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Array doesn't save information ReactJS

import './App.css';
import io from 'socket.io-client'
import { useEffect, useRef, useState } from 'react'
import React from 'react';
import ReactDOM from "react-dom/client";
const socket = io.connect("http://localhost:3001");
function App() {
const [message, setMessage] = useState("");
const [state, setState] = useState([]);
const [chat, setChat] = useState([]);
const socketRef = useRef();
const sendMessage = () => {
socket.emit("send_message", { message });
};
const renderChat = () => {
return (
chat.map(msg => {
console.log(msg.data)
return (
<h3>{msg.data["message"]}</h3>
)
})
)
}
useEffect(() => {
socketRef.current = io.connect("http://localhost:3001")
socketRef.current.on("receive_message", ({ message }) => {
setChat([ ...chat, { message } ])
})
return () => socketRef.current.disconnect()
},
[ chat ]
)
return (
<div className="App">
<input placeholder="Message..." onChange={(event) => {
setMessage(event.target.value);}}
/>
<button onClick={sendMessage}>Send Message</button>
<h1>Message:</h1>
{renderChat()}
</div>
);
}
export default App;
For some reason the useEffect that needs to store information doesn't work. I have tried a few solutions to store new values in an array useState but I always get this error:
When I do it like this:
useEffect(() => {
socket.on("receive_message", message => {
setChat([...chat, {message}]);
});
}, [socket])
it works but it doesn't save the information (it always has only 1 value which is the latest input text).

You can do it like in the second approach you mentioned, using the previous State:
useEffect(() => {
socket.on("receive_message", message => {
setChat(prevState => [...prevState, {message}]);
});
}, [socket])

You try
useEffect(() => {
socket.on("receive_message", ({ message }) => {
if(!!message){
setChat(prev => [ ...prev, { message } ])
}
})
return () => socket.disconnect()
},[ socket ])

TypeError: Cannot read property 'params' of undefined for updating categories

So basically I'm trying to create a code that allows me to update the slug with the use of params.
Don't know why My code throws this error.
"TypeError: Cannot read property 'params' of undefined in react".
I tried replacing
useEffect(() => {
loadCategory();
}, []);
with
useEffect(() => {
if(match.params.slug) loadOrders()
}, [match.params.slug])
but it still didn't work.
This is the code I wrote.
import React, { useState, useEffect } from "react";
import {
HistoryContainer,
HistoryBg,
TextContainer2,
TextContainer3,
Text,
CatForm,
FormLabel,
FormControl,
ButtonPrimary,
} from "./CategoryUpdateElements";
import AdminNav from "../AdminNav/index";
import { toast } from "react-toastify";
import { useSelector } from "react-redux";
import { getCategory, updateCategory } from "../../../functions/category";
const CategoryUpdate = ({ history, match }) => {
const { user } = useSelector((state) => ({ ...state }));
const [name, setName] = useState("");
const [loading, setLoading] = useState(false);
useEffect(() => {
loadCategory();
}, []);
const loadCategory = () =>
getCategory(match.params.slug).then((c) => setName(c.data.name));
const handleSubmit = (e) => {
e.preventDefault();
// console.log(name);
setLoading(true);
updateCategory(match.params.slug, { name }, user.token)
.then((res) => {
// console.log(res)
setLoading(false);
setName("");
toast.success(`"${res.data.name}" is updated`);
history.push("/admin/category");
})
.catch((err) => {
console.log(err);
setLoading(false);
if (err.response.status === 400) toast.error(err.response.data);
});
};
return (
<>
<HistoryContainer>
<HistoryBg>
<AdminNav />
<TextContainer2>
<TextContainer3>
{loading ? <Text>Loading..</Text> : <Text>Update category</Text>}
<CatForm onSubmit={handleSubmit}>
<FormLabel>Name</FormLabel>
<FormControl
type="text"
value={name}
onChange={(e) => setName(e.target.value)}
autoFocus
required
/>
<ButtonPrimary>Save</ButtonPrimary>
</CatForm>
</TextContainer3>
</TextContainer2>
</HistoryBg>
</HistoryContainer>
</>
);
};
export default CategoryUpdate;
UPDATE:
To add context to this problem. This code lets me update the name of the slug, but the TypeError doesn't let me follow through with this haha. I was actually following a tutorial regarding this and obviously, his code works. I was sure that I was following it properly as I wrote the code exactly like his but the only difference is my ui.
I also tried console logging match and after checking it out, what I saw was "undefined" which is not surprising.. It should have shown me the slug but instead it gave me "undefined".
This is his code which allows him to update his slug.
import React, { useState, useEffect } from "react";
import AdminNav from "../../../components/nav/AdminNav";
import { toast } from "react-toastify";
import { useSelector } from "react-redux";
import { getCategory, updateCategory } from "../../../functions/category";
const CategoryUpdate = ({ history, match }) => {
const { user } = useSelector((state) => ({ ...state }));
const [name, setName] = useState("");
const [loading, setLoading] = useState(false);
useEffect(() => {
loadCategory();
}, []);
const loadCategory = () =>
getCategory(match.params.slug).then((c) => setName(c.data.name));
const handleSubmit = (e) => {
e.preventDefault();
// console.log(name);
setLoading(true);
updateCategory(match.params.slug, { name }, user.token)
.then((res) => {
// console.log(res)
setLoading(false);
setName("");
toast.success(`"${res.data.name}" is updated`);
history.push("/admin/category");
})
.catch((err) => {
console.log(err);
setLoading(false);
if (err.response.status === 400) toast.error(err.response.data);
});
};
const categoryForm = () => (
<form onSubmit={handleSubmit}>
<div className="form-group">
<label>Name</label>
<input
type="text"
className="form-control"
onChange={(e) => setName(e.target.value)}
value={name}
autoFocus
required
/>
<br />
<button className="btn btn-outline-primary">Save</button>
</div>
</form>
);
return (
<div className="container-fluid">
<div className="row">
<div className="col-md-2">
<AdminNav />
</div>
<div className="col">
{loading ? (
<h4 className="text-danger">Loading..</h4>
) : (
<h4>Update category</h4>
)}
{categoryForm()}
<hr />
</div>
</div>
</div>
);
};
export default CategoryUpdate;
Still new to coding. Hope you guys can help me with this ^_^

