浏览器JavaScript库提供了此功能。

if (bowser.msie && bowser.version <= 6) {
  alert('Hello China');
}

它似乎保养得很好。

看看navigator。userAgent - Firefox/xxx.xxx. xxx。XXX是在结尾指定的。

jQuery可以很好地处理这个问题(jQuery.browser)

var ua = $.browser;
if ( ua.mozilla && ua.version.slice(0,3) == "1.9" ) {
    alert( "Do stuff for firefox 3" );
}

编辑:正如Joshua在他的评论下面所写的，jQuery。jQuery自1.9版起不再支持browser属性(详情请参阅jQuery 1.9发布说明)。 jQuery开发团队建议使用更完整的方法，例如使用Modernizr库调整UI。

var nVer = navigator.appVersion;
var nAgt = navigator.userAgent;
var browserName  = navigator.appName;
var fullVersion  = ''+parseFloat(navigator.appVersion);
var majorVersion = parseInt(navigator.appVersion,10);
var nameOffset,verOffset,ix;

// In Opera, the true version is after "Opera" or after "Version"

if ((verOffset=nAgt.indexOf("Opera"))!=-1) {
 browserName = "Opera";
 fullVersion = nAgt.substring(verOffset+6);
 if ((verOffset=nAgt.indexOf("Version"))!=-1)
   fullVersion = nAgt.substring(verOffset+8);
}
// In MSIE, the true version is after "MSIE" in userAgent

else if ((verOffset=nAgt.indexOf("MSIE"))!=-1) {
 browserName = "Microsoft Internet Explorer";
 fullVersion = nAgt.substring(verOffset+5);
}
// In Chrome, the true version is after "Chrome"

else if ((verOffset=nAgt.indexOf("Chrome"))!=-1) {
 browserName = "Chrome";
 fullVersion = nAgt.substring(verOffset+7);
}
// In Safari, the true version is after "Safari" or after "Version"

else if ((verOffset=nAgt.indexOf("Safari"))!=-1) {
 browserName = "Safari";
 fullVersion = nAgt.substring(verOffset+7);
 if ((verOffset=nAgt.indexOf("Version"))!=-1)
   fullVersion = nAgt.substring(verOffset+8);
}
// In Firefox, the true version is after "Firefox"

else if ((verOffset=nAgt.indexOf("Firefox"))!=-1) {
 browserName = "Firefox";
 fullVersion = nAgt.substring(verOffset+8);
}
// In most other browsers, "name/version" is at the end of userAgent

else if ( (nameOffset=nAgt.lastIndexOf(' ')+1) <
          (verOffset=nAgt.lastIndexOf('/')) )
{
 browserName = nAgt.substring(nameOffset,verOffset);
 fullVersion = nAgt.substring(verOffset+1);
 if (browserName.toLowerCase()==browserName.toUpperCase()) {
  browserName = navigator.appName;
 }
}

// trim the fullVersion string at semicolon/space if present

if ((ix=fullVersion.indexOf(";"))!=-1)
   fullVersion=fullVersion.substring(0,ix);
if ((ix=fullVersion.indexOf(" "))!=-1)
   fullVersion=fullVersion.substring(0,ix);

majorVersion = parseInt(''+fullVersion,10);
if (isNaN(majorVersion)) {
 fullVersion  = ''+parseFloat(navigator.appVersion);
 majorVersion = parseInt(navigator.appVersion,10);
}

document.write(''
 +'Browser name  = '+browserName+'<br>'
 +'Full version  = '+fullVersion+'<br>'
 +'Major version = '+majorVersion+'<br>'
 +'navigator.appName = '+navigator.appName+'<br>'
 +'navigator.userAgent = '+navigator.userAgent+'<br>'
)

看这里的演示..http://jsfiddle.net/hw4jM/3/

我写这个是为了满足我的需要。

它可以获取信息，比如是否是移动设备或是否有视网膜显示器

试一试

var nav = {
        isMobile:function(){
            return (navigator.userAgent.match(/iPhone|iPad|iPod|Android|BlackBerry|Opera Mini|IEMobile/i) != null);
        },
        isDesktop:function(){
            return (navigator.userAgent.match(/iPhone|iPad|iPod|Android|BlackBerry|Opera Mini|IEMobile/i) == null);
        },
        isAndroid: function() {
            return navigator.userAgent.match(/Android/i);
        },
        isBlackBerry: function() {
            return navigator.userAgent.match(/BlackBerry/i);
        },
        isIOS: function() {
            return navigator.userAgent.match(/iPhone|iPad|iPod/i);
        },
        isOpera: function() {
            return navigator.userAgent.match(/Opera Mini/i);
        },
        isWindows: function() {
            return navigator.userAgent.match(/IEMobile/i);
        },
        isRetina:function(){
            return window.devicePixelRatio && window.devicePixelRatio > 1;
        },
        isIPad:function(){
            isIPad = (/ipad/gi).test(navigator.platform);
            return isIPad;
        },
        isLandscape:function(){
            if(window.innerHeight < window.innerWidth){
                return true;
            }
            return false;
        },
        getIOSVersion:function(){
            if(this.isIOS()){
                var OSVersion = navigator.appVersion.match(/OS (\d+_\d+)/i);
                OSVersion = OSVersion[1] ? +OSVersion[1].replace('_', '.') : 0;
                return OSVersion;
            }
            else
                return false;
        },
        isStandAlone:function(){
            if(_.is(navigator.standalone))
                return navigator.standalone;
            return false;
        },
        isChrome:function(){
            var isChrome = (/Chrome/gi).test(navigator.appVersion);
            var isSafari = (/Safari/gi).test(navigator.appVersion)
            return isChrome && isSafari;
        },
        isSafari:function(){
            var isSafari = (/Safari/gi).test(navigator.appVersion)
            var isChrome = (/Chrome/gi).test(navigator.appVersion)
            return !isChrome && isSafari;
        }
}

浏览器JavaScript库提供了此功能。

if (bowser.msie && bowser.version <= 6) {
  alert('Hello China');
}

它似乎保养得很好。