多选框选择后在另外一个多选框显示。

<script>
 function add( fromCtrl , toCtrl ){
  for( i=0 ;i<fromCtrl.length ;i++){
   if( fromCtrl.options[i].selected == true)
   {
    //alert(fromCtrl.options[i].value);
    for( j=0 ;j<toCtrl.length;j++)
    {
     if( fromCtrl.options[i].value == toCtrl.options[j].value )
     {
      alert("已经添加了"+fromCtrl.options[i].value);
      return ;
     }
    }
    // add item
    toCtrl.options[toCtrl.length] = new Option(fromCtrl.options[i].name,fromCtrl.options[i].value);
    
    }
  }
 }
 
 function deleteItem( toCtrl ){
  j=0 ;
  count = toCtrl.length;
  
  for( i=0 ;i< count ;i++){
   if( toCtrl.options[i-j].selected == true){
    toCtrl.remove(i-j);
    j++;
   }
  }
 
 }
 
</script>
<form name="myform">
 <select name="fromsel" multiple="true" size=6>
  <option name="a" value="va">a</option>
  <option name="b"  value="vb">b</option>
  <option name="c" value="vc">c</option>
  </select>
  <select name="tosel" multiple="true" size=6/>
  <input type="button" value="add" onclick="add(document.myform.fromsel,document.myform.tosel)"/>
  <input type="button" value="delete" onclick="deleteItem(document.myform.tosel)"/>
</form>