The following code shows how to add alert message through Javascript code.
<!DOCTYPE html>
<html>
<head>
<script type='text/javascript'
src='http://code.jquery.com/jquery-1.9.1.js'></script>
<link rel="stylesheet" type="text/css"
href="http://netdna.bootstrapcdn.com/twitter-bootstrap/2.3.2/css/bootstrap-combined.no-icons.min.css">
<!--from w w w . java 2 s.c o m-->
<script type='text/javascript'>//<![CDATA[
$(window).load(function(){
function showAlert(message) {
$('#alert').html("<div class='alert alert-error'>"+message+"</div>");
$('#alert').show();
}
showAlert('Please have a look at the database.');
});
</script>
</head>
<body>
<div id='alert' class='hide'></div>
</body>
</html>