The following code shows how to create alert block with Javascript.
<!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">
<script type='text/javascript'
src="http://netdna.bootstrapcdn.com/twitter-bootstrap/2.3.2/js/bootstrap.min.js"></script>
<script type='text/javascript'>//<![CDATA[
$(window).load(function(){<!--from ww w . j a v a2 s .c o m-->
function showAlert(message, alertType) {
$('#alert').html("<div class='alert alert-"+alertType+"'>"+message+"</div>");
$('#alert').show();
}
showAlert('Alert.', 'success');
});//]]>
</script>
</head>
<body style='margin:30px'>
<div id='alert' class='hide'></div>
</body>
</html>