:only-of-type Selector

only-of-type ( ) version added: 1.9

Description: Selects all elements that have no siblings with the same element name.

If the parent has other child elements with the same element name, nothing is matched.

Examples:

Example: Change the text and add a border for each button that is the only child button of its parent. 

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>css demo</title>

  <style>

  div {
    width: 100px;
    height: 80px;
    margin: 5px;
    float: left;
    background: #b9e;
  }
  span {
    padding: 2px;
    margin: 3px;
    line-height: 1.4;
    border: 1px solid #000;
  }

  </style>

  <script src="//code.jquery.com/jquery-1.10.2.js"></script>
</head>
<body>
  

<div>
  <button>Sibling!</button>
  <button>Sibling!</button>
</div>

<div>
  <button>Sibling!</button>
</div>
<div>
  None
</div>

<div>
  <button>Sibling!</button>
  <span>Sibling!</span>
  <span>Sibling!</span>
</div>

<div>
  <button>Sibling!</button>
</div>

<script>

  $( "button:only-of-type" ).text( "Alone" ).css( "border", "2px blue solid" );

</script>

  
</body>
</html>

Demo: