minimum app.js for illustration

blank-react-app;js

import './App.css';
import React,{Component} from 'react';

class App extends Component {
  constructor(){
    super();
   }
  
  render(){
   
    return (
      <div className="App">
             <h1>Welcome to App</h1>   
      </div>
    );
  }
}
export default App;