jQuery 獲取單選按鈕radio 已選中的值

<div id="wrap">
                <input type="radio" name="aa" value="1" id="xz1" />
                <input type="radio" name="aa" value="2" id="xz2" />
 </div>

 

js:

var sss = $('#wrap input[name="aa"]:checked ').val();