js控制多选框上下移动

<SELECT NAME="select1" id="select1" size=6>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
</SELECT>
<br><br>
<input type=button value=up onclick="goo(-1)">
<input type=button value=down onclick="goo(+1)">
<script language=javascript>
function goo(i)
{
var si = select1.selectedIndex;
var ops = select1.options;
if(si+i>=0 && ops[si+i] && ops[si]){
ops[si+i].swapNode(ops[si]);
}
}
</script>