ListBox在客户端添加删除操作

<% @ Page language="c#" Codebehind="WebForm1.aspx.cs" AutoEventWireup="false" Inherits="WebExample.WebForm1"  %>
<! DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"  >
< HTML >
     < HEAD >
         < title > WebForm1 </ title >
         < meta  name ="GENERATOR"  Content ="Microsoft Visual Studio .NET 7.1" >
         < meta  name ="CODE_LANGUAGE"  Content ="C#" >
         < meta  name ="vs_defaultClientScript"  content ="JavaScript" >
         < meta  name ="vs_targetSchema"  content ="http://schemas.microsoft.com/intellisense/ie5" >
         < script >
           function Add()
           {
             var elemAll = document.getElementById("lbAll");
             var elemSel = document.getElementById("lbSel");
             for(var i=0;i<elemAll.options.length;i++)
             {
                 if(elemAll.options[i].selected)
                 { 
                     var SelText=elemAll.options[i].innerText;
                     var SelValue = elemAll.options[i].value;
                     var Num = elemSel.options.length;
                     elemSel.options[Num]=new Option(SelText,SelValue);
                     elemAll.options.remove(i);
                     i--;
                 }
             }
           }
           
           function Remove()
           {
              var elemAll = document.getElementById("lbAll");
             var elemSel = document.getElementById("lbSel");
             for(var i=0;i<elemSel.options.length;i++)
             {
                if(elemSel.options[i].selected)
                {
                    var SelText = elemSel.options[i].innerText;
                    var SelValue = elemSel.options[i].value;
                    var Num = elemAll.options.length;
                    elemAll.options[Num]= new Option(SelText,SelValue);
                    elemSel.options.remove(i);
                    i--;
                }
             }
           }
         </ script >
     </ HEAD >
     < body >
         < form  id ="Form1"  method ="post"  runat ="server" >
             < TABLE >
                 < TR >
                     < TD >
                         < asp:ListBox  id ="lbAll"  runat ="server"  Width ="100px"  Height ="150px"  SelectionMode ="Multiple" ></ asp:ListBox ></ TD >
                     < TD >
                         < INPUT  id ="btnAdd"  type ="button"  value =">>"  onclick ="Add();" >< br >
                         < INPUT  id ="btnRemove"  type ="button"  value ="<<"  onclick ="Remove();" >
                     </ TD >
                     < TD >
                         < asp:ListBox  id ="lbSel"  runat ="server"  Width ="100px"  Height ="150px"  SelectionMode ="Multiple" ></ asp:ListBox ></ TD >
                 </ TR >
             </ TABLE >
         </ form >
     </ body >
</ HTML >