Javascript识别各种浏览器、渲染引擎、系统平台(操作系统|移动设备|游戏系统)

有时候我们需要检测客户端使用的浏览器是什么来做一些差异的操作,下面是摘自《Javascript高级程序设计》检测代码：

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

        ver: null
    };
    var browser = { //浏览器
        ie: 0,
        firefox: 0,
        safari: 0,
        konq: 0,
        opera: 0,
        chrome: 0,

        ver: null
    };
    var system = { //系统平台
        win: false,
        mac: false,
        x11: false,

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

        //游戏系统
        wii: false,
        ps: false
    };

    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);

        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);

        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);
    }

    var p = navigator.platform;
    system.win = p.indexOf("Win") == 0;
    system.mac = p.indexOf("Mac") == 0;
    system.x11 = (p == "X11") || (p.indexOf("Linux") == 0);

    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;
    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"]);
        }
    }
    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; //近似
        }
    }
    if(/Android (\d+\.\d+)/.test(ua)) {
        system.android = parseFloat(RegExp["$1"]);
    }
    system.wii = ua.indexOf("Wii") > -1;
    system.ps = /playstation/i.test(ua);

    return {
        engine: engine,
        browser: browser,
        system: system
    };
})();

使用例子：

if(client.engine.ie) {
    //针对IE的代码
} else if(client.engine.gecko > 1.5) {
    if(client.engine.gecko == "1.8.1") {
        //针对这个版本执行某些操作
    }
}

if(client.engine.webkit) {
    if(client.browser.chrome) {
        //执行针对Chrome的代码
    } else if(client.browser.safari) {
        //执行针对Safari的代码
    }
} else if(client.engine.gecko) {
    if(client.browser.firefox) {
        //执行针对Firefox的代码
    } else {
        //执行针对其他Gecko浏览器的代码
    }
}

if(client.engine.webkit) {
    if(client.system.ios) {
        //iOS手机的代码
    } else if(client.system.android) {
        //Android手机的代码
    }
}
...