Value is undefined while passing data with Context API - javascript

I'm trying to pass data with Context API to child components. Value is getting undefined upon fetching it from a component.
Component Hierarchy:
passing data to a component MockTable and UsecasePane
MainContent -> MockTable
MainContent -> AddMock -> TabContent -> UsecasePane
=> MockContext.js
import React, { useState, useEffect, createContext } from "react";
import axios from "axios";
export const MockContext = createContext();
// provider
export const MockProvider = (props) => {
const [data, setData] = useState([]);
// data fetch and setting the state
return (
<MockContext.Provider data={[data, setData]}>
{props.children}
</MockContext.Provider>
);
};
Note: I'm getting response from the API.
Now in MainContent, components are encapsulated as follows:
// MainContent.js
import React from "react";
import { MockProvider } from "../MockContext";
const MainContent = () => {
return (
<MockProvider>
<div>
<CustomerTable />
<AddMock />
<MockTable />
</div>
</MockProvider>
);
};
When I try to fetch the data in MockTable or in UseCasePane, value is undefined.
// MockTable.js
import React, { useState, useEffect, useContext } from "react";
import { MockContext } from "./MockContext";
const MockTable = () => {
const [data, setData] = useContext(MockContext);
console.log(data);
// rest of the code
}
Please correct me where I'm going wrong :)
I tried to pass a String as well from the context and fetched in a component like:
return (
<MockContext.Provider data={"Hello"}>
{props.children}
</MockContext.Provider>
);
// in MockTable.js
const value = useContext(MockContext); ==> undefined

The correct prop to pass into the Provider is value, not data. (See: Context.Provider)
import React, { useState, useEffect, createContext } from "react";
import axios from "axios";
export const MockContext = createContext();
// provider
export const MockProvider = (props) => {
const [data, setData] = useState([]);
const fetchData = async () => {
const response = await axios
.get(config.App_URL.getAllRoute, {
params: {
customHostName: config.host,
type: config.type,
},
})
.catch((error) => {
console.error(`Error in fetching the data ${error}`);
});
console.log(response.data);
setData(response.data);
};
useEffect(() => {
fetchData();
}, []);
return (
<MockContext.Provider value={[data, setData]}>
{props.children}
</MockContext.Provider>
);
};

Related

Passing object as prop returns undefined in destination component ReactJS

I'm trying to pass a JSON object (id) returned from an API call to another component via props and use that object(id) to fetch more data from a different endpoint. The problem is, when i pass the prop using object literal to the api, it gives an error undefined but when i console log the object(id) it works fine. What could be the issue? Just started learning React.
component passing object as prop
import axios from "axios";
import React, { useEffect, useState } from "react";
import { useParams } from "react-router-dom";
import Cast from "./Cast";
const DetailsView = () => {
const { id } = useParams();
const [details, setDetails] = useState([]);
useEffect(() => {
axios
.get(
`https://api.themoviedb.org/3/movie/${id}?api_key=<<api_key>>&language=en-US`
)
.then((response) => {
setDetails(response.data);
});
}, []);
return (
<div className="w-full h-[650px] text-white">
<<bunch of code>>
<Cast id={details?.id}/>
</div>
);
};
export default DetailsView;
component receiving prop
import React, { useState, useEffect } from "react";
import axios from "axios";
const Cast = (props) => {
const [cast, setCast] = useState([]);
const sid = props.id;
useEffect(() => {
axios
.get(
`https://api.themoviedb.org/3/movie/${sid}/credits?api_key=<<api_key>>&language=en-US`
)
.then((response) => {
setCast(response.data.cast);
console.log(response.data.cast);
});
}, []);
console.log(sid);
return (
<div className="absolute">
{cast && cast.map((item, index) => <p className="">{item.name}</p>)}
<p>{sid}</p>
</div>
);
};
export default Cast;
It doesn't work initially but when I edit the code, since the change is happening live, it fetches the data but when I refresh the page, Axios reports an error 404
xhr.js:220 GET https://api.themoviedb.org/3/movie/**undefined**/credits?api_key=56fbaac7fd77013cc072d285a17ec005&language=en-US 404
Your id property does not exist until the API call is completed, and there is a rerender after setDetails.
You can check if id exists and based on that render your Card component. Also, looks like details is an object not an array, so I changed the useState statement to reflect that.
import axios from "axios";
import React, { useEffect, useState } from "react";
import { useParams } from "react-router-dom";
import Cast from "./Cast";
const DetailsView = () => {
const { id } = useParams();
const [details, setDetails] = useState({});
useEffect(() => {
axios
.get(
`https://api.themoviedb.org/3/movie/${id}?api_key=<<api_key>>&language=en-US`
)
.then((response) => {
setDetails(response.data);
});
}, []);
return (
<div className="w-full h-[650px] text-white">
<<bunch of code>>
{details?.id && <Cast id={details?.id}/>}
</div>
);
};
export default DetailsView;

