两侧SELECT列表值的添加与移除

<form name=form1>
<table border="0" cellspacing="5" cellpadding="5" align="center">
<tr>
<td>
<div align="center">
<select id=list1 multiple size=8 onClick="seladdchk();" name="select2">
<option value="A">a</option>
<option value="B">b</option>
<option value="C">c</option>
<option value="D">d</option>
<option value="E">e</option>
<option value="F">f</option>
<option value="G">g</option>
<option value="H">h</option>
</select>
</div>
</td>
<td>
<div align="center">
<input name=add type=button value="添加>>" onClick="MoveToRight(this.form.list1, this.form.list2);" disabled>
<br>
<input name=sub type=button value="移除<<" onClick="Remove(this.form.list2);" disabled>
</div>
</td>
<td>
<div align="center">
<select id=list2 multiple size=8 onClick="selsubchk();" name="select">
</select>
</div>
</td>
</tr>
</table>
</form>

<script language="JavaScript">
<!--
function seladdchk()
{
document.all.add.disabled=false
}

function selsubchk()
{
document.all.sub.disabled=false
}

function MoveToRight(e1, e2)
{
var e = e1.options
var o2 = e2.options
var msg
msg=''

for(i=e.length-1;i>=0;i--)
{
if(e[i].selected)
{
for (j=o2.length-1;j>=0;j--)
{
if(e[i].text == o2[j].text && e[i].value == o2[j].value)
{
msg=msg+e[i].text;
}
}

if (msg=='')
{
e2.options.add(new Option(e[i].text, e[i].value));
}
else
{
alert(msg+'已经选择!');
return false;
}
}
}
}

function Remove(e2)
{
var e = e2.options
for(i=e.length-1;i>=0;i--)
{
if(e[i].selected)
{
e2.options.remove(i);
document.all.sub.disabled=true;
}

}
}
//-->
</script>