What is the way of preventing people using old Java Scripts?

[ahmetaa]

i think this is a big problem of Mozilla and NS6.x products. There are 
several pages i saw in the net they use old Java Script Code for 
"Browser dedection" like in

http://www.cizgi.com.tr/

They have the code:

  <script language=JavaScript> <!--
                           NS4 = (document.layers);
                           IE4 = (document.all);
                                  ver4 = (NS4 || IE4);
                                isMac = (navigator.appVersion.indexOf("Mac") != -1);
                                isMenu = ( IE4 && !isMac);

                        function popUp(){return};
                        function popDown(){return};
                        function startIt(){return};
                        if (!ver4) event = null;
                        //--> </SCRIPT>



i think this is the guilt of Netscape with "layer" aspect. Anyway, Point 
is what is the way of preventing people to use such code in their pages?

Thanks.