No Alphabet JavaScript

function noAlphabet(e)
{
           var regex = new RegExp("[0-9]");
           var key = e.keyCode || e.which;
           key = String.fromCharCode(key);

           if (!regex.test(key))
           {
               e.returnValue = false;
               if (e.preventDefault)
               {
                   e.preventDefault();
               }
           }
}

<asp:TextBox ID="qty" runat="server" CssClass="form-control" onkeypress="return noAlphabet(event)" MaxLength="3"></asp:TextBox>