React Js Check First Letter of String is Uppercase

<!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://unpkg.com/@babel/standalone@7.14.7/babel.min.js"></script>
</head>
<body>
  <div id="app"></div>
  <script type="text/babel">
    const { useState } = React;
    function App() {
      const str = "hello, world!"; // Replace with your string

const isFirstLetterUppercase = str => {
        if (str.length === 0) {
          return false;
        }
        const firstCharCode = str.charCodeAt(0);
        return firstCharCode >= 65 && firstCharCode <= 90;
      };

const modifiedString = capitalizeFirstLetter(str);
      return (
        <div className='container'>
          <h3 className='title'> use charCodeAt() Method</h3>
          <p className='string-info'>String: {str}</p>
          <p className='uppercase-check'>Is the first letter uppercase? {isFirstLetterUppercase(str).toString()}</p>
          <p className='modified-string'>Modified String: {modifiedString}</p>
        </div>

);
    }
    ReactDOM.render(<App />, document.getElementById("app"));
  </script>

.title {
      font-size: 24px;
      color: #333;
      margin: 0;
      padding-bottom: 10px;
    }

.string-info,
    .uppercase-check,
    .modified-string {
      font-size: 18px;
      color: #555;
      margin: 10px 0;
    }

.modified-string {
      color: #00a0e4;
    }
  </style>
</body>

</html>