React Js Array fill Method

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8" />
    <script src="https://cdnjs.cloudflare.com/ajax/libs/react/17.0.2/umd/react.development.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/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">
        function App() {
            const array = [1, 2, 3, 4, 5];
            const startIndex = 2;
            const endIndex = 4;
            const value = 'Filled';
            array.fill(value, startIndex, endIndex);

return (
                <div className="container">
                    <h1>React Js Filling a portion of an existing array</h1>
                    <h2>Array: {array.join(', ')}</h2>

</div>
            );
        }

ReactDOM.render(<App />, document.getElementById("app"));
    </script>
    <style>
        * {
            box-sizing: border-box;
        }

.container {
            margin: 0 auto;
            width: 600px;
            text-align: center;
            box-shadow: 0 1px 2px 0 rgba(0, 0, 0, 0.12), 0 2px 4px 0 rgba(0, 0, 0, 0.24);
            padding: 20px;
        }

h1 {
            font-size: 24px;
            color: #333;
        }

h2 {
            font-size: 18px;
            color: #666;
            margin-top: 10px;
        }

</style>
</body>

</html>