Develop Reference

React - how can I make the return of JSX wait until my useEffect() ended [duplicate]

I have fetch method in useEffect hook:
export const CardDetails = () => {
const [ card, getCardDetails ] = useState();
const { id } = useParams();
useEffect(() => {
fetch(`http://localhost:3001/cards/${id}`)
.then((res) => res.json())
.then((data) => getCardDetails(data))
}, [id])
return (
<DetailsRow data={card} />
)
}
But then inside DetailsRow component this data is not defined, which means that I render this component before data is fetched. How to solve it properly?

Just don't render it when the data is undefined:
export const CardDetails = () => {
const [card, setCard] = useState();
const { id } = useParams();
useEffect(() => {
fetch(`http://localhost:3001/cards/${id}`)
.then((res) => res.json())
.then((data) => setCard(data));
}, [id]);
if (card === undefined) {
return <>Still loading...</>;
}
return <DetailsRow data={card} />;
};

There are 3 ways to not render component if there aren't any data yet.
{data && <Component data={data} />}
Check if(!data) { return null } before render. This method will prevent All component render until there aren't any data.
Use some <Loading /> component and ternar operator inside JSX. In this case you will be able to render all another parts of component which are not needed data -> {data ? <Component data={data} /> : <Loading>}

If you want to display some default data for user instead of a loading spinner while waiting for server data. Here is a code of a react hook which can fetch data before redering.
import { useEffect, useState } from "react"
var receivedData: any = null
type Listener = (state: boolean, data: any) => void
export type Fetcher = () => Promise<any>
type TopFetch = [
loadingStatus: boolean,
data: any,
]
type AddListener = (cb: Listener) => number
type RemoveListener = (id: number) => void
interface ReturnFromTopFetch {
addListener: AddListener,
removeListener: RemoveListener
}
type StartTopFetch = (fetcher: Fetcher) => ReturnFromTopFetch
export const startTopFetch = function (fetcher: Fetcher) {
let receivedData: any = null
let listener: Listener[] = []
function addListener(cb: Listener): number {
if (receivedData) {
cb(false, receivedData)
return 0
}
else {
listener.push(cb)
console.log("listenre:", listener)
return listener.length - 1
}
}
function removeListener(id: number) {
console.log("before remove listener: ", id)
if (id && id >= 0 && id < listener.length) {
listener.splice(id, 1)
}
}
let res = fetcher()
if (typeof res.then === "undefined") {
receivedData = res
}
else {
fetcher().then(
(data: any) => {
receivedData = data
},
).finally(() => {
listener.forEach((cb) => cb(false, receivedData))
})
}
return { addListener, removeListener }
} as StartTopFetch
export const useTopFetch = (listener: ReturnFromTopFetch): TopFetch => {
const [loadingStatus, setLoadingStatus] = useState(true)
useEffect(() => {
const id = listener.addListener((v: boolean, data: any) => {
setLoadingStatus(v)
receivedData = data
})
console.log("add listener")
return () => listener.removeListener(id)
}, [listener])
return [loadingStatus, receivedData]
}
This is what myself needed and couldn't find some simple library so I took some time to code one. it works great and here is a demo:
import { startTopFetch, useTopFetch } from "./topFetch";
// a fakeFetch
const fakeFetch = async () => {
const p = new Promise<object>((resolve, reject) => {
setTimeout(() => {
resolve({ value: "Data from the server" })
}, 1000)
})
return p
}
//Usage: call startTopFetch before your component function and pass a callback function, callback function type: ()=>Promise<any>
const myTopFetch = startTopFetch(fakeFetch)
export const Demo = () => {
const defaultData = { value: "Default Data" }
//In your component , call useTopFetch and pass the return value from startTopFetch.
const [isloading, dataFromServer] = useTopFetch(myTopFetch)
return <>
{isloading ? (
<div>{defaultData.value}</div>
) : (
<div>{dataFromServer.value}</div>
)}
</>
}

