通过HTTP头部的user-agent进行浏览器兼容性检测

以下检测的顺序最好不要变动。

user-agent如

Mozilla/5.0 (Platform; Encryption; OS-or-CPU; Language) AppleWebKit/AppleWebKitVersion (KHTML, like Gecko) Safari/SafariVersion

Mozilla/MozillaVersion (Platform; Encryption; OS-or-CPU; Language; PrereleaseVersion)Gecko/GeckoVersion ApplicationProduct/ApplicationProductVersion

eg：Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:0.9.4) Gecko/20011128 Netscape6/6.2.1

var client = function(){
var engine = {
//rendering engines
ie: 0,
gecko: 0,
webkit: 0,
khtml: 0,
opera: 0,
//specific version
ver: null
};

var browser = {

//browsers

ie: 0,

firefox: 0,

safari: 0,

konq: 0,

opera: 0,

chrome: 0,

safari: 0,

//specific version

ver: null

};

var system = {

win: false,

mac: false,

x11: false

};

//detection of rendering engines/platforms/devices here

return {

engine: engine,

browser: browser,

system: system

};

}();//detect rendering engines/browsers

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);

//figure out if it’s Chrome or 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 {

//approximate version

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);

//determine if it’s 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);

}