怎么样通过浏览器检测JS代码？

var BrowserMatch = {
 init: function () {
  this.browser = this.getBrowser().browser || "An Unknown Browser";
  this.version = this.getBrowser().version || "An Unknown Version";
  this.OS = this.getOS() || "An Unknown OS";
 },
 getOS:function(){
  if(navigator.platform.indexOf("Win")!= -1) return "Windows";
  if(navigator.platform.indexOf("Mac")!= -1) return "Mac";
  if(navigator.platform.indexOf("Linux")!= -1) return "Linux";
  if(navigator.userAgent.indexOf("iPhone")!= -1) return "iPhone/iPod";
 },
 getBrowser:function () {
  var rMsie = /(msie\s|trident\/7)([\w\.]+)/;
  var rTrident = /(trident)\/([\w.]+)/;
  var rFirefox = /(firefox)\/([\w.]+)/; 
  var rOpera = /(opera).+version\/([\w.]+)/;
  var rNewOpera = /(opr)\/(.+)/;
  var rChrome = /(chrome)\/([\w.]+)/;
  var rSafari = /version\/([\w.]+).*(safari)/;
  var ua = navigator.userAgent.toLowerCase();
  var matchBS,matchBS2;
  matchBS = rMsie.exec(ua);
  if (matchBS != null) {
   matchBS2 = rTrident.exec(ua);
   if (matchBS2 != null){
    switch (matchBS2[2]){
     case "4.0": return { browser : "IE", version : "8" };break;
     case "5.0": return { browser : "IE", version : "9" };break;
     case "6.0": return { browser : "IE", version : "10" };break;
     case "7.0": return { browser : "IE", version : "11" };break;
     default:return { browser : "IE", version : "Undefined" };
    }
   }else{
    return {browser : "IE", version : matchBS[2] || "0" };
   }
  }
  matchBS = rFirefox.exec(ua); 
  if ((matchBS != null)&&(!(window.attachEvent))&&(!(window.chrome))&&(!(window.opera))) { 
   return { browser : matchBS[1] || "", version : matchBS[2] || "0" };
  }
  matchBS = rOpera.exec(ua);     
  if ((matchBS != null)&&(!(window.attachEvent))) {   
   return { browser : matchBS[1] || "", version : matchBS[2] || "0" };
  }
  matchBS = rChrome.exec(ua); 
  if ((matchBS != null)&&(!!(window.chrome))&&(!(window.attachEvent))) {
   matchBS2 = rNewOpera.exec(ua);    
   if(matchBS2 == null){
    return { browser : matchBS[1] || "", version : matchBS[2] || "0" };
   }else{
    return { browser : "Opera", version : matchBS2[2] || "0" };
   } 
  }
  matchBS = rSafari.exec(ua);     
  if ((matchBS != null)&&(!(window.attachEvent))&&(!(window.chrome))&&(!(window.opera))) {  
   return { browser : matchBS[2] || "", version : matchBS[1] || "0" };
  }      
 }
}; 
BrowserMatch.init();