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HTML

              
                 <div id="root"></div>
              
            
!

CSS

              
                
              
            
!

JS

              
                const { MouseEvent, useRef, useEffect, Component, useState } = React;

// Function component example
const App = () => {
  // Call setTimout after component mounts
  useEffect(() => {
    const timer = setTimeout(() => console.log('Initial timeout!'), 1000);
    return () => clearTimeout(timer);
  }, []);

  // Call setTimeout on user interaction
  const timerRef = useRef(null);
  const sendMessage = (e: MouseEvent<HTMLButtonElement>) => {
    e.preventDefault();
    timerRef.current = setTimeout(() => alert('Hey 🎉'), 1000);
  }

  useEffect(() => {
    // Clear the interval when the component unmounts
    return () => clearTimeout(timerRef.current);
  }, []);

  return (
    <button onClick={sendMessage}>
      Send message
    </button>
  );
}

/*
// Class component example
class App extends Component {
  timer;
  sendMessage = (e) => {
    e.preventDefault();
    this.timer = setTimeout(() => alert('Hey 🎉'), 1000);
  }
  
  componentWillUnmount() {
    clearTimeout(this.timer);
  }
  
  render() {
    return (
      <button onClick={this.sendMessage}>
        Send message
      </button>
    );
  }
}
*/

// Wrapper for mounting / unmounting the App component
const Wrapper = () => {
  const [showApp, setShowApp] = useState(true);
  const toggleShowApp = () => {
    setShowApp((prevValue) => !prevValue);
  };

  return (
    <>
      <button onClick={toggleShowApp}>{showApp ? 'Hide' : 'Show'} App component</button>
      <br />
      <br />
      {
        showApp && <App />
      }
    </>
  );
}

ReactDOM.render(<Wrapper />, document.getElementById('root'));
              
            
!
999px

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