JavaScript alert demo

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
  <script type="text/javascript">
  <!--
  function show_alert()
  {
  alert("I am an alert box!");
  }
  //-->
  </script>
  <title>JavaScript alert demo</title>
</head>
<body>
  <form>
    <input type="button" onclick="show_alert()" value="Show alert box" />
  </form>
</body>
</html>