如何从单元格中获取5位数字序列日期格式的字符串值到脚本中?

我在一个单元格中有一个公式，该公式通过合并电子表格中两个单元格的值来对另一个工作表进行vlookup.这是名称表，位于左侧，日期位于顶部.我将名称和日期值组合成一个字符串值，并将其作为vlookup键值使用，效果很好.现在，我基本上需要在Google脚本中执行相同的操作，但是日期值让我无所适从.在vlookup单元格公式中，日期值是5位数字的日期序列号.但是，当我在脚本中合并两个单元格值时，无法从单元格中获得相同的5位串行代码.我已经尝试了数字，字符串，文本等的所有转换.我可以使用什么函数在脚本中将这5位日期值作为字符串获取?

I have a formula in a cell that is doing a vlookup to another sheet by combining the values of two cells on my spreadsheet. It's a table of names on the left and dates up top. I'm combining the name and date values into a single string value and using that as by vlookup key value, which works great. Now I need to basically do the same thing in my google script, but the date value has me at a loss. In the vlookup cell formula, the date value is the 5 digit date serial code. However when I combine the two cell values in my script, I cannot get the same 5 digit serial code out of the cell. I have tried all conversions of number, string, text, ect. What function can I use to get this 5 digit date value as a string in my script?

function serialDatevalue(){
  var WB = SpreadsheetApp.getActiveSpreadsheet().getActiveSheet();
  var NewDate = new Date();
  var NewDate =  WB.getRange('B1').getValue();
  var JSdate =  WB.getRange('B1').getValue();
  Browser.msgBox(Number(NewDate));

// Some others that I have tried
//  var JSdate = Date.parse(DateValue);
//  var JSdate = Number(DateValue);
//  var JSdate = Utilities.formatDate(DateValue, 'PST', '%');
}

例如，2019年4月13日=43568.我想将此5位数字值作为字符串.

for example, April 13, 2019 = 43568. I want to get this 5 digit value as a string.

我不断收到'Sat Apr 13 2019 00:00:00 GMT-0700(PDT)'或其他更长的整数值.

I keep getting 'Sat Apr 13 2019 00:00:00 GMT-0700 (PDT)', or other longer integer values.

请帮助.