how can I use UseContext to make this const '' data '' accessible throughout my project? I'm trying to implement but I can't. It doesn't have to be with UseContext, it was just a way that I researched
import api from '../../services/api';
import React, {useContext} from 'react';
export default async function getItems() {
try {
const data = await api.get("/list-results");
return data;
} catch (error) {
return error
}
}
First, create yourself a context:
const MyContext = React.createContext(defaultValue);
Then call your getItems() and store the result in a state and pass it to your context provider:
const [storedData, setStoredData] = useState<MyData | null>(null);
useEffect(() => {
getItems().then((data) => setStoredData(data));
}, []);
if (!storedData) return <div>Loading</div>;
return <MyContext.Provider value={}><MyApp/> </MyContext.Provider>;
Ideally do some more error handling in there.
And finally, get your context using useContext in a component somewhere in MyApp:
const data = useContext(MyContext);
Code is untested and should be seen as pseudo-code.
Related
I have a straightforward react component that looks so in AllWords.js :
import React, { useEffect, useState } from 'react';
import consts from '../../constants/Constants.js';
function AllWords() {
const [words, setWords] = useState([]);
async function fetchData(){
const response= await fetch(consts.FETCH_URL);
const data = await (response.json());
setWords(data);
};
// API: useEffect( () => { . . . return cleanup; },[var_n_whose_change_triggers_useEffect . . .] );
useEffect(() => {fetchData()}, [] );
return (
<>
{
words.map(w=> <div>{w.word}</div>)
}
</>
);
}
export default AllWords;
I would like to refactor the fetchData() method out of the component into another file (basically a separate .js file that holds the fetch call).
What I would like is to have created a file titled FetchAllWords.js under src/actions/ & then import it. & use that.
I have several questions :
do I need to set the state in the FetchAllWords.js and then useSelector to extract the state in AllWords.js?
in FetchAllWords.js do I need to usedispatch to dispatch a method call setting the state? I would like to just setState in FetchAllWords.js and then extract it in AllWords.js. This is what I have so far:
import consts from '../constants/Constants.js';
import { useState } from 'react';
async function FetchAllWords(){
const [words, setWords] = useState([]);
const response= await fetch(consts.FETCH_URL);
const data = await (response.json());
setWords(data);
}
export default FetchAllWords;
I am unsure how to import this and use it in AllWords.js. I am using the following statement :
import wordList from '../../actions/FetchAllWords';
Then I am trying to use wordList as a handle to the file '../../actions/FetchAllWords.js' & attempting to access the async function FetchAllWords so wordList.FetchAllWords();
Firstly , the editor (VSCode) won't let me see the function despite the import call.
Secondly I am getting an error (something like) :
TypeError: _actions_FetchAllWords_js__WEBPACK_IMPORTED_MODULE_3__.default.FetchAllWords is not a function
Any insight or help would be appreciated since rather uneasy with JS & React.
The github repo is : https://github.com/mrarthurwhite/hooks-p5-react-redux
EDIT: As per David's suggestions :
So AllWords.js React component is :
import React, { useEffect, useState } from 'react';
import wordList from '../../services/Fetch.js';
function AllWords() {
const [words, setWords] = useState([]);
function fetchData(){
wordList.fetchAllWords().then(
data => setWords(data)
);
};
// API: useEffect( () => { . . . return cleanup; },[var_n_whose_change_triggers_useEffect . . .] );
useEffect(() => {fetchData()}, [] );
return (
<>
{
words.map(w=> <div>{w.word}</div>)
}
</>
);
}
export default AllWords;
And Fetch.js is :
import consts from '../constants/Constants.js';
class Fetch {
async fetchAllWords(){
const response= await fetch(consts.FETCH_URL);
const data = await (response.json());
return data;
}
}
export default Fetch;
No, don't worry about state in the external file. Just focus on the one thing it should do, perform the AJAX operation. At its simplest it's just a function, something like:
import consts from '../../constants/Constants.js';
const fetchAllWords = async () => {
const response = await fetch(consts.FETCH_URL);
const data = await (response.json());
return data;
}
export default fetchAllWords;
You can even make it a class which contains this function, if you plan on adding other service operations as well. (Fetch specific word? Find word? etc.) The point is that this does just one thing, provide data. Let the React components handle React state.
