js浏览器检测(包括引擎、浏览器、运行环境、pc和移动端检测)

该函数用于正确识别浏览器相关内容，代码来自于《javaScript高级程序设计》

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
                };
            }();

这个检测可以说是很全了。

不过，

用户代理检测是客户端检测的最后一个选择。

只要可能，都应该优先采用能力检测和怪癖检测。