an easy plugin to check the browser version and you can also use callback to block these kind of old fashion browser or do anything else

jq.dectectBrowserVersion.js

/*
* author: blackbing@gamil.com
* version: 0.1
* date: 2011/01/24
* description: I am confused by browser version detection. What I need is blocking the browsers which are ie6/ie7/ff3 , however, I can't easily detect browser version. Cause I got the version which is like that "6.0.2900.5512.xpsp_sp3_gdr.100427-1636".
so I write an easy plugin to check the browser version and you can also use callback to block these kind of old fashion browser or do anything else.

For example:
$.dectectBrowserVersion({
    filter: {
        webkit: '535'
    },
    callback: function(){
        alert('do you live in stone age?');
    }
});
*/
(function($) {

    $.dectectBrowserVersion = function(opts) {
        var filter = opts && opts.filter ? opts.filter : {};
        var callback = opts && opts.callback ? opts.callback : null;
        //ready to set stubborn and ignore the setting 
        var allcookies = document.cookie;
        var pos = allcookies.indexOf("stubborn=");
        if (pos != -1) {
            var st = pos + 9;
            var end = allcookies.indexOf(";", st);
            if (end == -1) {
                end = allcookies.length;
            }
            var value = allcookies.substring(st, end);
            value = decodeURIComponent(value);
            if (value == '1') {
                return false;
            }
        }
        //these above are ignore the detection
        //filtered browsers and lower version 
        var filterBrowsers = {
            'msie': '7',
            'mozilla': '1.9.1'
        };
        filterBrowsers = $.extend(filterBrowsers, filter);
        var default_callback = function() {
            alert('you are using old fashion browser!!');
        };
        callback = callback || default_callback;
        var formatVersion = function(version) {
            //to string
            version += '';
            //get version number
            var versionReg = /[\d]+[\.\d]+/ig;
            var res = versionReg.exec(version);
            if (res && res.length) {
                version = res[0];
            }
            var sp = version.split('.');
            var re = sp[0] + '.';
            for (var i = 1; i < sp.length; i++) {
                re += sp[i];
            }
            return +re;
        };
        $.each($.browser, function(k, w) {
            var filterBrowser = formatVersion(filterBrowsers[k]);
            if ($.browser[k] && filterBrowser) {
                var v = formatVersion($.browser.version);
                if (v <= filterBrowser && callback) {
                    //callback and do something
                    callback();
                }
            }
        });

    };
})(jQuery);