js浏览器判断函数

function userBrowser(){
    var browserName=navigator.userAgent.toLowerCase();
    if(/msie/i.test(browserName) && !/opera/.test(browserName)){
        alert("IE");
        return ;
    }else if(/firefox/i.test(browserName)){
        alert("Firefox");
        return ;
    }else if(/chrome/i.test(browserName) && /webkit/i.test(browserName) && /mozilla/i.test(browserName)){
        alert("Chrome");
        return ;
    }else if(/opera/i.test(browserName)){
        alert("Opera");
        return ;
    }else if(/webkit/i.test(browserName) &&!(/chrome/i.test(browserName) && /webkit/i.test(browserName) && /mozilla/i.test(browserName))){
        alert("Safari");
        return ;
    }else{
        alert("unKnow");
    }
}