例题 从这复制到那边

<select id="aa" style=" width:200px; height:200px"size="10">
<option >123</option>
<option>234</option>
<option>345</option>
<option>355</option>
</select>
<input id="q" type="button" value="单移" onclick="DY()"/>
<input id="W" type="button" value="全部移" onclick="QY()"/>
<select id="bb" style=" width:200px; height:200px"size="10">
</select>
<script type="text/javascript">
function DY()
{ var M=document.getElementById("aa");
var J= M.value;
var h="<option class=‘of‘>"+J+"</option>";
var attr=document.getElementsByClassName("of")
var cf=true;
for(var i=0;i<attr.length;i++)
{ if(attr[i].innerHTML==J)
{ cf=false;
break;}
}
if(cf)
{ var P=document.getElementById("bb");
P.innerHTML+=h;}
} ;
function QY()
{document.getElementById("bb").innerHTML=document.getElementById("aa").innerHTML;

}