Try this:
export const CardDetails = () => {
const [card, setCard] = useState();
const { id } = useParams();
useEffect(() => {
if (!data) {
fetch(`http://localhost:3001/cards/${id}`)
.then((res) => res.json())
.then((data) => setCard(data))
}
}, [id, data]);
return (
<div>
{data && <DetailsRow data={card} />}
{!data && <p>loading...</p>}
</div>
);
};

using React useEffect to fetch data and controll component

i am trying to query data using useEffect add those data to state and render them but nothing comes up unless a state in the app changes. this is what i have done so far Please help, Thanks in Advance.
useEffect
// fetchCampaigns
(async () => {
dispatch(showTopLoader());
try {
const res = await getAgentCampaigns(authToken, "accepted");
setCampaigns(res.data.campaigns);
let leads: any[] = [];
const fetchCampaignLeads = async (id: string) => {
try {
const res = await getCampaignLeads(authToken, id);
return res.data.campaignLeads;
} catch (error) {}
};
// loop through campaigns and get leads
let resS: any[] = [];
campaigns.forEach((campaign: any, i: number) => {
const id = campaign?.Campaign?.id;
fetchCampaignLeads(id)
.then((leadsRes) => {
leads.push(leadsRes[i]);
if (id === leadsRes[i]?.campaignId)
return resS.push({
...campaign,
leads: leadsRes,
});
return (resS = campaigns);
})
.catch(() => {})
.finally(() => {
console.log(resS);
setCampaigns(resS);
});
});
} catch (error) {
} finally {
dispatch(hideTopLoader());
}
})();
}, []);
whole component
import { useDispatch, useSelector } from "react-redux";
import _ from "lodash";
import styles from "../../../styles/CreateLeads.module.css";
import {
getAgentCampaigns,
getCampaignLeads,
} from "../../../utils/requests/campaign";
import {
hideTopLoader,
showTopLoader,
} from "../../../store/actions/TopLoader/topLoaderActions";
import CampaignSection from "./CampaignSection";
import Empty from "../Empty/Empty";
import SectionHeader from "../SectionHeader/SectionHeader";
import SearchBar from "../SearchBar/SearchBar";
import { RootState } from "../../../store/store";
const CreateLeadsCardsWrapper: React.FC = () => {
const authToken = useSelector(
(store: any) => store.authenticationReducer.authToken
);
const [stateCampaigns, setStateCampaigns] = React.useState<any[]>([]);
const [showCampaigns, setShowCampaigns] = React.useState<boolean>(false);
const [campaigns, setCampaigns] = React.useState<any[]>(stateCampaigns);
const [filter, setFilter] = React.useState<string>("");
const dispatch = useDispatch();
const handleChange = (e: React.ChangeEvent<HTMLInputElement>) => {
// Reset filter
setFilter("");
let campaignSearch = e.target.value.trim();
if (campaignSearch.length === 0) {
return;
}
let campaignSearchLower = campaignSearch.toLowerCase();
let campaignSearchUpper = campaignSearch.toUpperCase();
let campaignSearchSentence =
campaignSearch.charAt(0).toUpperCase() + campaignSearch.slice(1);
let results = stateCampaigns.filter(
({ leads }: { leads: any[] }, i) =>
leads &&
leads?.some(
(lead: any) =>
lead.firstName.includes(campaignSearch) ||
lead.firstName.includes(campaignSearchLower) ||
lead.firstName.includes(campaignSearchUpper) ||
lead.firstName.includes(campaignSearchSentence) ||
lead.lastName.includes(campaignSearch) ||
lead.lastName.includes(campaignSearchLower) ||
lead.lastName.includes(campaignSearchUpper) ||
lead.lastName.includes(campaignSearchSentence) ||
lead.email.includes(campaignSearch) ||
lead.email.includes(campaignSearchLower) ||
lead.email.includes(campaignSearchUpper) ||
lead.email.includes(campaignSearchSentence) ||
lead.phoneNo.includes(campaignSearch) ||
lead.phoneNo.includes(campaignSearchLower) ||
lead.phoneNo.includes(campaignSearchUpper) ||
lead.phoneNo.includes(campaignSearchSentence)
)
);
setCampaigns(results);
};
React.useEffect(() => {
// fetchCampaigns
(async () => {
dispatch(showTopLoader());
try {
const res = await getAgentCampaigns(authToken, "accepted");
setCampaigns(res.data.campaigns);
let leads: any[] = [];
const fetchCampaignLeads = async (id: string) => {
try {
const res = await getCampaignLeads(authToken, id);
return res.data.campaignLeads;
} catch (error) {}
};
// loop through campaigns and get leads
let resS: any[] = [];
campaigns.forEach((campaign: any, i: number) => {
const id = campaign?.Campaign?.id;
fetchCampaignLeads(id)
.then((leadsRes) => {
leads.push(leadsRes[i]);
if (id === leadsRes[i]?.campaignId)
return resS.push({
...campaign,
leads: leadsRes,
});
return (resS = campaigns);
})
.catch(() => {})
.finally(() => {
console.log(resS);
setCampaigns(resS);
});
});
} catch (error) {
} finally {
dispatch(hideTopLoader());
}
})();
}, []);
React.useEffect(() => {
setCampaigns(stateCampaigns);
campaigns.length > 0 && setShowCampaigns(true);
console.log(showCampaigns);
dispatch(hideTopLoader());
}, []);
return (
<div className={styles.wrappers}>
{/* Multi step form select a campaign first then fill info on the next step */}
<SectionHeader text="Campaign Leads" />
{showCampaigns && stateCampaigns.length === 0 && (
<>
<Empty description="No agents yet" />
<p>Join a campaign.</p>
</>
)}
{showCampaigns && stateCampaigns.length > 0 && (
<>
<p className="text-grey-500">Create Leads for Campaigns.</p>
<section className={styles.container}>
<SearchBar
placeholder="Find Campaign Leads"
onChange={handleChange}
/>
{campaigns.map((item: any) => (
<CampaignSection
key={item?.Campaign?.id}
id={item?.Campaign?.id}
name={item?.Campaign?.name}
imageUrl={item?.Campaign?.iconUrl}
campaignType={item?.Campaign?.type}
productType={item?.Campaign?.Products[0]?.type}
/>
))}
</section>
</>
)}
</div>
);
};
export default CreateLeadsCardsWrapper;

