关于js脚本动态创建Option对象问题

Question

我在程序中写了一段脚本，是需要把文本框中的对象添加到下拉框也就是Option对象。大家帮我看看这段脚本有问题吗？现在我出现的问题就是没有创建options对象。谢谢大家了./* ------  */function checktitle(obj){ 
    textBoxd = document.getElementById("ProjCost2_ascx_tkeys");
    var ddlId =document.getElementById("ProjCost2_ascx_DDLTitle");
    var drp = ddlId;
    var t=textBoxd;
    var j=0; 
    if(t.value=="")
    {
    }
     else
     { 
            for(var i=0;i<drp.length;i++)
            {
                  if(t.value==drp.options(i).text)
                  {
                       drp.value=drp.options(i).value; 
                       break;
                  }
                  else
                  {
                       j=j+1;
                  }
             }
            if(j==drp.length)
            {
                      var tOption = document.createElement("option");
                      tOption.text=t.value;
                      tOption.value=t.value;
                      drp.add(tOption);                                 }
      }
}

Answer 1

HTML代码也贴出来，方便别人测试呀

Answer 2

textBoxd = document.getElementById("ProjCost2_ascx_tkeys");
前面加个var

Answer 3

if(t.value==drp.options[i].text)
  {
  drp.value=drp.options[i].value;  
  break;
  }

Answer 4

我是用.NET开发的网站。HTML代码如下：    <td width="25%">
                                <asp:DropDownList ID="DDLTitle" runat="server" AppendDataBoundItems="True" 
                                    AutoPostBack="True" DataTextField="subname" DataValueField="task_id">
                                    <asp:ListItem Value="0">==请选择==</asp:ListItem>
                                </asp:DropDownList>
                                <asp:ScriptManager ID="ScriptManager1" runat="server" EnableScriptGlobalization="True">
                                </asp:ScriptManager>
                                <div>
                                    <asp:TextBox ID="tkeys" Style="z-index: 103; position: absolute;" runat="server"
                                        Font-Size="10" MaxLength="50"></asp:TextBox>
                                    <cc1:AutoCompleteExtender ID="aceName" runat="server" TargetControlID="tkeys" MinimumPrefixLength="1"
                                        ServicePath="~/WebService2.asmx" ServiceMethod="GetProductList">
                                    </cc1:AutoCompleteExtender>
                                </div>
                            </td>

Answer 5

<td width="25%">
  <asp:DropDownList ID="DDLTitle" runat="server" AppendDataBoundItems="True"  
  AutoPostBack="True" DataTextField="subname" DataValueField="task_id">
  <asp:ListItem Value="0">==请选择==</asp:ListItem>
  </asp:DropDownList>
  <asp:ScriptManager ID="ScriptManager1" runat="server" EnableScriptGlobalization="True">
  </asp:ScriptManager>
  <div>
  <asp:TextBox ID="tkeys" Style="z-index: 103; position: absolute;" runat="server"
  Font-Size="10" MaxLength="50"></asp:TextBox>
  <cc1:AutoCompleteExtender ID="aceName" runat="server" TargetControlID="tkeys" MinimumPrefixLength="1"
  ServicePath="~/WebService2.asmx" ServiceMethod="GetProductList">
  </cc1:AutoCompleteExtender>
  </div>
  </td>

Answer 6

function checktitle(obj){  
  textBoxd = document.getElementById("ProjCost2_ascx_tkeys");
  var ddlId =document.getElementById("ProjCost2_ascx_DDLTitle");
  var drp = ddlId;
  var t=textBoxd;
  var j=0;  
  if(t.value=="")
  {
  }
  else
  {  
  for(var i=0;i<drp.options.length;i++)
  {
  if(t.value==drp.options(i).text)
  {
  //drp.value=drp.options(i).value;  
  drp.selectedIndex = i;
  break;
  }
  else
  {
j=j+1;
  }
  }
  if(j==drp.options.length)
  {
  var tOption = document.createElement("option");
  tOption.text=t.value;
  tOption.value=t.value;
  drp.options.add(tOption);   
  }
  }
}