:only-child Selector
Selects all elements that are the only child of their parent.
.only-child()
If the parent has other child elements, nothing is matched.
Change the text and add a border for each button that is the only child of its parent.
JS
<div>
<button>Sibling!</button>
<button>Sibling!</button>
</div>
<div>
<button>Sibling!</button>
</div>
<div>None</div>
<div>
<button>Sibling!</button>
<button>Sibling!</button>
<button>Sibling!</button>
</div>
<div>
<button>Sibling!</button>
</div>
CSS
div {
width: 100px;
height: 80px;
margin: 5px;
float: left;
background: #b9e;
}
HTML
$("div button:only-child").text("Alone").css("border", "2px blue solid");
DEMO