Copy TextBox Text to Clipboard in ASP.Net

Hi,

I using GridView with TextBox controls.

I need click on the button to copy the text from the text field and paste the text (e.g. ctrl+v) using C# ASPNET

This is the tutorial

I don't have error but the copy not working.

Help me to do it.

My code below

    <script type="text/javascript">
        function myFunction() {
            /* Get the text field */
            var copyText = document.getElementById("txcp");

            /* Select the text field */
            copyText.select();
            copyText.setSelectionRange(0, 99999); /* For mobile devices */

            /* Copy the text inside the text field */
            document.execCommand("copy");

            /* Alert the copied text */
            alert("Copied the text: " + copyText.value);
        }
    </script>    

                    <asp:TemplateField HeaderText="Annotation" ItemStyle-HorizontalAlign="Left">
                        <ItemTemplate>
                            <asp:TextBox ID="txcp" runat="server"
                                Width="100%" TextMode="MultiLine"
                                ClientID="txcp" ClientIDMode="Static"
                                Text='<%# Eval("tAnnotation").ToString() %>'
                                CssClass="ddl_Class_new"></asp:TextBox>
                            <asp:Button ID="btncopy" runat="server" Text="Copy text" OnClientClick="myFunction();" />
                        </ItemTemplate>
                    </asp:TemplateField>