如何让select下拉框随着内容改变大小

<select name="aa" onchange="resetSelectWidth(this);">

<option value="111">111</option>

<option value="222">22222</option>

<option value="333">33333333</option>

<option value="444">44444444444</option>

<option value="555">555555555555555</option>

</select>



<script>

function resetSelectWidth(obj){

var tempObj=document.createElement("select");

tempObj.length=1;

tempObj.options[0].text=obj.options[obj.selectedIndex].text

obj.parentNode.appendChild(tempObj);

obj.style.width=tempObj.offsetWidth;

obj.parentNode.removeChild(tempObj);

}



</script>