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Div id is not defined in a function using react.js

import React from "react";
import "./profile.css";
const Notifications = () => {
function changeText() {
themebox.textContent =
"Nice";
}
function changeText2() {
themebox.textContent =
"Fair";
}
function changeText3() {
themebox.textContent = "Aggressive";
}
function changeText4() {
themebox.textContent =
"Threatening";
}
return (
<div className="notification-container">
<h3>Notifications</h3>
<div className="notif-picker">
<p className="Selected" onClick={changeText}>
Nice😘
</p>
<p onClick={changeText2}>Fair🕊</p>
<p onClick={changeText3}> Aggressive😈</p>
<p onClick={changeText4}>Threatening🤬</p>
</div>
<div className="theme-show-box">
<div className="theme-box" id="themebox"></div>
</div>
</div>
);
};
export default Notifications;
When i click on one of p tags it shows the text that i put in a function which is displayed in the div with classname "theme-box" and id "themebox". Everything seems to work fine, but i get an error in react saying themebox is not defined. Any idea how i can solve that error? :)

There's no variable named themebox in your javascript. Try this out instead, using react to manage state and functions to change the state on click.
// Get a hook function
const {useState} = React;
const Notifications = () => {
const [displayedText, setDisplayedText] = useState("");
const niceText = () => setDisplayedText("Nice");
const fairText = () => setDisplayedText("Fair");
const aggressiveText = () => setDisplayedText("Aggressive");
const threateningText = () => setDisplayedText("Threatening");
return (
<div className="notification-container">
<h3>Notifications</h3>
<div className="notif-picker">
<p className="Selected" onClick={niceText}>
Nice😘
</p>
<p onClick={fairText}>Fair🕊</p>
<p onClick={aggressiveText}> Aggressive😈</p>
<p onClick={threateningText}>Threatening🤬</p>
</div>
<div className="theme-show-box">
<div className="theme-box" id="themebox">{displayedText}</div>
</div>
</div>
);
};
// Render it
ReactDOM.createRoot(
document.getElementById("root")
).render(
<Notifications />
);
<div id="root"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/18.1.0/umd/react.development.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/18.1.0/umd/react-dom.development.js"></script>

React has it's own way of updating the DOM so it's generally a bad idea to try and manipulate the DOM directly. You should be using and updating state, and then using that state in the JSX.
By doing this you only really need one function which destructures the text content from the clicked element, and sets the state with that text. When the state changes that changed value is reflected in the JSX.
The (new) React documentation site has a good rundown on "how to think in React".
const { useState } = React;
function Example() {
// Initialise the state to an empty string
const [ text, setText ] = useState('');
// When any of the paragraphs is clicked
// destructure the textContent from that element
// and then set the state's new value. `e` is the
// event, and `target` is the element that fired the
// event ie. a paragraph element
function handleClick(e) {
const { textContent } = e.target;
setText(textContent);
}
return (
<div className="notification-container">
<h3>Notifications</h3>
<div className="notif-picker">
<p onClick={handleClick}>Nice 😘</p>
<p onClick={handleClick}>Fair 🕊</p>
<p onClick={handleClick}>Aggressive 😈</p>
<p onClick={handleClick}>Threatening 🤬</p>
</div>
<div className="theme-show-box">
<div className="theme-box">{text}</div>
</div>
</div>
);
}
ReactDOM.render(
<Example />,
document.getElementById('react')
);
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/17.0.2/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/17.0.2/umd/react-dom.production.min.js"></script>
<div id="react"></div>

How to create a React class for even and odd numbers

**I have a code that displays the news of the day. https://ibb.co/QMLY2Kx I have 10 classes named "block". Inside the "block" class there are two classes named "blockText". I need to get two different class names and not the same, I want to get this result "blockText1" and "blockText2". How to do it? **
import React from 'react';
import newsStyle from './News_module.css';
export class News extends React.Component {
render() {
const resultsRender = [];
for (var i = 0; i < this.props.news.length; i += 2) {
resultsRender.push(
<div class="block">
{
this.props.news.slice(i, i + 2).map((news, index) => {
return (
<div class="blockText" key={index}>
<p class="text">{news.title}</p>
{console.log(this.props.news.length)}
</div>
);
}
)
}
</div>
);
}
return (
<div>
<div className="headlineSecond">
<div className="Second">
{resultsRender}
</div>
</div>
</div>
);
}
}

You can use ternary operator for this . Here is an example where i chose the value of class based on the value of index and deciding upon whether it is even or odd
<div class={ index%2 ===0 ? "blockText1": "blockText2" } key={index}>
..... rest of code
</div>

