使用特定时区的Javascript时钟

Question

我有以下javascript函数可以正常工作，但是它应该只显示CST（GMT-5）中的时间，而不管观看者的时区是什么。如何修改它呢？

function updateClock () {
    var currentTime = new Date();
    var currentHours = currentTime.getHours();
    var currentMinutes = currentTime.getMinutes();
    var currentSeconds = currentTime.getSeconds();

    currentMinutes = (currentMinutes < 10 ? "0" : "") + currentMinutes;
    currentSeconds = (currentSeconds < 10 ? "0" : "") + currentSeconds;

    var timeOfDay = (currentHours < 12) ? "AM" : "PM";
    currentHours = (currentHours > 12) ? currentHours-12 : currentHours;
    currentHours = (currentHours == 0) ? 12 : currentHours;

    var currentTimeString = currentHours + ":" + currentMinutes + ":" + currentSeconds + " " + timeOfDay;

    document.getElementById("clock").firstChild.nodeValue = currentTimeString;
}