How to access web.config settings directly in .aspx page?

///////////////////  In your web config file

<appSettings>

<add key="Key" value="this is test" />

</appSettings>

///////////////// In aspx file

<asp:TextBox ID = "txtBox1" runat = "server" Text="<%=System.Configuration.ConfigurationManager.AppSettings["Key"]%>" />

///////////////////////////// for the variable

<script type="text/javascript">

   $(document).ready(function () {

        var my1 = '<%=ConfigurationManager.AppSettings["Key"].ToString() %>';

               alert(my1);

     });

</script>