js识别不同浏览器基于userAgent做判断

//检测浏览器
var client = function(){
var engine = {
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 ua = navigator.userAgent;
//浏览器检测有顺序
if(window.opera){//opera伪装，所以优先检测
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);
}
return {
engine:engine,
browser: browser
};
}();


//调用

if (client.engine.webkit) { //if it's 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 
} 
}