flash actionscript倒计时日期差异返回NaN

Question

我正在创建一个简单的倒数计时器，其中正在从文本文件中读取日期。日期是纳秒格式。当计算两个日期之间的差异时，结果显示为NaN。 我尝试了trace(isNaN(currenttime))和trace(isNaN(targettime))，他们都返回false。然而，当我在timeleft上做同样的事情时，我得到了错误的含义，这意味着它不是一个有效的日期格式。这是我的代码。

提前感谢您的帮助。

//Loads variables from external file called data.txt
//yr2016 - April 18 2016 - 1460952000000
//yr2017 - April 18 2017 - 1492488000000
//yr2018 - April 17 2018 - 1523976000000
//yr2019 - April 15 2019 - 1555300800000
//yr2020 - April 15 2020 - 1586923200000
//yr2021 - April 15 2021 - 1618459200000
//yr2022 - April 15 2022 - 1649995200000

this.onEnterFrame = function() {

loadvariablesnum("data.txt",0);

var today:Date = new Date();
var currentyear = today.getFullYear();
var currenttime = today.getTime();

switch(currentyear) {
    case 2016:
    var targetdate:Date = new Date(yr2016);
    var targettime = targetdate.getTime();
    break;

    case 2017:
    var targetdate:Date = new Date(yr2017);
    var targettime = targetdate.getTime();
    break;

    case 2018:
    var targetdate:Date = new Date(yr2018);
    var targettime = targetdate.getTime();
    break;

    case 2019:
    var targetdate:Date = new Date(yr2019);
    var targettime = targetdate.getTime();
    break;

    case 2020:
    var targetdate:Date = new Date(yr2020);
    var targettime = targetdate.getTime();
    break;

    case 2021:
    var targetdate:Date = new Date(yr2021);
    var targettime = targetdate.getTime();
    break;

    case 2022:
    var targetdate:Date = new Date(yr2022);
    var targettime = targetdate.getTime();
    break;
}

    var timeLeft = targetTime - currentTime;

    var sec = Math.floor(timeLeft/1000);
    var min = Math.floor(sec/60);
    var hrs = Math.floor(min/60);
    var days = Math.floor(hrs/24);
    sec = String (sec % 60);
    if (sec.length < 2) {
        sec = "0" + sec;
    }
    min = String (min % 60);
    if (min.length < 2) {
        min = "0" + min;
    }
    hrs = String (hrs % 24);
    if (hrs.length < 2) {
        hrs = "0" + hrs;
    }
    days = String(days);

    var counter:String = days + ":" + hrs + ":" + min + ":" + sec;
    time_txt.text = counter;
}