Update React page in class-based component without using useState.

Question

I'm using React's class-based component to display all the tokens first. Then I want to display two texts with spanid at the same time, regardless of the order, using the previous and next buttons to re-render the page. There will be n*(n-1) possibilities for re-rendering the page. This is because the first text with a spanid will be paired with the second text with another spanid, up to the n-1th token with a spanid. For n pieces of text with spanid, the page can be re-rendered n*(n-1) times using the previous/next buttons. Since I'm writing code using React's class-based components, I'm not sure how to handle this using useState and props like I would in a functional setup. Any help on this issue is greatly appreciated.

import React from 'react';
import './App.css';

const record = [
  { "tid": 1, "token_text": "Canis Familiaris", "spanid": 1, "label": "Name" },
  { "tid": 2, "token_text": "is" },
  { "tid": 3, "token_text": "the" },
  { "tid": 4, "token_text": "scientific name", "spanid": 2, "label": "name type" },
  { "tid": 5, "token_text": "of" },
  { "tid": 6, "token_text": "dog", "spanid": 3, "label": "species" },
  { "tid": 7, "token_text": "." }
];

class Relation extends React.Component {
const input_tokens = record;
var cntr = 200;

   input_tokens.forEach(tk => {
       const span = tk['spanid'];
       if (!tk['spanid']) {
           tokens_to_render.push(
            <div key= {`id${cntr}`} >
               <div id = {`label${cntr}`} className='no-label' key={tk.tid}>--</div>
               <div key={cntr} id = {`span${cntr}`} index={tk['spanid']} >
                   {tk['token_text']}
              </div>
            </div>
          );
          
       } else {
          tokens_to_render.push(
            <div key = {`id${cntr}`} >
              <div id = {`label${cntr}`} className='label' key={tk.tid} >{tk['label']}</div>
              <div
                key={cntr} id = {`span${cntr}`}
                index={tk['spanid']}
              >
                  {tk['token_text']}
              </div>
            </div>
          );
       };
       cntr = cntr 1;
  });
return (
        <div key="outer" >
          <div key="id" className="control-box">
             {tokens_to_render}
             
      </div>

    </div>
  )
}
  }
export default Relation;

Answer 1

Translation: Hooks like useState can only be used in function components. To use state in a class component:

• Return the JSX to be displayed from the render() method.
• Assign the initial state to the state attribute.
• Call this.setState to update the status.

For example:

class Example extends React.Component {
    state = {
        count: 0
    }
    
    render() {
        return <div>
            <button onClick={() => this.setState({count: this.state.count + 1})}>
                Increment count
            </button>
            <p>Clicked {this.state.count} times</p>
        </div>;
    }
}