there are two things wrong in yoour code :
1- you should not have two useeffects with the same dependencies in your case: [] you have to merge those useeffects into one or change the second one's dependencies
2- doing async code in useeffect can be problematic sometimes. it is better to create an async function which does the query to the backend and sets the state and the call the function in your useeffect like below :
const getData = async()=>{
// do some queries and set the state
}
React.useeffect(()=>{
getData()
},[])

Search function now working in React photo gallary

Working on a small application that takes a pexels api and displays photos dynamically. When I send the search request for my api to fectch based on the new params, it does actually update the page with new photos but not the ones based on the params. I though I got the search function correct, maybe it's cause I'm not using it in a useEffect? But if I did use it in a useEffect, I wouldn't be able to set it on the onClick handle. I tried to console.log the query I was getting from the onChange but it doesn't seem like it's getting the result. What am I doing wrong?
import { useState, useEffect } from 'react'
import pexelsApi from './components/pexelsApi'
import './App.css'
const App = () => {
const [images, setImages] = useState([]);
const [loading, setLoading] = useState(false);
const [nextPage, setNextPage] = useState(1);
const [perPage, setPerPage] = useState(25);
const [query, setQuery] = useState('');
const [error, setError] = useState('');
useEffect(() => {
const getImages = async () => {
setLoading(true);
await pexelsApi.get(`/v1/curated?page=${nextPage}&per_page=${perPage}`)
.then(res => {
setImages([...images, ...res.data.photos]);
setLoading(false);
}).catch(er => {
if (er.response) {
const error = er.response.status === 404 ? 'Page not found' : 'Something wrong has happened';
setError(error);
setLoading(false);
console.log(error);
}
});
}
getImages();
}, [nextPage, perPage]);
const handleLoadMoreClick = () => setNextPage(nextPage + 1)
const search = async (query) => {
setLoading(true);
await pexelsApi.get(`/v1/search?query=${query}&per_page=${perPage}`)
.then(res => {
setImages([...res.data.photos]);
console.log(res.data)
setLoading(false);
console.log(query)
})
}
if (!images) {
return <div>Loading</div>
}
return (
<>
<div>
<input type='text' onChange={(event) => setQuery(event.target.value)} />
<button onClick={search}>Search</button>
</div>
<div className='image-grid'>
{images.map((image) => <img key={image.id} src={image.src.original} alt={image.alt} />)}
</div>
<div className='load'>
{nextPage && <button onClick={handleLoadMoreClick}>Load More Photos</button>}
</div>
</>
)
};
export default App
import axios from 'axios';
export default axios.create({
baseURL: `https://api.pexels.com`,
headers: {
Authorization: process.env.REACT_APP_API_KEY
}
});

