This version of the client sniffer code is object oriented but contains a "safety check" to work around a bug of  Internet Explorer 3.x on the Macintosh. If you create an "is" object on IE3 for the Mac, the first time the page is loaded, the code will work fine, however any reloads of the page will cause the browser to crash. To get around this on IE3 for the Mac, we don't create an "is" object; instead, we create a Boolean variable called "isIE3Mac", which is set to true when the page is loaded into Internet Explorer 3 for the Mac OS.

One thing to be aware of: when checking the "navigator.appVersion" property, you'll notice on the Windows side that Internet Explorer 3.0 says it's Navigator 2.0, and thus the "navigator.appVersion" property returns a "2." On the Macintosh, Internet Explorer 3.0 says it's Navigator 3.0, and "navigator.appVersion" will return a "3".

When optimizing a page for multiple browsers, it is sometimes convenient to check the browser vendor and/or version and then use document.write() statements in <SCRIPT> elements in the page's BODY to dynamically generate HTML markup which is optimized for the current browser. Here is an example of the code necessary to dynamically generate vendor- or version-specific HTML markup. This code uses the "is" object defined by the sample JavaScript code below to check browser vendor and version. Don't forget, however, to first check the boolean variable "isIE3Mac" to see if that's true or not. The reason we check it first is because if "isIE3Mac" is true, then the "is" object doesn't actually exist, and we don't want the script to fail with an error on IE3 for the Mac.

<SCRIPT>
<!--
if (!isIE3Mac && is.gecko) {
  {
   // document.write() statements to create markup for user agents implementing Gecko layout engine
  }
  else if  (!isIE3Mac && is.nav4) {
  {
   // document.write() statements to create markup for Navigator 4
  }
  else if (!isIE3Mac && is.ie5up)
  {
   // document.write() statements to create markup for IE 4 and later versions
  }
  else
  {
   // document.write() statements to create static HTML markup for earlier versions
  }
}
// -->
</SCRIPT>

In your page's core JavaScript functions, you can then have vendor- and version-specific code forks where necessary. These code forks reference objects, properties, methods, and functions which are only available in specific browser versions. The code forks may also reference HTML page elements whose HTML markup is dynamically generated only for certain browser versions.

This code fragment also uses the "is" object, and the "isIE3Mac" boolean defined by the sample JavaScript code below to check browser vendor and version.

if (!isIE3Mac && is.gecko)
{
   // JavaScript here for user agents implementing Gecko layout engine

}
else if  (!isIE3Mac && is.nav4)
{
   // JavaScript here for Navigator 4
}
else if (!isIE3Mac && is.ie5up)
{
   // JavaScript here for IE 4 and later
}
else if (!isIE3Mac && (is.nav3 || is.opera))
{
   // JavaScript here for Nav3 and Opera 
}
else 
{
   // JavaScript here for Nav2 and IE 3 
}

Here is the JavaScript code necessary to detect browser vendor, version number, and operating system. This code creates an object called "is" which has properties indicating the browser's vendor, version number, JavaScript version, and operating system.

This code is believed to be compatible with all versions of all JavaScript-capable browsers on all platforms. It has been tested on the following operating systems and browser versions:

• Windows NT:  Navigator 4, Navigator 3, and Navigator 2; Internet Explorer 5; Internet Explorer 3; Opera 3
• Windows 98: Netscape 6;Navigator 4.76; Internet Explorer 4; Internet Explorer 5; Internet Explorer 5.5; Opera 5; HotJava 3
• Macintosh: Navigator 4, Internet Explorer 3.01, Internet Explorer 4.02
• RedHat Linux 6.2: Navigator 4.6; Netscape 6
• SunOS5: Navigator 3

<--
// Ultimate client-side JavaScript client sniff. Version 3.03
// (C) Netscape Communications 1999.  Permission granted to reuse and distribute.
// Revised 17 May 99 to add is.nav5up and is.ie5up (see below).
// Revised 21 Nov 00 to add is.gecko and is.ie5_5 Also Changed is.nav5 and is.nav5up to is.nav6 and is.nav6up
// Revised 22 Feb 01 to correct Javascript Detection for IE 5.x, Opera 4, 
//                      correct Opera 5 detection
//                      add support for winME and win2k
//                      synch with browser-type-oo.js
// Revised 26 Mar 01 to correct Opera detection
// Revised 02 Oct 01 to add IE6 detection