I think your problem with match which is getting as the props. If you are having trouble with handle match props please try
useRouteMatch instaed.
import { useRouteMatch } from "react-router-dom";
function YourComponent() {
let match = useRouteMatch();
// Do whatever you want with the match...
return <div />;
}
I think this is more convinent to use.
For more examples

How to have changeable values in input React JS?

I was trying to set my value in the input value! but after that, I cannot write anything in the input field! I wanted to set values from the back end in value!
We are writing an admin channel to edit the article for that we need already existing article values to edit the article! What am I doing wrong! or Maybe you can suggest a better way to edit the article in the admin channel!
here is the code:
import React, { useState, useEffect } from 'react';
import axios from 'axios';
import { useParams } from 'react-router';
const EditArticle = (props) => {
const [editValues, setEditValues] = useState([]);
const [changedValues, setChangedValues] = useState('');
console.log('values', editValues);
console.log('changed', changedValues);
const params = useParams();
console.log(params);
const resultsId = params.id;
console.log('string', resultsId);
const [authTokens, setAuthTokens] = useState(
localStorage.getItem('token') || ''
);
const setTokens = (data) => {
localStorage.setItem('token', JSON.stringify(data));
setAuthTokens(data);
// setToken(data['dataValues']['token']);
};
useEffect(() => {
const fetchData = async () => {
try {
const res = await axios.get(
`${process.env.REACT_APP_API_URL}/article/${resultsId}`
);
setEditValues(res.data);
} catch (err) {}
};
fetchData();
}, [resultsId]);
const inputValue = editValues;
const userToken = props.token;
return (
<div>
<form value={{ authTokens, setAuthTokens: setTokens }}>
<input
value={editValues.title || ''}
onChange={(input) => setChangedValues(input.target.value)}
type='text'
/>
<input
// ref={editValues.shortDesc}
value={editValues.shortDesc}
onChange={(input) => setChangedValues(input.target.value)}
type='text'
/>
<button type='submit'>send</button>
</form>
</div>
);
};
export default EditArticle;

