componentClass.js

class App extends React.Component {
  
  state = { clicked: false, initialized: false };

  componentDidMount() {
    this.setState({ initialized: true });
  }

  setClicked = () => {
    this.setState({ clicked: true });
  }


  render() {
    const { initialized, clicked } = this.state;

    return (
      <div className="App">
        {initialized && <h1>Initialized</h1>}
        <h1 onClick={() => this.setClicked(true)}>Please click me!</h1>
        {clicked && <h2>You clicked an object!</h2>}
      </div>
    );
  }
}