Textbox onkeyup fonksiyonu dropdownlist item seçme

Dropdownlist item Textbox Onkeyup Fonksiyonu

SqlDatasoıurce ile
<asp:DropDownList ID="ddMusteri" CssClass="form-control" runat="server" DataSourceID="ddMusteriSqlDataSource" DataTextField="MUSTERI_ADI" DataValueField="MUSTERI_ADI" AutoPostBack="true" OnSelectedIndexChanged="ddMusteri_SelectedIndexChanged" OnDataBound="ddMusteri_DataBound"></asp:DropDownList>
                 <asp:SqlDataSource ID="ddMusteriSqlDataSource" runat="server" ConnectionString="<%$ ConnectionStrings:musteriCS %>" SelectCommand="SELECT DISTINCT  MUSTERI_ADI  FROM WEB_MUSTERI"></asp:SqlDataSource>


İtem ile
<asp:TextBox ID="txtSearch" runat="server"
         onkeyup = "FilterItems(this.value)"></asp:TextBox><br />
    <asp:DropDownList ID="ddlItems" runat="server" >
        <asp:ListItem Text="Mango" Value="1"></asp:ListItem>
        <asp:ListItem Text="Orange" Value="2"></asp:ListItem>
        <asp:ListItem Text="Apple" Value="3"></asp:ListItem>
        <asp:ListItem Text="Banana" Value="4"></asp:ListItem>
        <asp:ListItem Text="Water Melon" Value="5"></asp:ListItem>
        <asp:ListItem Text="Lemon" Value="6"></asp:ListItem>
        <asp:ListItem Text="Pineapple" Value="7"></asp:ListItem>
        <asp:ListItem Text="Papaya" Value="8"></asp:ListItem>
        <asp:ListItem Text="Chickoo" Value="9"></asp:ListItem>
        <asp:ListItem Text="Apricot" Value="10"></asp:ListItem>
        <asp:ListItem Text="Grapes" Value="11"></asp:ListItem>
        <asp:ListItem Text="Olive" Value="12"></asp:ListItem>
        <asp:ListItem Text="Guava" Value="13"></asp:ListItem>
        <asp:ListItem Text="Sweet Lime" Value="14"></asp:ListItem>
    </asp:DropDownList>
    <br />
    <asp:Label ID="lblMessage" runat="server" Text=""></asp:Label>

Javascript Kodu
<script type = "text/javascript">
        var ddlText, ddlValue, ddl, lblMesg;
        function CacheItems() {
            ddlText = new Array();
            ddlValue = new Array();
            ddl = document.getElementById("<%=ddMusteri.ClientID %>");
            <%--lblMesg = document.getElementById("<%=lblMessage.ClientID%>");--%>
            for (var i = 0; i < ddl.options.length; i++) {
                ddlText[ddlText.length] = ddl.options[i].text;
                ddlValue[ddlValue.length] = ddl.options[i].value;
            }
        }
        window.onload = CacheItems;

        function FilterItems(value) {
            ddl.options.length = 0;
            for (var i = 0; i < ddlText.length; i++) {
                if (ddlText[i].toLowerCase().indexOf(value) != -1) {
                    AddItem(ddlText[i], ddlValue[i]);
                }
            }
            lblMesg.innerHTML = ddl.options.length + " items found.";
            if (ddl.options.length == 0) {
                AddItem("No items found.", "");
            }
        }

        function AddItem(text, value) {
            var opt = document.createElement("option");
            opt.text = text;
            opt.value = value;
            ddl.options.add(opt);
        }
</script>