在IE浏览器显示NaN

<script type="text/javascript">
    var time_now_server, time_now_client, time_end, time_server_client, timerID;
    var a = '@ViewBag.StartTime';//开始的时间  注：这里日期格式必须为 yyyy/mm/dd hh:mm:ss 才不会出现NaN这种现象。
    var b = '@ViewBag.EndTime';  //如果不是上面的那种格式可用replace来进行替换 var endTime = new Date(Date.parse(examEndTime.replace(/-/g, "/")));
        
    time_end = new Date(b);
    time_end = time_end.getTime();
    time_now_server = new Date(a);
    time_now_server = time_now_server.getTime();
    time_now_client = new Date();
    time_now_client = time_now_client.getTime();
    time_server_client = time_now_server - time_now_client;
    setTimeout("show_time()", 1000);

    function show_time() {
        var timer = document.getElementById("sp_lastTime");
        if (!timer) {
            return;
        }
        timer.innerHTML = time_server_client;
        //debugger
        var time_now, time_distance, str_time;
        var int_day, int_hour, int_minute, int_second;
        var time_now = new Date();
        time_now = time_now.getTime() + time_server_client;
        time_distance = parseInt(time_end - time_now);

        if (Number(time_distance) > 0) {
            int_day = Math.floor(Number(time_distance) / 86400000)
            time_distance -= int_day * 86400000;