how to use a js class in react

class App extends Component {
    constructor() {
        super()
        this.state = {
            name: "Sally",
            age: 13
        }
    }
    
    render() {
        return (
            <div>
                <h1>{this.state.name}</h1>
                <h3>{this.state.age} years old</h3>
            </div>
        )    
    }
}class Developer {  constructor(firstname, lastname) {    this.firstname = firstname;    this.lastname = lastname;  }   getName() {    return this.firstname + ' ' + this.lastname;  }} class ReactDeveloper extends Developer {  getJob() {    return 'React Developer';  }} var me = new ReactDeveloper('Robin', 'Wieruch'); console.log(me.getName());console.log(me.getJob());