Within the component you'd just use that to get your data. Something like:
import React, { useEffect, useState } from 'react';
import fetchAllWords from '../../services/FetchAllWords.js';
function AllWords() {
const [words, setWords] = useState([]);
useEffect(() => {
fetchAllWords().then(w => setWords(w));
}, []);
return (
<>
{
words.map(w=> <div>{w.word}</div>)
}
</>
);
}
export default AllWords;
Overall it's a matter of separating concerns. The service performs the AJAX operation and returns the meaningful data, internally concerned with things like JSON deserialization and whatnot. The React component maintains the state and renders the output, internally concerned with updating state after useEffect runs and whatnot.
I created a file which would contain helper functions for querying the database. My problem is that I have to get my access token through the Context API but I can't call the useContext hook outside of a functional component. I could place the functions inside one, but I don't need the component, it would be unused. What is the best practice here?
import React, { useContext } from "react";
import axios from "axios";
import { AuthContext } from "../../contexts/auth-context.js";
import { mongoQuery } from "../xhr/QueryMongo";
const { getAccessToken } = useContext(AuthContext);
export async function fetchUserData(userId) {
const sRealmApp = "...";
const CancelTokenLogin = axios.CancelToken;
const sourceLogin = CancelTokenLogin.source();
let token = await getAccessToken("users");
const userQuery = `query {user (query:{_id:"${userId}"}) {name, role, residence }}`;
let queryResult = await mongoQuery(token, sRealmApp, userQuery, sourceLogin);
if (queryResult.data.data !== null && queryResult.data.data.user !== null) {
return queryResult.data.data.user;
} else return false;
//other similar helper functions....
}
(Why I'm creating a new file: I'm refactoring my code because I have a file which has 400 lines of code, but it's not a big project. So I decided to extract code which connects to the database because it's not directly linked to the component.)
You can always provide the context as a parameter for your helper function.
helperFunction.js
fetchUserData(userId, token) {
... rest of code
}
Component.js
Then get the token from your component using useContext
import React, {useContext, useEffect} from 'react';
import context from 'location of context';
import fetchUserData from 'location of helper function';
const Component = () => {
const userId = 123; // Not sure where you are getting this, but for example.
const {getToken} = useContext(context);
useEffect(() => {
fetchUserData(userId, getToken());
}, []);
return (JSX)
};
Although, I don't think this is the best approach. I've done this before and it makes testing a nightmare. Creating a customHook would be a better approach imo.
I am new to React Context.
I need to call the API in react context to use its data throughout my react application. Also the same API needs to be called on some CRUD operation on various component of react application.
For now I am storing API data in redux which I don't want to store.
Here is what I have tried..
context.js File
import React, { useState, createContext,useEffect } from 'react';
import {getData} from './actionMethods';
const NewContext = createContext();
function newContextProvider(props) {
useEffect(async () => {
const {dataValue} = await getData()
console.log("Data " , dataValue)
}, [])
return (
<NewContext.Provider
value={{
state: {
},
actions: {
}
}}
>
{props.children}
</NewContext.Provider>
);
}
const newContextConsumer = newContext.Consumer;
export { newContextProvider, newContextConsumer, newGridContext };
actionMethods.js
export function getData() {
let config = getInstance('GET', `${prefix}/xyz/list`)
return axios(config).then(res => res.data).catch(err => {
console.log(err)
})
}
when any CRUD operation performs , I need to call the API from the context.js file to get the data from API and store in the context.
Any help would be great.
Thank You.
First we create the Context and pass it an initial value.
In order to fetch data and keep track of the returned value, we create a state inside the component. This component will manage the fetched data and pass it in the Context Provider.
