Allow only decimal numbers in the Textbox using Javascript

Javascript code:

    <script language="Javascript" type="text/javascript">
        function onlyNos(e, t) {
            try {
                if (window.event) {
                    var charCode = window.event.keyCode;
                }
                else if (e) {
                    var charCode = e.which;
                }
                else { return true; }
                if (charCode > 31 && (charCode < 48 || charCode > 57)) {
                    if (charCode === 46)
                        return true;
                    else
                        return false;
                }
                return true;
            }
            catch (err) {
                alert(err.Description);
            }
        }
    </script>

Textbox:

<asp:TextBox ID="txtNumbersOnly" runat="server" onkeypress="return onlyNos(event,this);" Width="146px" CssClass="rightinput"></asp:TextBox>