Your main issue is that you've set query as an argument to your search function but never pass anything. You can just remove the arg to have it use the query state instead but you'll then need to handle pagination...
// Helper functions
const getCuratedImages = () =>
pexelsApi.get("/v1/curated", {
params: {
page: nextPage,
per_page: perPage
}
}).then(r => r.data.photos)
const getSearchImages = (page = nextPage) =>
pexelsApi.get("/v1/search", {
params: {
query,
page,
per_page: perPage
}
}).then(r => r.data.photos)
// initial render effect
useEffect(() => {
setLoading(true)
getCuratedImages().then(photos => {
setImages(photos)
setLoading(false)
})
}, [])
// search onClick handler
const search = async () => {
setNextPage(1)
setLoading(true)
setImages(await getSearchImages(1)) // directly load page 1
setLoading(false)
}
// handle pagination parameter changes
useEffect(() => {
// only action for subsequent pages
if (nextPage > 1) {
setLoading(true)
const promise = query
? getSearchImages()
: getCuratedImages()
promise.then(photos => {
setImages([...images, ...photos])
setLoading(false)
})
}
}, [ nextPage ])
The reason I'm passing in page = 1 in the search function is because the setNextPage(1) won't have completed for that first page load.

Mapping through a fetched array from firebase but nothing shows up even though the array is not empty [duplicate]

This question already has answers here:
How do I return the response from an asynchronous call?
(41 answers)
Closed 1 year ago.
I fetched an array of products from firebase with the normal way :
export const getUsersProducts = async uid => {
const UsersProducts = []
await db.collection('products').where("userID", "==", uid).get().then(snapshot => {
snapshot.forEach(doc => UsersProducts.push(doc.data()))
})
return UsersProducts
}
and the fetched array shows up in the dom normally, but when I tried to fetch it with onSnapshot method it didnt show up on the DOM even though in appeared in my redux store and when I console log it, it shows up normally.
export const getUsersProducts = uid => {
let UsersProducts = []
db.collection('products').where("userID", "==", uid).onSnapshot(querySnapshot => {
querySnapshot.docChanges().forEach(change => {
if (change.type === "added") {
UsersProducts.push(change.doc.data())
}
})
})
return UsersProducts
}
here is the code used to show it in the DOM
const MyProducts = () => {
const CurrentUserInfos = useSelector(state => state.userReducer.currentUserInfos)
const searchQuery = useSelector(state => state.productsReducer.searchQuery)
const myProducts = useSelector(state => state.productsReducer.usersProducts)
const dispatch = useDispatch()
const settingUsersProductList = async () => {
try {
const usersProducts = getUsersProducts(CurrentUserInfos.userID)
dispatch(setUsersProducts(usersProducts))
console.log(myProducts)
} catch (err) {
console.log(err)
}
}
useEffect(() => {
settingUsersProductList()
}, [CurrentUserInfos])
return (
<div className="my-products">
<div className="my-products__search-bar">
<SearchBar />
</div>
<div className="my-products__list">
{
Object.keys(myProducts).length===0 ? (<Loading />) : (myProducts.filter(product => {
if(searchQuery==="")
return product
else if(product.title && product.title.toLowerCase().includes(searchQuery.toLowerCase()))
return product
}).map(product => {
return(
<ProductItem
key={product.id}
product={product}
/>
)
}))
}
</div>
</div>
)
}
export default MyProducts