How to render conditional with classNames with Reactjs

I am trying to use classNames to replace the conditional below in one line.
My problem is that i am not sure what is the right way to write the code because of the div etc...
I have the codes below :
conditional
const { pageTitle, removeTitle = false } = props; # destructuring
let result;
if(removeTitle){
result = <div className="header-without-title">{pageTitle}</div>;
} else {
result = <div className="header-with-title">{pageTitle}</div>;
}
return (<div className="result-title">{result});
};
If the div did not exist, i could write something like this...
const result = classNames({"header-without-title": removeTitle, "header-title": !removeTitle});
But i am not sure now that I have the div , I would appreciate some help here...
A solution outside of JSX would be very helpful

return (
<div className="result-title">
<div className={`header-${removeTitle ? 'without-title' : 'with-title'}`}>{pageTitle}</div>
</div>
);
or with use https://github.com/JedWatson/classnames
return (
<div className="result-title">
<div className={classNames({ 'header-without-title': removeTitle, 'header-with-title': !removeTitle })}>
{pageTitle}
</div>
</div>
);
EDIT:
A solution outside of JSX
const result = (
<div className={classNames({ 'header-without-title': removeTitle, 'header-with-title': !removeTitle })}>
{pageTitle}
</div>
);
return (
<div className="result-title">
{result}
</div>
);

You can just inline classNames function
const { pageTitle, removeTitle = false } = props;
const result = classNames({"header-without-title": removeTitle, "header-title": !removeTitle});
return (
<div className="result-title">
<div className={result}>
{pageTitle}
</div>
</div>);
);

There are several answers to this. Depends of each case
Ternary between two classes in React:
<div className={`header-${removeTitle ? 'without-title' : 'with-title'}`}>
Ternary between class or null in React Javascript:
<div className={removeTitle ? 'without-title' : null}>
Ternary between render class or not in React Javascript and Typescript:
<div className={...(removeTitle ? { className: 'without-title' } : {})}>

React JSX for loop shows only the last value

I have seen similar questions here, but these haven't been helpful so far.
I have a component that has an array state:
eventData: []
Some logic watches for events and pushes the objects to the state array:
eventData.unshift(result.args);
this.setState({ eventData });;
unshift() here is used to push the new elements to the top of the array.
What I want to achieve is rendering the content of the state array. I have written a conditional that checks for a certain state, and based on that state decides what to output.
let allRecords;
if (this.state.allRecords) {
for (let i = 0; i < this.state.eventData.length; i++) {
(i => {
allRecords = (
<div className="event-result-table-container">
<div className="result-cell">
{this.state.eventData[i].paramOne}
</div>
<div className="result-cell">
{() => {
if (this.state.eventData[i].paramTwo) {
<span>Win</span>;
} else {
<span>Loose</span>;
}
}}
</div>
<div className="result-cell">
{this.state.eventData[i].paramThree.c[0]}
</div>
<div className="result-cell">
{this.state.eventData[i].paramFour.c[0]}
</div>
<div className="result-cell">
{this.state.eventData[i].paramFive.c[0] / 10000}
</div>
<div className="result-cell-last">
{this.state.eventData[i].paramSix.c[0]}
</div>
</div>
);
}).call(this, i);
}
} else if (!this.state.allRecords) {
for (let i = 0; i < this.state.eventData.length; i++) {
if (this.state.account === this.state.eventData[i].paramOne) {
(i => {
allRecords = (
<div className="event-result-table-container">
<div className="result-cell">
{this.state.eventData[i].paramOne}
</div>
<div className="result-cell">
{() => {
if (this.state.eventData[i].paramTwo) {
<span>Win</span>;
} else {
<span>Loose</span>;
}
}}
</div>
<div className="result-cell">
{this.state.eventData[i].paramThree.c[0]}
</div>
<div className="result-cell">
{this.state.eventData[i].paramFour.c[0]}
</div>
<div className="result-cell">
{this.state.eventData[i].paramFive.c[0] / 10000}
</div>
<div className="result-cell-last">
{this.state.eventData[i].paramSix.c[0]}
</div>
</div>
);
}).call(this, i);
}
}
}
Problems that I have with this piece of code:
The code always renders the very last value of eventData state object.
I would like to limit the rendered elements to always show not more than 20 objects (the last 20 records of the state array).
paramTwo is a bool, and according to its value I expect to see either Win or Loose, but the field is empty (I get the bool value via the console.log, so I know the value is there)
Is this even the most effective way of achieving the needed? I was also thinking of mapping through the elements, but decided to stick with a for loop instead.
I would appreciate your help with this.