// Everything you always wanted to know about your JavaScript client
// but were afraid to ask ... "Is" is the constructor function for "is" object,
// which has properties indicating:
// (1) browser vendor:
//     is.nav, is.ie, is.opera, is.hotjava, is.webtv, is.TVNavigator, is.AOLTV
// (2) browser version number:
//     is.major (integer indicating major version number: 2, 3, 4 ...)
//     is.minor (float   indicating full  version number: 2.02, 3.01, 4.04 ...)
// (3) browser vendor AND major version number
//     is.nav2, is.nav3, is.nav4, is.nav4up, is.nav6, is.nav6up, is.gecko, is.ie3, 
//     is.ie4, is.ie4up, is.ie5, is.ie5up, is.ie5_5, is.ie5_5up, is.ie6, is.ie6up, is.hotjava3, is.hotjava3up
// (4) JavaScript version number:
//     is.js (float indicating full JavaScript version number: 1, 1.1, 1.2 ...)
// (5) OS platform and version:
//     is.win, is.win16, is.win32, is.win31, is.win95, is.winnt, is.win98, is.winme, is.win2k
//     is.os2
//     is.mac, is.mac68k, is.macppc
//     is.unix
//     is.sun, is.sun4, is.sun5, is.suni86
//     is.irix, is.irix5, is.irix6
//     is.hpux, is.hpux9, is.hpux10
//     is.aix, is.aix1, is.aix2, is.aix3, is.aix4
//     is.linux, is.sco, is.unixware, is.mpras, is.reliant
//     is.dec, is.sinix, is.freebsd, is.bsd
//     is.vms
//
// See http://www.it97.de/JavaScript/JS_tutorial/bstat/navobj.html and
// http://www.it97.de/JavaScript/JS_tutorial/bstat/Browseraol.html
// for detailed lists of userAgent strings.
//
// Note: you don't want your Nav4 or IE4 code to "turn off" or
// stop working when Nav5 and IE5 (or later) are released, so
// in conditional code forks, use is.nav4up ("Nav4 or greater")
// and is.ie4up ("IE4 or greater") instead of is.nav4 or is.ie4
// to check version in code which you want to work on future
// versions.


function Is ()
{   // convert all characters to lowercase to simplify testing
    var agt=navigator.userAgent.toLowerCase();

    // *** BROWSER VERSION ***
    // Note: On IE5, these return 4, so use is.ie5up to detect IE5.

    this.major = parseInt(navigator.appVersion);
    this.minor = parseFloat(navigator.appVersion);

    // Note: Opera and WebTV spoof Navigator.  We do strict client detection.
    // If you want to allow spoofing, take out the tests for opera and webtv.
    this.nav  = ((agt.indexOf('mozilla')!=-1) && (agt.indexOf('spoofer')==-1)
                && (agt.indexOf('compatible') == -1) && (agt.indexOf('opera')==-1)
                && (agt.indexOf('webtv')==-1) && (agt.indexOf('hotjava')==-1));
    this.nav2 = (this.nav && (this.major == 2));
    this.nav3 = (this.nav && (this.major == 3));
    this.nav4 = (this.nav && (this.major == 4));
    this.nav4up = (this.nav && (this.major >= 4));
    this.navonly      = (this.nav && ((agt.indexOf(";nav") != -1) ||
                          (agt.indexOf("; nav") != -1)) );
    this.nav6 = (this.nav && (this.major == 5));
    this.nav6up = (this.nav && (this.major >= 5));
    this.gecko = (agt.indexOf('gecko') != -1);


    this.ie     = ((agt.indexOf("msie") != -1) && (agt.indexOf("opera") == -1));
    this.ie3    = (this.ie && (this.major < 4));
    this.ie4    = (this.ie && (this.major == 4) && (agt.indexOf("msie 4")!=-1) );
    this.ie4up  = (this.ie  && (this.major >= 4));
    this.ie5    = (this.ie && (this.major == 4) && (agt.indexOf("msie 5.0")!=-1) );
    this.ie5_5  = (this.ie && (this.major == 4) && (agt.indexOf("msie 5.5") !=-1));
    this.ie5up  = (this.ie  && !this.ie3 && !this.ie4);
    this.ie5_5up =(this.ie && !this.ie3 && !this.ie4 && !this.ie5);
    this.ie6    = (this.ie && (this.major == 4) && (agt.indexOf("msie 6.")!=-1) );
    this.ie6up  = (this.ie  && !this.ie3 && !this.ie4 && !this.ie5 && !this.ie5_5);

