react-component-in-file.js

App.js

import React from 'react';
import ReactDOM from 'react-dom';

class Car extends React.Component {
  render() {
    return <h2>Hi, I am a Car!</h2>;
   
}
}

export default Car;

index.js

import React from 'react';
import ReactDOM from 'react-dom';
import Car from './App.js';

ReactDOM.render(<Car />, document.getElementById('root'));