Javascript date 在 ie8 中显示 nan

下面的代码在IE8以外的任何浏览器中都能很好地工作。我正在从服务器中获取时间并尝试在IE8中显示日期字符串和服务器小时。我得到的是字符串，serverHour，是未定义的未定义未定义未定义，对于小时，testHours，我得到nan。我尝试使用moment.js来显示日期，但我得到相同的结果。任何指导将不胜感激。我尝试了几种不同的方式重新格式化日期字符串，但我找不到有效的组合。我一定错过了一些非常基本的东西。

var xmlHttp;
var offset = 0;
var today = new Date();
/* 
return the standard time timezone offset regardless of whether the current time is on standard or daylight saving time. 
http://www.webdeveloper.com/forum/showthread.php?228309-Getting-server-date-time-with-no-server-side-script
*/
Date.prototype.stdTimezoneOffset = function () {
    var jan = new Date(this.getFullYear(), 0, 1);
    var jul = new Date(this.getFullYear(), 6, 1);
    return Math.max(jan.getTimezoneOffset(), jul.getTimezoneOffset());
}
/*
Determine if the current time is on daylight saving time or not. We simply compare the current  timezone offset with the standard one. 
If they are equal then the current time is standard time. If they are not     then the current   time is daylight saving time. This second 
method will return true when the current time is daylight saving time and false when it is    standard time.
http://www.webdeveloper.com/forum/showthread.php?228309-Getting-server-date-time-with-no-server-       side-script
*/
Date.prototype.dst = function () {
    return this.getTimezoneOffset() < this.stdTimezoneOffset();
}
// Convert GMT server time to Pacific time and return date.
function getServerTime(serverDateMs,offset) {
    var date = new Date(serverDateMs + offset * 3600 * 1000);
    return date;
}
// Function to get server time in GMT
function srvTime() {
// Create an XML object to collect information from server
try {
    //FF, Opera, Safari, Chrome
    xmlHttp = new XMLHttpRequest();
}
catch (err1) {
    //IE
    try {
        xmlHttp = new ActiveXObject('Msxml2.XMLHTTP');
    }
    catch (err2) {
        try {
            xmlHttp = new ActiveXObject('Microsoft.XMLHTTP');
        }
        catch (err3) {
            //AJAX not supported, use CPU time.
            alert("AJAX not supported");
        }
    }
}
// Request information from the server using XML object
xmlHttp.open('POST', window.location.href, false);
xmlHttp.send();
return xmlHttp.getResponseHeader("Date");
}
// Set offset if daylight savings time or standard time
if (today.dst() == true) { offset = -7; }
else { offset = -8; }
var x = srvTime();
//i have: Fri, 02 Jan 2015 22:54:05 GMT
// modify the string to remove comma and GMT
var dateString = x.replace(",", "").replace("GMT", "");
var a = dateString.split(" ");
//I want: Nov 06 2012 23:29:33 +0000
// reorganize to match above format
var newDatString = a[2] + " " + a[1] + " " + a[3] + " " + a[4];
// create the date object
var serverT = new Date(newDatString);
// get date/time in milliseconds
var serverDateMs = serverT.getTime();
// convert GMT time to pacific time
var serverDatePacific = getServerTime(serverDateMs, offset);
// create date object from pacific time
var serverHour = new Date(serverDatePacific);
// get hours from pacific time date object
var testHour = serverHour.getHours();