    // KNOWN BUG: On AOL4, returns false if IE3 is embedded browser
    // or if this is the first browser window opened.  Thus the
    // variables is.aol, is.aol3, and is.aol4 aren't 100% reliable.
    this.aol   = (agt.indexOf("aol") != -1);
    this.aol3  = (this.aol && this.ie3);
    this.aol4  = (this.aol && this.ie4);
    this.aol5  = (agt.indexOf("aol 5") != -1);
    this.aol6  = (agt.indexOf("aol 6") != -1);

    this.opera = (agt.indexOf("opera") != -1);
    this.opera2 = (agt.indexOf("opera 2") != -1 || agt.indexOf("opera/2") != -1);
    this.opera3 = (agt.indexOf("opera 3") != -1 || agt.indexOf("opera/3") != -1);
    this.opera4 = (agt.indexOf("opera 4") != -1 || agt.indexOf("opera/4") != -1);
    this.opera5 = (agt.indexOf("opera 5") != -1 || agt.indexOf("opera/5") != -1);
    this.opera5up = (this.opera && !this.opera2 && !this.opera3 && !this.opera4);

    this.webtv = (agt.indexOf("webtv") != -1); 

    this.TVNavigator = ((agt.indexOf("navio") != -1) || (agt.indexOf("navio_aoltv") != -1)); 
    this.AOLTV = this.TVNavigator;

    this.hotjava = (agt.indexOf("hotjava") != -1);
    this.hotjava3 = (this.hotjava && (this.major == 3));
    this.hotjava3up = (this.hotjava && (this.major >= 3));

    // *** JAVASCRIPT VERSION CHECK ***
    if (this.nav2 || this.ie3) this.js = 1.0;
    else if (this.nav3) this.js = 1.1;
    else if (this.opera5up) this.js = 1.3;
    else if (this.opera) this.js = 1.1;
    else if ((this.nav4 && (this.minor <= 4.05)) || this.ie4) this.js = 1.2;
    else if ((this.nav4 && (this.minor > 4.05)) || this.ie5) this.js = 1.3;
    else if (this.hotjava3up) this.js = 1.4;
    else if (this.nav6 || this.gecko) this.js = 1.5;
    // NOTE: In the future, update this code when newer versions of JS
    // are released. For now, we try to provide some upward compatibility
    // so that future versions of Nav and IE will show they are at
    // *least* JS 1.x capable. Always check for JS version compatibility
    // with > or >=.
    else if (this.nav6up) this.js = 1.5;
    // note ie5up on mac is 1.4
    else if (this.ie5up) this.js = 1.3

    // HACK: no idea for other browsers; always check for JS version with > or >=
    else this.js = 0.0;

    // *** PLATFORM ***
    this.win   = ( (agt.indexOf("win")!=-1) || (agt.indexOf("16bit")!=-1) );
    // NOTE: On Opera 3.0, the userAgent string includes "Windows 95/NT4" on all
    //        Win32, so you can't distinguish between Win95 and WinNT.
    this.win95 = ((agt.indexOf("win95")!=-1) || (agt.indexOf("windows 95")!=-1));

    // is this a 16 bit compiled version?
    this.win16 = ((agt.indexOf("win16")!=-1) || 
               (agt.indexOf("16bit")!=-1) || (agt.indexOf("windows 3.1")!=-1) || 
               (agt.indexOf("windows 16-bit")!=-1) );  

    this.win31 = ((agt.indexOf("windows 3.1")!=-1) || (agt.indexOf("win16")!=-1) ||
                    (agt.indexOf("windows 16-bit")!=-1));

