代码来自红宝书,真的是贼完整和详细

包括检测呈现引擎、平台、Windows 操作系统、移动设备 和游戏系统

    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"];
                }
            }
        }
        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
        };
    }();