Edit in JSFiddle

$(document).ready(function(){
    var iCount = $('.dummy').length;
    var eCount = $('div').length;
    
    $('span').html('<br/>Number of div elements are : <b>' + eCount + '</b><br/> Number of elements with class dummy are : <b>' + iCount + '</b>');
});

<div> div 1 </div>
<div> div 2 </div>
<div> div 3 </div>
<br/>
<p class="dummy"> Para 1 </p>
<p class="dummy"> Para 2 </p>
<p class="dummy"> Para 3 </p>
<p class="dummy"> Para 4 </p>

<span></span>