your onChange handler is updating a different state property than what is being used as the value on the input (editValues vs changedValues).
Also you can pass a defaultValue to input that will get used as the default value only.
See more here https://reactjs.org/docs/uncontrolled-components.html

you can use just do it just using editValues. try this:
I just reproduced it without the api call to run the code.
import React, { useState, useEffect } from "react";
const EditArticle = (props) => {
const [editValues, setEditValues] = useState([]);
console.log("values", editValues);
const [authTokens, setAuthTokens] = useState(
localStorage.getItem("token") || ""
);
const setTokens = (data) => {
localStorage.setItem("token", JSON.stringify(data));
setAuthTokens(data);
// setToken(data['dataValues']['token']);
};
useEffect(() => {
const fetchData = async () => {
try {
//here get the data from api and setstate
setEditValues({ title: "title", shortDesc: "shortDesc" });
} catch (err) {}
};
fetchData();
}, []);
return (
<div>
<form value={{ authTokens, setAuthTokens: setTokens }}>
<input
value={editValues.title || ""}
onChange={(input) => setEditValues({title: input.target.value})}
type="text"
/>
<input
value={editValues.shortDesc}
onChange={(input) => setEditValues({shortDesc: input.target.value})}
type="text"
/>
<button type="submit">send</button>
</form>
</div>
);
};
export default EditArticle;

Why are the elements from a mapping function not rendering?

Summarize the problem
I have a page within a Gatsby JS site that accepts state via a provider, and some of that activity is able to be used, however, I am unable to provide the contents from a mapping function that is given via context.
Expected result: the expected elements from the mapping function would render
Actual result: the elements in question are not rendered
No error messages
Describe what you've tried
I thought the issue was not explicitly entering in return on the arrow function in question, but that does not change any of the output
Also, rather than try to access the method directly on the page (via a context provider) I moved the method directly into the Provider hook. This did not change any of the rendering.
Show some code
here is Provider.js
import React, { useState, useEffect } from 'react';
import he from 'he';
export const myContext = React.createContext();
const Provider = props => {
const [state, setState] = useState({
loading: true,
error: false,
data: [],
});
const [page, setPage] = useState(1);
const [score, setScore] = useState(0);
const [correctAnswers, setCorrectAnswers] = useState([]);
const [allQuestions, setAllQuestions] = useState([]);
const [answers, setAnswers] = useState([]);
const [right, setRight] = useState([]);
const [wrong, setWrong] = useState([]);
function clearScore() {
updatedScore = 0;
}
function clearRights() {
while (rights.length > 0) {
rights.pop();
}
}
function clearWrongs() {
while (wrongs.length > 0) {
wrongs.pop();
}
}
let updatedScore = 0;
let rights = [];
let wrongs = [];
const calcScore = (x, y) => {
for (let i = 0; i < 10; i++) {
if (x[i] === y[i]) {
updatedScore = updatedScore + 1;
rights.push(i);
} else wrongs.push(i);
}
}
useEffect(() => {
fetch('https://opentdb.com/api.php?amount=10&difficulty=hard&type=boolean')
.then(response => {
return response.json()
})
.then(json => {
const correctAnswer = json.results.map(q => q['correct_answer']);
const questionBulk = json.results.map(q => q['question']);
setState({
data: json.results,
loading: false,
error: false,
});
setCorrectAnswers(correctAnswers.concat(correctAnswer));
setAllQuestions(allQuestions.concat(questionBulk));
})
.catch(err => {
setState({error: err})
})
}, [])
return (
<myContext.Provider
value={{
state, page, score, answers, right, wrong,
hitTrue: () => {setAnswers(answers.concat('True')); setPage(page + 1);},
hitFalse: () => {setAnswers(answers.concat('False')); setPage(page + 1);},
resetAll: () => {
setAnswers([]);
setPage(1);
setScore(0);
setRight([]);
setWrong([]);
clearScore();
clearWrongs();
clearRights();
},
calculateScore: () => calcScore(answers, correctAnswers),
updateScore: () => setScore(score + updatedScore),
updateRight: () => setRight(right.concat(rights)),
updateWrong: () => setWrong(wrong.concat(wrongs)),
showRightAnswers: () => {right.map((result, index) => {
return (
<p className="text-green-300 text-sm" key={index}>
+ {he.decode(`${allQuestions[result]}`)}
</p>)
})},
showWrongAnswers: () => {wrong.map((result, index) => {
return (
<p className="text-red-500 text-sm" key={index}>
- {he.decode(`${allQuestions[result]}`)}
</p>
)
})},
}}
>
{props.children}
</myContext.Provider>
);
}
export default ({ element }) => (
<Provider>
{element}
</Provider>
);
^the showRightAnswers() and showWrongAnswers() methods are the ones I am trying to figure out
and here is the results.js page.{context.showRightAnswers()} and {context.showWrongAnswers()} are where the mapped content is supposed to appear.
import React from 'react';
import Button from '../components/Button';
import { navigate } from 'gatsby';
import { myContext } from '../hooks/Provider';
const ResultsPage = () => {
return (
<myContext.Consumer>
{context => (
<>
<h1 className="">You Finished!</h1>
<p className="">Your score was {context.score}/10</p>
{context.showRightAnswers()}
{context.showWrongAnswers()}
<Button
buttonText="Try Again?"
buttonActions={() => {
context.resetAll();
navigate('/');
}}
/>
</>
)}
</myContext.Consumer>
);
}
export default ResultsPage;

