This is the other solution :

navigator.sayswho= (function(){
var ua= navigator.userAgent;
var tem; 
var M= ua.match(/(opera|chrome|safari|firefox|msie|trident(?=\/))\/?\s*(\d+)/i) || [];
if(/trident/i.test(M[1])){
    tem=  /\brv[ :]+(\d+)/g.exec(ua) || [];
    return 'IE '+(tem[1] || '');
}
if(M[1]=== 'Chrome'){
    tem= ua.match(/\b(OPR|Edge)\/(\d+)/);
    if(tem!= null) return tem.slice(1).join(' ').replace('OPR', 'Opera');
}
M= M[2]? [M[1], M[2]]: [navigator.appName, navigator.appVersion, '-?'];
if((tem= ua.match(/version\/(\d+)/i))!= null) M.splice(1, 1, tem[1]);
return M.join(' ');})();

alert(navigator.sayswho);

You can use Browser detect which gives you information regarding your browser and versions

alert(BrowserDetect.browser);
alert(BrowserDetect.version);

Another option is using navigator.appVersion but it was deprecated lately

alert(navigator.appVersion);

Why not just do that serverside prior to even delivering the page ? The HTTP request often includes a user agent header (which is the browser brand/version/etc).

The exact implementation depends on what exactly your "site" is and on what type of webserver it runs.

If it's a PHP application then you could use $_SERVER['HTTP_USER_AGENT'].

If the site uses plain old static .html files and runs on Apache httpd, then you could use RewriteCond %{HTTP_USER_AGENT} ...something...

and so on.