Why can't work with the file system on node js?

Question

Node.js

I work with create-react-app, when I try to create, read and other operations with files, it generates an error:

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

// components 
import Sidebar from './components/Sidebar/Sidebar.js'


// data
let webComponents = require('./data/web-components.json');

const fs = require('fs');

console.log(fs);


setTimeout(() => {
  webComponents.push({'text': 'четвертый', 'isActive': false});

  fs.readFile('./data/web-components.json', 'JSON.stringify(webComponents)', () => console.log('ok'));
}, 4000);

class App extends React.Component {

  constructor() {
    super();
  }
 
  render() {
     return (
        <div className='App'>
          <Sidebar items={webComponents} />
        </div>
      );
  }
}

export default App;

Answer 1

A simple web server is launched in the node, which gives the react application to the browser.
React runs on the client, it has nothing to do with the node.