undefined useState React after setting it to an object

Goal: Fetch data from api then assign it to a state for further processing.
Issue: After setting the data to my useState it is still undefined.
Questions:
How would one solve this problem?
Am I misunderstanding the useState hook?
import "./styles.css";
import axios from "axios";
import { useEffect, useState } from "react";
export default function App() {
const [userData, setUserData] = useState();
const functionz = () => {
return axios
.get("https://randomuser.me/api/")
.then(({ data }) => data.results);
};
useEffect(async () => {
const data = await functionz();
setUserData(data);
}, []);
if (userData) {
console.log(userData);
}
return (
<div className="App">
<h1>Hello CodeSandbox</h1>
<h2>Edit to see some magic happen!</h2>
</div>
);
}
You have to make sure your function is returning the axios call. Then await whatever comes out of it in your useEffect. Then proceed to adding it to your state. See example.
import React, { useState, useEffect } from 'react'
import axios from "axios";
const Api = () => {
const [usersData, setUsersData] = useState(null)
const fetchRandomUserData = () => axios.get('the-url')
useEffect(() => {
fetchRandomUserData()
.then(resp => {
setUsersData(resp.data.results)
})
.catch(e => {
console.log('Error: ', e)
})
}, [])
console.log(usersData)
return <div></div>
}
export default Api

How to test react functional component async call

I have a functional component. Inside the component, I have called SpecialistsListService service. The service called the API via Axios. I have to test the async function getSpecialistsList and useEffect functions but I don't do that anyone helps me to solve the problem. When I used class component I simply call the method like await wrapper.instance.getSpecialistsList() then check the state but the functional component approach are different I think.
import React, { useState, useEffect } from "react";
import SpecialistsListService from "../../../services/specialists";
import SpecialistsPageView from "./SpecialistsPageView";
import "./index.scss";
export default function SpecialistsPage() {
const [specialistsList, setSpecialistsList] = useState([]);
const [isLoading, setIsLoading] = useState(true);
const specialistsListService = new SpecialistsListService();
useEffect(() => {
getSpecialistsList();
}, []);
async function getSpecialistsList() {
const specialistsListData = await specialistsListService.getSpecialistsList();
setSpecialistsList(specialistsListData);
setIsLoading(false);
}
return (
<SpecialistsPageView isLoading={isLoading} specialists={specialistsList} />
);
}
Splitting your component into custom hooks and component make your life easier to test and more readable by splitting UI and logic.
The custom hooks will look like this
useSpecialistsList.js
import { useState, useEffect } from "react";
const useSpecialistsList = (specialistsListService) => {
const [specialistsList, setSpecialistsList] = useState([]);
const [isLoading, setIsLoading] = useState(true);
useEffect(() => {
getSpecialistsList();
}, []);
async function getSpecialistsList() {
const specialistsListData = await specialistsListService.getSpecialistsList();
setSpecialistsList(specialistsListData);
setIsLoading(false);
}
return {
isLoading: isLoading,
specialistsList: specialistsList
}
}
export default useSpecialistsList;
The component look like this
import React from "react";
import SpecialistsListService from "../../../services/specialists";
import SpecialistsPageView from "./SpecialistsPageView";
import useSpecialistsList from "./useSpecialistsList";
import "./index.scss";
export default function SpecialistsPage() {
const {isLoading, specialistsList} = useSpecialistsList(new SpecialistsListService());
return (
<SpecialistsPageView isLoading={isLoading} specialists={specialistsList} />
);
}
Now you can test your hooks using "#testing-library/react-hooks"
Test will look like this
import {renderHook} from "#testing-library/react-hooks";
import useSpecialistsList from "./useSpecialistsList";
import SpecialistsListService from "../../../services/specialists";
describe("useSpecialistsList", ()=>{
it('Should return userDetails loading as false', async ()=> {
const {result, waitForNextUpdate} = renderHook(()=> useSpecialistsList(new SpecialistsListService()));
expect(result.current.isLoading).toEqual(true);
await waitForNextUpdate();
expect(result.current.isLoading).toEqual(false);
});
})
Here waitForNextUpdate call the useEffect (Generally update the component)
To read more about testing custom hooks use this like