You are returning inside your map, but you're not returning the map call itself - .map returns an array, and you have to return that array from your "show" functions, e.g.
showWrongAnswers: () => { return wrong.map((result, index) ...
^^^^
This will return the array .map generated from the showWrongAnswers function when it's called, and thus {context.showWrongAnswers()} will render that returned array

I am not able to make a React hooks toggle button to change between celcius and farenheit?

I want to toggle between Celcius and Fahrenheit with an onClick button on °C which can convert to Fahrenheit for my main.temp value max_temp and min_temp at the same time.
Weather.js
import React, { useState, useEffect } from 'react';
import Homepage from './Homepage';
function Weather() {
const API_KEY = 'b78ffacf63ad995ef34f6811b0e06433';
const [localweather, setLocalweather] = useState([]);
const [query, setQuery] = useState("");
//geolocation to get the local weather
const getLonLat = () => {
if (navigator.geolocation) {
navigator.geolocation.getCurrentPosition((position) => {
const lon = position.coords.longitude;
const lat = position.coords.latitude;
fetch(`https://api.openweathermap.org/data/2.5/weather?lat=${lat}&lon=${lon}&units=metric&appid=${API_KEY}`)
.then(response => response.json())
.then(result => {
setLocalweather(result)
return;
})
.catch(err => console.log(err));
})
}
}
useEffect(() => {
getLonLat();
}, [])
//give input to get other location weather
const searchInput = (e) => {
e.preventDefault()
fetch(`https://api.openweathermap.org/data/2.5/weather?q=${query}&units=metric&appid=${API_KEY}`)
.then(response => response.json())
.then(result => {
setLocalweather(result)
setQuery("")
})
.catch(err => console.log(err));
}
return (
<Homepage
localweather={localweather}
getLonLat={getLonLat}
searchInput={searchInput}
setQuery={setQuery} />
)
}
export default Weather;
Homepage.js
import React, { useState } from 'react';
function Homepage(props) {
return (
<div>
<h3>{props.localweather.main && props.localweather.main.temp} °C</h3>
<span>{props.localweather.main && props.localweather.main.temp_min} °C</span>
<span>{props.localweather.main && props.localweather.main.temp_max} °C</span>
</div>
)
}
export default Homepage;
I tried to put props.localweather.main && props.localweather.main.temp on a usestate() but it gives undefined.

Most probably your response from your API call is not an array, it will be an object. Also because the API call is asynchronous your localweather state won't have those properties immediately what you are looking for, that's why you got undefined error. Common practice to check for empty values with && in your render and not at useState to eliminate this issue.
First you need to change from [] to empty initial value {} in your useState as:
const [localweather, setLocalweather] = useState({});
Then you can have a null or undefined check as:
return (
{
props.localweather &&
props.localweather.main &&
<div>
<h3>{props.localweather.main.temp} °C</h3>
<span>{props.localweather.main.temp_min} °C</span>
<span>{props.localweather.main.temp_max} °C</span>
</div>
}
)