用户代理检测

var client = function(){
 //呈现引擎
 var engine = {
 ie: 0,
 gecko: 0,
 webkit: 0,
 khtml: 0,
 opera: 0,

 //完整的版本号
 ver: null
 };
 //浏览器
 var browser = {

 //主要浏览器
 ie: 0,
 firefox: 0,
 safari: 0,
 konq: 0,
 opera: 0,
 chrome: 0,

 //具体的版本号
 ver: null
 };
 //平台、设备和操作系统
 var system = {
 win: false,
 mac: false,
 x11: false,

 //移动设备
 iphone: false,
 ipod: false,
 ipad: false,
 ios: false,
 android: false,
 nokiaN: false,
 winMobile: false,

 //游戏系统
 wii: false,
 ps: false
 };

 //检测呈现引擎和浏览器
 var ua = navigator.userAgent;
 if (window.opera){
 engine.ver = browser.ver = window.opera.version();
 engine.opera = browser.opera = parseFloat(engine.ver);
 } else if (/AppleWebKit\/(\S+)/.test(ua)){
 engine.ver = RegExp["$1"];
 engine.webkit = parseFloat(engine.ver);

 //确定是 Chrome 还是 Safari
 if (/Chrome\/(\S+)/.test(ua)){
 browser.ver = RegExp["$1"];
 browser.chrome = parseFloat(browser.ver);
 } else if (/Version\/(\S+)/.test(ua)){
 browser.ver = RegExp["$1"];
 browser.safari = parseFloat(browser.ver);
 } else {
 //近似地确定版本号
 var safariVersion = 1;
 if (engine.webkit < 100){
 safariVersion = 1;
 } else if (engine.webkit < 312){
 safariVersion = 1.2;
 } else if (engine.webkit < 412){
 safariVersion = 1.3;
 } else {
 safariVersion = 2;
 }

 browser.safari = browser.ver = safariVersion;
 } 
} else if (/KHTML\/(\S+)/.test(ua) || /Konqueror\/([^;]+)/.test(ua)){
 engine.ver = browser.ver = RegExp["$1"];
 engine.khtml = browser.konq = parseFloat(engine.ver);
 } else if (/rv:([^\)]+)\) Gecko\/\d{8}/.test(ua)){
 engine.ver = RegExp["$1"];
 engine.gecko = parseFloat(engine.ver);

 //确定是不是 Firefox
 if (/Firefox\/(\S+)/.test(ua)){
 browser.ver = RegExp["$1"];
 browser.firefox = parseFloat(browser.ver);
 }
 } else if (/MSIE ([^;]+)/.test(ua)){
 engine.ver = browser.ver = RegExp["$1"];
 engine.ie = browser.ie = parseFloat(engine.ver);
 }
 //检测浏览器
 browser.ie = engine.ie;
 browser.opera = engine.opera;
 //检测平台
 var p = navigator.platform;
 system.win = p.indexOf("Win") == 0;
 system.mac = p.indexOf("Mac") == 0;
 system.x11 = (p == "X11") || (p.indexOf("Linux") == 0);
 //检测 Windows 操作系统
 if (system.win){
 if (/Win(?:dows )?([^do]{2})\s?(\d+\.\d+)?/.test(ua)){
 if (RegExp["$1"] == "NT"){
 switch(RegExp["$2"]){
 case "5.0":
 system.win = "2000";
 break;
 case "5.1":
 system.win = "XP";
 break;
 case "6.0":
 system.win = "Vista";
 break;
 case "6.1":
 system.win = "7";
 break;
 default:
 system.win = "NT";
 break;
 }
 } else if (RegExp["$1"] == "9x"){
 system.win = "ME";
 } else {
 system.win = RegExp["$1"];
 }
 }
 }
 //移动设备
system.iphone = ua.indexOf("iPhone") > -1;
 system.ipod = ua.indexOf("iPod") > -1;
 system.ipad = ua.indexOf("iPad") > -1;
 system.nokiaN = ua.indexOf("NokiaN") > -1;
 //windows mobile
 if (system.win == "CE"){
 system.winMobile = system.win;
 } else if (system.win == "Ph"){
 if(/Windows Phone OS (\d+.\d+)/.test(ua)){;
 system.win = "Phone";
 system.winMobile = parseFloat(RegExp["$1"]);
 }
 }

 //检测 iOS 版本
 if (system.mac && ua.indexOf("Mobile") > -1){
 if (/CPU (?:iPhone )?OS (\d+_\d+)/.test(ua)){
 system.ios = parseFloat(RegExp.$1.replace("_", "."));
 } else {
 system.ios = 2; //不能真正检测出来，所以只能猜测
 }
 }
 //检测 Android 版本
 if (/Android (\d+\.\d+)/.test(ua)){
 system.android = parseFloat(RegExp.$1);
 }
 //游戏系统
 system.wii = ua.indexOf("Wii") > -1;
 system.ps = /playstation/i.test(ua);
 //返回这些对象
 return {
 engine: engine,
 browser: browser,
 system: system
 };
}();