浏览器识别（包括呈现引擎，浏览器版本，操作系统，移动设备）

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 = {    //主要的浏览器    ie: 0,     firefox: 0,     safari: 0,     konq: 0,     opera: 0,    chrome: 0,    //具体的版本号    ver: null };//操作系统var system = {    win: 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 {    //大概地确定版本号        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 { 12            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 mobileif (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设备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，只能猜测        }}//检测Android设备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}; }();

一般应优先考虑能力检测，其次是怪癖检测，最后才是浏览器识别（因为基于用户代理检测，对用户代理字符串有很强的依赖性，而用户代理字符串由于其历史原因具有欺骗性）

摘除自JavaScript高级程序设计第3版