don’t call Hooks inside loops, conditions, or nested functions. Instead, always use Hooks at the top level of your React function. By following this rule, you ensure that Hooks are called in the same order each time a component renders.
Hooks cannot be used inside a loop, so you can't use them inside a forEach callback.
You should create a separate component for each product that only uses the useQuery hook once. You can then map over the products and return the component for each one:
const YourComponent = () => {
...
return products.map(({ productId, quantity }) => (
<Product key={productId} productId={productId} quantity={quantity} />
))
}
const Product = () => {
const { data, error, loading } = useQuery(...)
// render your data accordingly
}

To run useQuery based on logic or manually multiple times by setting refetchOnWindowFocus & enable properties to false and then calling method refetch(). example as below.
const RefetchExample = () => {
const manualFetch = {
refetchOnWindowFocus: false,
enabled: false
}
const GetAssetImage = async () => {
const {data} = await axiosInstance.get("Your API")
return data
}
const {assetImage, refetch} = useQuery('assetImage', GetAssetImage, manualFetch)
const imageFetch = () => {
refetch();
}
return (
<Button onClick={imageFetch}>Refetch</Button>
)
}
export default RefetchExample

If you want to perform multiple calls to useQuery then you can't do that in a forEach, map etc. You need to use useQueries e.g.
function Products({ productIds }) {
const productQueries = useQueries({
queries: productIds.map(productId => {
return {
queryKey: ['productById', productId],
queryFn: () => fetchProductById(productId),
}
})
})
Example taken from: https://tanstack.com/query/v4/docs/guides/parallel-queries

Firebase with useeffect cleanup function

I'm trying to get all data with the 'public' parameter of a firebase collection and then use useffect, but the console accuses error.
I took this structure from firebase's documentation:
https://firebase.google.com/docs/firestore/query-data/get-data#get_multiple_documents_from_a_collection
but the console says 'Warning: Can't perform a React state update on an unmounted component. This is a no-op, but it indicates a memory leak in your application. To fix, cancel all subscriptions and asynchronous tasks in a useEffect cleanup function'
So I went to this other page:
https://firebase.google.com/docs/firestore/query-data/listen#detach_a_listener
But I'm not using onSnapshot, besides firebase documentation seems wrong to me, since unsub is not a function.
useEffect(() => {
let list = []
const db = firebase.firestore().collection('events')
let info = db.where('public', '==', 'public').get().then(snapshot => {
if (snapshot.empty) {
console.log('No matching documents.');
setLoading(false)
return;
}
snapshot.forEach(doc => {
console.log(doc.id, "=>", doc.data())
list.push({
id: doc.id,
...doc.data()
})
})
setEvents(list)
setLoading(false)
})
.catch(error => {
setLoading(false)
console.log('error => ', error)
})
return () => info
}, [])

You need to invoke the listener function to detach and unmount.
https://firebase.google.com/docs/firestore/query-data/listen#detach_a_listener
useEffect(() => {
let list = []
const db = firebase.firestore().collection('events')
let info = ...
return () => info() # invoke to detach listener and unmount with hook
}, [])

You don't need to clear a .get(), it's like a normal Fetch api call.
You need to make sure your component is still mounted when you setLoading
Example:
// import useRef
import { useRef } from 'react'
// At start of your component
const MyComponent = () =>{
const isMounted = useRef(false)
useEffect(() => {
isMounted.current = true;
return () => isMounted.current = false;
}, [])
// Your query
db.where('public', '==', 'public').get().then(snapshot => {
if(isMounted.current){
// set your state here.
}
})
return <div></div>
}