React JS Dynamically check if elements hit top of window

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8" />
  <script src="https://unpkg.com/react@17.0.2/umd/react.development.js"></script>
  <script src="https://unpkg.com/react-dom@17.0.2/umd/react-dom.development.js"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/babel-standalone/6.26.0/babel.min.js"></script>
</head>
<body>
  <div id="app"></div>
  <script type="text/babel">
    const { useState,useEffect,useRef } = React;
    function App() {
    const testRef = useRef(null);
      const [result, setResult] = useState('');

useEffect(() => {
        const handleScroll = () => {
          const itemOffset = testRef.current.offsetTop;
          const scrollTop = window.scrollY;

if (scrollTop >= itemOffset) {
            setResult('Item has reached the top');
          } else {
            setResult('');
          }
        };

window.addEventListener('scroll', handleScroll);

return () => {
          window.removeEventListener('scroll', handleScroll);
        };
      }, []);

return (
        <div className='container' style={{ height: '600px' }}>
          <div ref={testRef}>
            React JS Dynamically check if elements hit top of window
          </div>
          {result && <small className="result">{result}</small>}
        </div>
      );
    }
    ReactDOM.render(<App />, document.getElementById('app'));
  </script>

.result {
            font-size: 16px;
            color: #4CAF50;
            /* Green */
            position: fixed;
            left: 50%;
            transform: translateX(-50%);
            bottom: 20px;
            background-color: #333;
            color: #fff;
            padding: 12px;
            border-radius: 6px;
            z-index: 9999;

transition: opacity 0.3s ease-in-out;
        }
  </style>
</body>

</html>

 
<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8" />
  <script src="https://unpkg.com/react@17.0.2/umd/react.development.js"></script>
  <script src="https://unpkg.com/react-dom@17.0.2/umd/react-dom.development.js"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/babel-standalone/6.26.0/babel.min.js"></script>
</head>
<body>
  <div id="app"></div>
  <script type="text/babel">
    const { useState,useEffect,useRef } = React;
    function App() {
    const testRef = useRef(null);
      const [result, setResult] = useState('');
​
      useEffect(() => {
        const handleScroll = () => {
          const itemOffset = testRef.current.offsetTop;
          const scrollTop = window.scrollY;
​
          if (scrollTop >= itemOffset) {
            setResult('Item has reached the top');
          } else {
            setResult('');
          }
        };
​
        window.addEventListener('scroll', handleScroll);
​
        return () => {
          window.removeEventListener('scroll', handleScroll);
        };
      }, []);
​
      return (
        <div className='container' style={{ height: '600px' }}>
          <div ref={testRef}>
            React JS Dynamically check if elements hit top of window
          </div>
          {result && <small className="result">{result}</small>}
        </div>
      );
    }
    ReactDOM.render(<App />, document.getElementById('app'));
  </script>
​
  <style>
    .container {
      max-width: 800px;
      margin: 0 auto;
      padding: 20px;
      border-radius: 8px;
      box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
      text-align: center;
    }
​
   .result {
            font-size: 16px;
            color: #4CAF50;
            /* Green */
            position: fixed;
            left: 50%;
            transform: translateX(-50%);
            bottom: 20px;
            background-color: #333;
            color: #fff;
            padding: 12px;
            border-radius: 6px;
            z-index: 9999;
​
            transition: opacity 0.3s ease-in-out;
        }
  </style>
</body>
​
</html>