js 判断IE浏览器，包含IE6/7/8/9

//判断IE6-9的版本，num可取值为6/7/8/9
//若不给参数num，仅判断浏览器是否为IE，不判断版本

var isIE = function (num)
{
    if(arguments.length == 0){
        if (!!window.ActiveXObject || "ActiveXObject" in window)
      {
      return true;
    }
    else
      {
      return false;
    }
    }
    var browser = navigator.appName;
    var b_version = navigator.appVersion;
    var version = b_version.split(";");
    var trim_Version = version[1].replace(/[ ]/g,"");
    var version_num = 0;
    if(browser=="Microsoft Internet Explorer" && trim_Version=="MSIE6.0")
    {
        version_num = 6;
    }
    else if(browser=="Microsoft Internet Explorer" && trim_Version=="MSIE7.0")
    {
        version_num = 7;
    }
    else if(browser == "Microsoft Internet Explorer" && trim_Version=="MSIE8.0")
    {
        version_num = 8;
    }
    else if(browser == "Microsoft Internet Explorer" && trim_Version=="MSIE9.0")
    {
        version_num= 9;
    }
    return version_num==num?true:false;
}