You are returning the array before promise is resolved hence its empty. Try this:
export const getUsersProducts = async uid => {
const snapshot = await db.collection('products').where("userID", "==", uid).get()
const UsersProducts = snapshot.docs.map(doc => doc.data())
return UsersProducts
}
For onSnapshot, add the return statement inside of onSnapshot,
export const getUsersProducts = uid => {
let UsersProducts = []
return db.collection('products').where("userID", "==", uid).onSnapshot(querySnapshot => {
querySnapshot.docChanges().forEach(change => {
if (change.type === "added") {
UsersProducts.push(change.doc.data())
}
})
return UsersProducts
})
}

React Native: Saving array via AsyncStorage and retrieving it

I am trying to get an array of objects from my Redux-Store state called user and save it to async storage and use useState with the response to set the state before I retrieve it and view it with the FlatList however I am getting an error along the lines of Warning: Can't perform a React state update on an unmounted component. The user details is being set to the redux store in another component and then being retrieved from the current component I am displaying. Please could I get your help . I would really appreciate it. Thank you in advance!!!
const TheUser = (props) => {
//user is an array from redux store
const user = useSelector(state => state.account.cookbook)
const [getUser, setGetUser] = useState()
const saveUserAsync = async () => {
await AsyncStorage.setItem('user', JSON.stringify(user))
}
saveUserAsync()
AsyncStorage.getItem('user').then(response => {
setGetUser(response)
})
return (
<FlatList
data={getUser}
keyExtractor={item => item.id}
renderItem={itemData =>
<MyUser
name={itemData.item.name}
image={itemData.item.imageUri}
details={itemData.item.details.val}
/>
}
/>
)
}
export default TheUser

You can use useEffect hook to solve this problem.
IS_MOUNTED variable will track if component is mounted or not.
let IS_MOUNTED = false; // global value
const TheUser = (props) => {
//user is an array from redux store
const user = useSelector(state => state.account.cookbook)
const [getUser, setGetUser] = useState()
const saveUserAsync = async () => {
await AsyncStorage.setItem('user', JSON.stringify(user))
}
AsyncStorage.getItem('user').then(response => {
if(IS_MOUNTED)
{
setGetUser(JSON.parse(response));
}
});
useEffect(() => {
IS_MOUNTED = true;
saveUserAsync();
return (() => {
IS_MOUNTED = false;
})
},[])
return (
<FlatList
data={getUser}
keyExtractor={item => item.id}
renderItem={itemData =>
<MyUser
name={itemData.item.name}
image={itemData.item.imageUri}
details={itemData.item.details.val}
/>
}
/>
)
}
export default TheUser

import { useEffect } from "react"
let isMount = true
const TheUser = (props) => {
//user is an array from redux store
const user = useSelector(state => state.account.cookbook)
// const [getUser, setGetUser] = useState()
// useEffect(() => {
// const saveUserAsync = async () => {
// await AsyncStorage.setItem('user', JSON.stringify(user))
// const response = await AsyncStorage.getItem('user')
// if (isMount)
// setGetUser(JSON.parse(response))
// }
// saveUserAsync()
// }, [user])
// useEffect(() => {
// isMount = true
// return () => {
// isMount = false
// }
// }, [])
return (
<FlatList
// data={getUser}
data={user}
keyExtractor={item => item.id}
renderItem={itemData =>
<MyUser
name={itemData.item.name}
image={itemData.item.imageUri}
details={itemData.item.details.val}
/>
}
/>
)
}
export default TheUser