To call an async function inside useEffect we need to wrap it and call it inside useEffect callback.
export const NewContext = createContext({
my_data: {} // Initial value
});
export const NewContextProvider = props => {
const [my_data, setMyData] = useState({});
useEffect(() => {
const fetchMyData = async () => {
const { dataValue } = await getData();
if (dataValue) {
setMyData(dataValue);
} else {
// There was an error fetching the data
}
};
fetchMyData();
}, []);
return (
<NewContext.Provider
value={{
my_data
}}
>
{props.children}
</NewContext.Provider>
);
};
To use this Context in a component we use the useContext hook. Remember that this component needs to be wrapped by the Provider we just created.
import React, { useContext } from "react";
import { NewContext } from "./NewContext"; // The file where the Context was created
export const MyComponent = props => {
const { my_data } = useContext(NewContext);
return //...
};
Let me know if something is not clear.
Could someone please explain what is going wrong in simple terms so I know how to fix this and can deal with it next time I encounter it.
I have looked through all related questions I could find on stackoverflow and haven't been able to fix it, if I have missed one that answers this then please link it.
I have had this error in the past but usually that was just because I had a typo (e.g. a capital instead of a lowercase) or did not import something correctly however that is not the case this time as far as I can tell.
FIRST CODE app.js
SECOND CODE interactions.js
Here is my code
import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';
import Navbar from './Navbar'
import Web3 from 'web3';
import { connect } from 'react-redux'
// import Token from '../abis/Token.json'
import {
loadWeb3,
loadAccount,
loadToken,
loadExchange
} from '../store/interactions'
class App extends Component {
componentWillMount() {
this.loadBlockchainData(this.props.dispatch)
}
async loadBlockchainData(dispatch) {
const web3 = loadWeb3(dispatch)
const network = await web3.eth.net.getNetworkType()
const networkId = await web3.eth.net.getId()
const accounts = await loadAccount(web3, dispatch) // <<--
const token = loadToken(web3, networkId, dispatch)
loadExchange(web3, networkId, dispatch)
}
// ......................
function mapStateToProps(state) {
return {
account: accountSelector(state)
}
}
export default connect(mapStateToProps)(App);
import Web3 from 'web3'
import {
web3Loaded,
web3AccountLoaded,
tokenLoaded,
exchangeLoaded
} from './actions'
import Token from '../abis/Token.json'
import Exchange from '../abis/Exchange.json'
export const loadWeb3 = (dispatch) => {
const web3 = new Web3(Web3.givenProvider || 'http://localhost:7545')
dispatch(web3Loaded(web3))
return web3
}
export const loadAccount = async (web3, dispatch) => {
const accounts = await web3.eth.getAccounts()
const account = accounts[0]
dispatch(web3AccountLoaded(account))
return account
}
export const loadToken = async (web3, networkId, dispatch) => {
try {
const token = new web3.eth.Contract(Token.abi, Token.networks[networkId].address) // new 이거 의존성(버전) 문제 이거 조심!!!!!
dispatch(tokenLoaded(token))
return token
} catch (error) {
window.alert('Contract not deployed to the current network. Please select another network with Metamask.')
return null
}
}
export const loadExchange = async (web3, networkId, dispatch) => {
try {
const exchange = new web3.eth.Contract(Exchange.abi, Exchange.networks[networkId].address)
dispatch(exchangeLoaded(exchange))
return exchange
} catch (error) {
window.alert('Contract not deployed to the current network. Please select another network with Metamask.')
return null
}
}
i don'k now why this happening to me
but please let me know this problem if you know this issue
The problem seems to be that you do not define or import the accountSelector function anywhere.
You usually define Redux selector functions in your reducer definition files: they take the current Redux store state as argument (and optionally the connected component props) and return the value to be used in your MapStateToProps object property.
