Code for adding a css class to an element?

$('#' + id + ' a').addClass('jq4ubutton');
$('#' + id + ' .clickmsgbtn').bind('click', function (e) {
    e.preventDefault();
    $(this).after( & amp; quot; & lt; span class = 'clickmsg'
    style = 'color:green;margin-left:5px;' & gt; Click! & lt;
    /span>");
                        $('#'+id+' .clickmsg').fadeIn('slow').delay(1000).fadeOut('slow').empty();
                    });