SO - 16913988

by Arun P Johny

HTML

<h2 class="x1">1</h2>
<h2 class="x2">2</h2>
<h2 class="x3">3</h2>
<h2 class="x4">4</h2>
<h2 class="x5">5</h2>

JavaScript

var el1 = $('.x4'), el2 = $('.x1'), el1prev = el1.prev();
el1.insertBefore(el2);
if(el1prev.length){
    el2.insertAfter(el1prev);
} else {
    el2.insertAfter($('h2').eq(0));
}