Ex.
export const accountSelector = (state) => state.account
You can read more about selectors on the dedicated Redux resources page
replace this
function mapStateToProps(state) {
return {
account: accountSelector(state)
}
}
with this
function mapStateToProps(state) {
return {
account: state.accountSelector
}
}
you are passing complete state in variable instead of accessing.
for your reference, how to access please go through official documentation for your better understanding Redux
Trying to get along with React new Hooks and ActionCable, but stuck with the problem that I can't get the right data in Rails when trying to send state.
I've tried to use send() method immediately after doing setState() and send my updated data, but for some reason, the data which received on the Rails part is old.
For example, if I put "Example" to the input I'll see "{"data"=>"Exampl"} on the Rails side. I suppose the data update the state later than my request goes.
If I send() value from e.target.value everything works fine
Therefore I've tried to use new useEffect() hook and send data there. But I get only data when rendering the page. Afterward, I don't get anything and sometimes get error RuntimeError - Unable to find subscription with an identifier. Seems like effect hook sends data too early or something.
I'm pretty new to Hooks and WebSockets. Would love to get any help here. I can share Rails code, but there is only a receiver and nothing else.
First exmaple:
import React, { useState, useEffect } from "react"
import ActionCable from 'actioncable'
function Component(props) {
const [data, setData] = useState("");
const cable = ActionCable.createConsumer('ws://localhost:3000/cable');
const sub = cable.subscriptions.create('DataChannel');
const handleChange = (e) => {
setData(e.target.value)
sub.send({ data });
}
return (
<input value={data} onChange={handleChange}/>
)
}
Tried to useEffect and move send() there:
useEffect(() => {
sub.send({ data });
}, [data]);
I'd love to find a way to correctly use React and ActionCable. And use hooks if it's possible.
I was trying an approach similar to Oleg's but I could not setChannel inside the action cable create subscription callback. I had to setChannel outside of the callback but within the useEffect hook. Below is the solution that worked for me.
create consumer in index.js and provide the consumer through Context to App.
index.js
import React, { createContext } from 'react'
import actionCable from 'actioncable'
... omitted other imports
const CableApp = {}
CableApp.cable = actionCable.createConsumer('ws://localhost:3000/cable')
export const ActionCableContext = createContext()
ReactDOM.render(
<Router>
... omitted other providers
<ActionCableContext.Provider value={CableApp.cable}>
<App />
</ActionCableContext.Provider>
</Router>,
document.getElementById('root')
)
Use the cable context in your child component and create subscription in useEffect hooks; unsubscribe in clean up
import React, { useState, useEffect, useContext } from 'react'
import { useParams } from 'react-router-dom'
... omitted code
const [channel, setChannel] = useState(null)
const { id } = useParams()
const cable = useContext(ActionCableContext)
useEffect(() => {
const channel = cable.subscriptions.create(
{
channel: 'MessagesChannel',
id: id,
},
{
received: (data) => {
receiveMessage(data)
},
}
)
setChannel(channel)
return () => {
channel.unsubscribe()
}
}, [id])
const sendMessage = (content) => {
channel.send(content)
}
You can register your cable at root component like that:
import actionCable from 'actioncable';
(function() {
window.CableApp || (window.CableApp = {});
CableApp.cable = actionCable.createConsumer('ws://localhost:3000/cable')
}).call(this);`
so it will be available as global variable;
and then in any component where you want to create channel and send data:
const [channel, setChannel] = useState(null);
useEffect(() => {
CableApp.cable.subscriptions.create(
{
channel: 'YourChannelName',
},
{
initialized() {
setChannel(this)
},
},
);
}, []);
return <button onClick={() => channel.send(some_data)} >Send counter</button>
Your problem is here:
const handleChange = (e) => {
setData(e.target.value)
sub.send({ data });
}
setData is like setState in that the state is only updated after the render i.e. after the function has exited. You are sending the current data not the new data. Try this:
const handleChange = (e) => {
const newData = e.target.value;
setData(newData)
sub.send({ data: newData });
}