A few things :
First, as the comments above already pointed out, changing state without using setState goes against the way React works, the simplest solution to fix this would be to do the following :
this.setState(prevState => ({
eventData: [...prevState.eventData, result.args]
}));
The problem with your code here. Is that the arrow function was never called :
{() => {
if (this.state.eventData[i].paramTwo) {
<span>Win</span>;
} else {
<span>Loose</span>;
}
}
}
This function can be reduced to the following (after applying the deconstructing seen in the below code) :
<span>{paramTwo ? 'Win' : 'Lose'}</span>
Next up, removing repetitions in your function by mapping it. By setting conditions at the right place and using ternaries, you can reduce your code to the following and directly include it the the JSX part of your render function :
render(){
return(
<div> //Could also be a fragment or anything
{this.state.allRecords || this.state.account === this.state.eventData[i].paramOne &&
this.state.eventData.map(({ paramOne, paramTwo, paramThree, paramFour, paramFive, paramSix }, i) =>
<div className="event-result-table-container" key={i}> //Don't forget the key like I just did before editing
<div className="result-cell">
{paramOne}
</div>
<div className="result-cell">
<span>{paramTwo ? 'Win' : 'Lose'}</span>
</div>
<div className="result-cell">
{paramThree.c[0]}
</div>
<div className="result-cell">
{paramFour.c[0]}
</div>
<div className="result-cell">
{paramFive.c[0] / 10000}
</div>
<div className="result-cell-last">
{paramSix.c[0]}
</div>
</div>
)
}
</div>
)
}
Finally, to only get the 20 first elements of your array, use slice :
this.state.eventData.slice(0, 20).map(/* CODE ABOVE */)
EDIT :
Sorry, I made a mistake when understanding the condition you used in your rendering, here is the fixed version of the beginning of the code :
{this.state.allRecords &&
this.state.eventData.filter(data => this.state.account === data.paramOne).slice(0, 20).map(/* CODE ABOVE */)
Here, we are using filter to only use your array elements respecting a given condition.
EDIT 2 :
I just made another mistake, hopefully the last one. This should ahve the correct logic :
this.state.eventData.filter(data => this.state.allRecords || this.state.account === data.paramOne).slice(0, 20).map(/* CODE ABOVE */)
If this.state.allRecords is defined, it takes everything, and if not, it checks your condition.

I cleaned up and refactored your code a bit. I wrote a common function for the repetitive logic and passing the looped object to the common function to render it.
Use Map instead of forloops. You really need to check this this.state.account === this.state.eventObj.paramOne statement. This could be the reason why you see only one item on screen.
Please share some dummy data and the logic behind unshift part(never do it directly on state object), we'll fix it.
getRecord = (eventObj) => (
<React.Fragment>
<div className="result-cell">
{eventObj.paramOne}
</div>
<div className="result-cell">
{eventObj.paramTwo ? <span>Win</span> : <span>Loose</span>}
</div>
<div className="result-cell">
{eventObj.paramThree.c[0]}
</div>
<div className="result-cell">
{eventObj.paramFour.c[0]}
</div>
<div className="result-cell">
{eventObj.paramFive.c[0] / 10000}
</div>
<div className="result-cell-last">
{eventObj.paramSix.c[0]}
</div>
</React.Fragment>
)
render() {
let allRecords;
if (this.state.allRecords) {
allRecords = <div>{this.state.eventData.map(eventObj => this.getRecord(eventObj)}</div>;
} else if (!this.state.allRecords) {
allRecords = <div>{this.state.eventData.map(eventObj => {
if (this.state.account === this.state.eventObj.paramOne) {
return this.getRecord(eventObj);
}
return null;
})}</div>;
}
return (<div className="event-result-table-container">{allRecords}</div>);
}

How to Programmatically Assign and Get Refs in React

I was wondering if it is possible to programmatically assign and get refs in React. Suppose I wanted to go through a loop creating elements, giving them refs that consist of a name + an index. I know I can assign them like that using strings. However, the only way I know how to access refs consists of using this.refs.refname which, as far as I know, precludes me from doing something like this.refs.{refname + index}. Is there any way I can do something like this? The source code below should hopefully give you an idea of what I'm asking.
render = () => (<div className='row signature-group'>
<div className='col-md-1 col-xs-2'>
<b>{this.props.signerDescription}</b>
</div>
<div className='col-md-4 col-xs-7'>
{this.props.signers.map((signer, index) => <div className='text-with-line' key={index} ref={"sig" + index}>{signer}</div>)}
</div>
<div className='col-md-2 col-xs-3'>
{this.props.signers.map((signer, index) => {
return (index > 0 && this/*.refs.sig+index.value == whateverValue*/) ?
(<div className='text-with-line-long-name' key={index}>Date</div>) :
(<div className='text-with-line' key={index}>Date</div>);
})}
</div>
</div>)
Also, I've heard that using strings to assign refs is considered legacy. Is there any way to programmatically assign refs in a more up-to-date fashion?

Yes, you can use a ref callback to achieve this. The function passed as the ref attribute value will be passed the DOM node of the component once, after it is rendered:
applyRef = (index, ref) => {
this[`sig${index}`] = ref;
};
render = () => (
<div className="row signature-group">
<div className="col-md-1 col-xs-2">
<b>{this.props.signerDescription}</b>
</div>
<div className="col-md-4 col-xs-7">
{this.props.signers.map((signer, index) => (
<div className="text-with-line" key={index} ref={this.applyRef.bind(this, index)}>
{signer}
</div>
))}
</div>
<div className="col-md-2 col-xs-3">
{this.props.signers.map((signer, index) => {
return index > 0 && this[`sig${index}`].clientHeight > 0 ? (
<div className="text-with-line-long-name" key={index}>
Date
</div>
) : (
<div className="text-with-line" key={index}>
Date
</div>
);
})}
</div>
</div>
);
You can use bracket notation to create a new property on your class component (this) and then you access it with the same name (this.sig1, this.sig2).
String refs are deprecated and should no longer be used. Your refs are now applied directly to the component instance (this).