function getIEVersion()
{
    var rv = -1; // Return value assumes failure.
    if(navigator.appName == 'Microsoft Internet Explorer') {
        var ua = navigator.userAgent;
        var re = new RegExp("MSIE ([0-9]{1,}[\.0-9]{0,})");
if(re.exec(ua) != null)
    rv = parseFloat(RegExp.$1);
}
return rv;
}

function checkVersion() {
    var msg = "You're not using Internet Explorer.";
    var ver = getIEVersion();

    if(ver > -1) {
        alert(ver);
        if(ver >= 9.0)//这里写明要检测的版本
            msg = "You're using a recent copy of Internet Explorer."
        else
            msg = "You should upgrade your copy of Internet Explorer.";
    }
    alert(msg);
}