Question

I’d like to know the number of element with myclass as CSS name are in the value result

$.ajax({
    url: 'Home/Index',
    type: 'POST',
    data: id : 5,
    success: function (data) {

        //get number of myclass here


    }
});

I tried this :
$('.myclass', data).length; but I get 0 all the time

Update1
Output console :

<div class="ui-widget myclass">
    <div class="ui-state-error ui-corner-all" style="padding: 0 .7em;"> 
        <p><span id="iconAlert" class="ui-icon ui-icon-alert" style="float: left; margin-right: .3em;"></span> 
        <strong>Alert:</strong> Sample ui-state-error style.</p>
    </div>
</div>

Answer 1

Assuming I’ve understood your question correctly, you need to use filter:

$(data).filter(".myclass");

Your current attempt is equivalent to $(data).find(".myclass") and since find looks at descandants it won’t find any elements at the top level. filter on the other hand, will.