alert function in javascript.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>alert Function</title>
</head>
<body>
    <!-- This function is used to display data in alert dialog box.
 alert really should be used only when you truly want to stop everything
 and let the user know something 
    -->
 <script>
    window.alert("hello");
 </script>
</body>
</html>