REST API Response Flickering on Page Load

I've got component that displays contact information from a dealer as chosen by the user. To be more specific, a user selects their location, setting a cookie which then is used to define the API call. I pull in the contact information of the dealer in that location using Axios, store it in a context, and then display the information as necessary through several components: the header, a "current location" component etc. However, I'm having an issue with the content flickering each time the page is refreshed.
I've tried storing the JSON response in local storage, but, for a brief moment on page load, it shows as undefined, making the flicker continue. Obviously, I'm needing to eliminate that so that the data persists.
I've got it working via ApiContext, and I'm displaying the data in my Header component. Below is the code for both:
ApiContext.tsx
import React, { createContext, useEffect, useState } from 'react';
import axios from 'axios';
const contextObject = {} as any;
export const context = createContext(contextObject);
export const ApiContext = ({ children }: any) => {
const [selectedDealer, setselectedDealer] = useState(`1`);
useEffect(() => {
axios
.get(`${process.env.GATSBY_API_ENDPOINT}/${selectedDealer}`)
.then((response) => setselectedDealer(response.data));
}, [selectedDealer]);
const changeDealer = (id: any) => {
setselectedDealer(id);
};
const { Provider } = context;
return (
<Provider value={{ data: selectedDealer, changeDealer: changeDealer }}>
{children}
</Provider>
);
};
Header.tsx
import React, { ReactNode, useContext, useEffect, useState } from 'react';
import Logo from 'assets/svg/logo.svg';
import css from 'classnames';
import { Button } from 'components/button/Button';
import { Link } from 'components/link/Link';
import { MenuIcon } from 'components/menu-icon/MenuIcon';
import { context } from 'contexts/ApiContext';
import { NotificationBar } from '../notification-bar/NotificationBar';
import s from './Header.scss';
import { MainNav } from './navigation/MainNav';
interface HeaderProps {
navigationContent: ReactNode;
}
export const Header = ({ navigationContent }: HeaderProps) => {
const [scrolled, setScrolled] = useState(false);
const [open, setOpen] = useState(false);
const data = useContext(context);
const buttonLabel = data ? data.name : 'Find a Dealer';
const buttonLink = data ? `tel:${data.phone}` : '/find-a-dealer';
useEffect(() => {
const handleScroll = () => {
const isScrolled = window.scrollY > 10;
if (isScrolled !== scrolled) {
setScrolled(!scrolled);
}
};
document.addEventListener('scroll', handleScroll, { passive: true });
return () => {
document.removeEventListener('scroll', handleScroll);
};
}, [scrolled]);
return (
<>
<NotificationBar notificationContent={navigationContent} />
<header className={scrolled ? css(s.header, s.header__scrolled) : s.header}>
<nav className={s.header__navigation}>
<ul className={s.header__container}>
<li className={s.header__logo}>
<Link to="/" className={s.header__link}>
<Logo />
</Link>
</li>
<li className={s.header__primary}>
<MainNav navigationItems={navigationContent} />
</li>
<li className={s.header__utility}>
<Button href={buttonLink}>{buttonLabel}</Button>
</li>
<li className={s.header__icon}>
<MenuIcon onClick={() => setOpen(!open)} />
</li>
</ul>
</nav>
</header>
</>
);
};
I would assume that this is because the API call is being triggered each time the page is refreshed, so I wonder if there's any way to persist the data in a more efficient way?
Thanks in advance!
Your ApiContext.tsxcould persist the data in localStorage is such a way:
import React, { createContext } from 'react';
import axios from 'axios';
import { makeUseAxios } from 'axios-hooks';
import { useCookie } from 'hooks/use-cookie';
const contextObject = {} as any;
export const context = createContext(contextObject);
const useAxios = makeUseAxios({
axios: axios.create({ baseURL: process.env.GATSBY_API_ENDPOINT }),
});
const loadData = (cookie) => {
const stored = localStorage.getItem("data");
const parsed = JSON.parse(stored);
// You can also store a lastSync timestamp along with the data, so that you can refresh them if necessary
if (parsed) return parsed;
const [{data}] = useAxios(`${cookie}`);
if (!isEqual(parsed, data)) {
localStorage.setItem('data', JSON.stringify(data));
}
return data
}
export const ApiContext = ({ children }: any) => {
const [cookie] = useCookie('one-day-location', '1');
const [{ data }] = loadData(cookie);
const { Provider } = context;
return <Provider value={data}>{children}</Provider>;
};
The above implementation will only fetch the data once, so remember to refresh them at some point inside your code and update the localStorage item, or use a timestamp to compare and force the api call as commented in my code.
Keep in mind that even this implementation may take a fraction of a second to be completed, so I would suggest to always use loaders/spinners/skeletons while your application is fetching the required data.
I got this worked out, using a hook that persists my state, storing it in a localStorage item.
usePersistState.ts
import { useEffect, useState } from 'react';
export const usePersistState = (key: string, defaultValue: string) => {
const [value, setValue] = useState(() => {
if (typeof window !== 'undefined') {
const stickyValue = window.localStorage.getItem(key);
return stickyValue !== null ? JSON.parse(stickyValue) : defaultValue;
}
});
useEffect(() => {
window.localStorage.setItem(key, JSON.stringify(value));
}, [key, value]);
return [value, setValue];
};
Then, in ApiContext, I set my default state, but when that state changes, it updates and persists the state. Here's my context component now:
ApiContext.tsx
import React, { createContext, useEffect } from 'react';
import { usePersistState } from 'hooks/use-persist-state';
import axios from 'axios';
const contextObject = {} as any;
export const context = createContext(contextObject);
const LOCAL_STORAGE_KEY_SELECTED_DEALER = 'selectedDealerInformation';
export const ApiContext = ({ children }: any) => {
const [selectedDealer, setselectedDealer] = usePersistState(LOCAL_STORAGE_KEY_SELECTED_DEALER, '1');
useEffect(() => {
axios
.get(`${process.env.GATSBY_API_ENDPOINT}/${selectedDealer}`)
.then((response) => setselectedDealer(response.data));
}, [selectedDealer]);
const changeDealer = (id: any) => {
setselectedDealer(id);
};
localStorage.setItem(LOCAL_STORAGE_KEY_SELECTED_DEALER, JSON.stringify(selectedDealer));
const { Provider } = context;
return (
<Provider value={{ data: selectedDealer, changeDealer: changeDealer }}>{children}</Provider>
);
};