    // NOTE: Reliable detection of Win98 may not be possible. It appears that:
    //       - On Nav 4.x and before you'll get plain "Windows" in userAgent.
    //       - On Mercury client, the 32-bit version will return "Win98", but
    //         the 16-bit version running on Win98 will still return "Win95".
    this.win98 = ((agt.indexOf("win98")!=-1) || (agt.indexOf("windows 98")!=-1));
    this.winnt = ((agt.indexOf("winnt")!=-1) || (agt.indexOf("windows nt")!=-1));
    this.win32 = (this.win95 || this.winnt || this.win98 || 
                    ((this.major >= 4) && (navigator.platform == "Win32")) ||
                    (agt.indexOf("win32")!=-1) || (agt.indexOf("32bit")!=-1));

    this.winme = ((agt.indexOf("win 9x 4.90")!=-1));
    this.win2k = ((agt.indexOf("windows nt 5.0")!=-1));

    this.os2   = ((agt.indexOf("os/2")!=-1) || 
                    (navigator.appVersion.indexOf("OS/2")!=-1) ||   
                    (agt.indexOf("ibm-webexplorer")!=-1));

    this.mac    = (agt.indexOf("mac")!=-1);
    // hack ie5 js version for mac
    if (this.mac && this.ie5up) this.js = 1.4;
    this.mac68k = (this.mac && ((agt.indexOf("68k")!=-1) || 
                               (agt.indexOf("68000")!=-1)));
    this.macppc = (this.mac && ((agt.indexOf("ppc")!=-1) || 
                                (agt.indexOf("powerpc")!=-1)));

    this.sun   = (agt.indexOf("sunos")!=-1);
    this.sun4  = (agt.indexOf("sunos 4")!=-1);
    this.sun5  = (agt.indexOf("sunos 5")!=-1);
    this.suni86= (this.sun && (agt.indexOf("i86")!=-1));
    this.irix  = (agt.indexOf("irix") !=-1);    // SGI
    this.irix5 = (agt.indexOf("irix 5") !=-1);
    this.irix6 = ((agt.indexOf("irix 6") !=-1) || (agt.indexOf("irix6") !=-1));
    this.hpux  = (agt.indexOf("hp-ux")!=-1);
    this.hpux9 = (this.hpux && (agt.indexOf("09.")!=-1));
    this.hpux10= (this.hpux && (agt.indexOf("10.")!=-1));
    this.aix   = (agt.indexOf("aix") !=-1);      // IBM
    this.aix1  = (agt.indexOf("aix 1") !=-1);    
    this.aix2  = (agt.indexOf("aix 2") !=-1);    
    this.aix3  = (agt.indexOf("aix 3") !=-1);    
    this.aix4  = (agt.indexOf("aix 4") !=-1);    
    this.linux = (agt.indexOf("inux")!=-1);
    this.sco   = (agt.indexOf("sco")!=-1) || (agt.indexOf("unix_sv")!=-1);
    this.unixware = (agt.indexOf("unix_system_v")!=-1); 
    this.mpras    = (agt.indexOf("ncr")!=-1); 
    this.reliant  = (agt.indexOf("reliantunix")!=-1);
    this.dec   = ((agt.indexOf("dec")!=-1) || (agt.indexOf("osf1")!=-1) || 
                  (agt.indexOf("dec_alpha")!=-1) || (agt.indexOf("alphaserver")!=-1) || 
                  (agt.indexOf("ultrix")!=-1) || (agt.indexOf("alphastation")!=-1)); 
    this.sinix = (agt.indexOf("sinix")!=-1);
    this.freebsd = (agt.indexOf("freebsd")!=-1);
    this.bsd = (agt.indexOf("bsd")!=-1);
    this.unix  = ((agt.indexOf("x11")!=-1) || this.sun || this.irix || this.hpux || 
                 this.sco ||this.unixware || this.mpras || this.reliant || 
                 this.dec || this.sinix || this.aix || this.linux || this.bsd || this.freebsd);

    this.vms   = ((agt.indexOf("vax")!=-1) || (agt.indexOf("openvms")!=-1));
}

var is;
var isIE3Mac = false;
// this section is designed specifically for IE3 for the Mac

if ((navigator.appVersion.indexOf("Mac")!=-1) && (navigator.userAgent.indexOf("MSIE")!=-1) && 
(parseInt(navigator.appVersion)==3))
       isIE3Mac = true;
else   is = new Is(); 

//--> end hide JavaScript

Here are the results of running that JavaScript code on the browser you are using. The below text has been dynamically generated after checking your browser vendor, version, and operating system from JavaScript.
Basic Data

Version Number

Browser Version

JavaScript Version

OS