JS的左移和右移1

<script language="JavaScript">
<!--
function moveOption(e1, e2){
try{
for(var i=0;i<e1.options.length;i++){
if(e1.options[i].selected){
var e = e1.options[i];
e2.options.add(new Option(e.text, e.value));
e1.remove(i);
i=i-1
}
}
document.myform.city.value=getvalue(document.myform.list2);
}
catch(e){}
}
function getvalue(geto){
var allvalue = "";
for(var i=0;i<geto.options.length;i++){
allvalue +=geto.options[i].value + ",";
}
return allvalue;
}
function changepos(obj,index){
if(index==-1){
if (obj.selectedIndex>0){
obj.options(obj.selectedIndex).swapNode(obj.options(obj.selectedIndex-1))
}
}else if(index==1){
if (obj.selectedIndex<obj.options.length-1){
obj.options(obj.selectedIndex).swapNode(obj.options(obj.selectedIndex+1))
}
}
}
//-->
</script>
HTML代码片段
<form method="post" name="myform">
<table border="0" width="300">
<tr>
<td width="40%">
<select style="WIDTH:100%" multiple name="list1" size="12" ondblclick="moveOption(document.myform.list1, document.myform.list2)">
<option value="北京">北京</option>
<option value="上海">上海</option>
<option value="山东">山东</option>
<option value="安徽">安徽</option>
<option value="重庆">重庆</option>
<option value="福建">福建</option>
<option value="甘肃">甘肃</option>
<option value="广东">广东</option>
<option value="广西">广西</option>
<option value="贵州">贵州</option>
<option value="海南">海南</option>
<option value="河北">河北</option>
<option value="黑龙江">黑龙江</option>
</select>
</td>
<td width="20%" align="center">
<input type="button" value="添加" onclick="moveOption(document.myform.list1, document.myform.list2)"><br/>
<br/>
<input type="button" value="删除" onclick="moveOption(document.myform.list2, document.myform.list1)">
</td>
<td width="40%">
<select style="WIDTH:100%" multiple name="list2" size="12" ondblclick="moveOption(document.myform.list2, document.myform.list1)">
</select>
</td>
<td>
<button onclick="changepos(list2,-1)" type="button">上移</button>
<br/>
<button onclick="changepos(list2,1)" type="button">下移</button>
</td>
</tr>
</table>
值：<input type="text" name="city" size="40">
</form>