ReactJS: How to correctly pass variables with fetch results through context?

Need help, just started to learn React. I'm trying to pass variables with json data to a component for further use, but catching the errors. what should I change to use variables with json() data from Store.js in the product.js component? THanks for your time!
https://jsfiddle.net/constant101/xu7zdn26/3/ for better visibility
//Store export(receiving data from the server and assigning them to variables)
import React, {useState, useEffect} from 'react'
import axios from 'axios'
export const ListContext = React.createContext([]);
export const ItemContext = React.createContext([]);
function Store() {
const [storeProducts, setStoreProducts] = useState([]);
const [detailProduct, setDetailProduct] = useState([]);
useEffect(() => {
axios.get('/products/')
.then(res => {
console.log(res)
setStoreProducts(res.data)
})
},[])
console.log('storeProducts:', storeProducts)
useEffect(() => {
axios.get('/products/:productId')
.then(res => {
console.log(res)
setDetailProduct(res.data)
})
},[])
console.log('detail product:', detailProduct)
return (
<ListContext.Provider value={[storeProducts, setStoreProducts]}>
<ItemContext.Provider value={[detailProduct, setDetailProduct]}>
<product/>
</ItemContext.Provider>
</ListContext.Provider>
);
}
export const detailProduct
//product.js ( file that uses data from the fetch)
import React, { useReducer, createContext, useContext, useState } from 'react';
import {ListContext, ItemContext } from '../Store';
import { useProductActions } from '../actions';
import { SET_PRODUCT_DETAILS } from '../actions/types';
const [storeProducts] = useContext(ListContext);
const [detailProduct] = useContext(ItemContext);
let tempProducts = [];
storeProducts.forEach(item => tempProducts.push({ ...item })
);
const initialState = {
products: tempProducts,
productDetails: { ...detailProduct }
};
console.log(storeProducts)
const productReducer = (state, action) => {
switch (action.type) {
case SET_PRODUCT_DETAILS:
return {
...state,
productDetails: action.payload
};
default:
throw new Error('Invalid action type');
}
};
export const ProductContext = createContext(initialState);
export const useProductState = () => {
return useContext(ProductContext);
};
export const ProductProvider = ({ children }) => {
const [state, dispatch] = useReducer(productReducer, initialState);
const productActions = useProductActions(state, dispatch);
return (
<ProductContext.Provider value={{ productState: state, productActions }}>
{children}
</ProductContext.Provider>
);
};
Well, assuming your request is right, i saw a syntax mistake. You should pass
<ListContext.Provider value={{storeProducts, setStoreProducts}}> instead of
<ListContext.Provider value={[storeProducts, setStoreProducts]}>
The reason:
a provider requires a prop called value with an Object inside.
In that case, you were passing an array.
it would be the same if you did:
<ListContext.Provider
value={{
storeProducts: storeProducts,
setStoreProducts: setStoreProducts
}}
>
but to follow the DRY principle, it's recommended to do that way described earlier

Categories

Resources