.map function not working with .slice in google scripts

Question

I am trying to standardise the formatting of today's date, and date's listed on a google sheet. In order to do this, I have pulled the column's into an array, and am trying to map & slice to get rid of the times on the end of a date. However, the slice is simply returning the first 11 data points. Ie it is not slicing the individual strings, and instead the array as a whole. Any help would be great, as I am very knew to the function.

function getDateColum(){
  var ss = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Rota")
  var dateHeaders = ss.getRange('E3:ND3').getValues();
  var date = new Date()
  date = date + ""
  date = date.slice(0,11)
  dateHeaders = dateHeaders.map(function(x){ return x.slice(0,11); })
  Logger.log(date)
  Logger.log(dateHeaders)
}

Answer 1

Thanks all for your help. This is what ended up working due to the data types, in case anyone sees this later

 function getDateColum(){ var ss = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Master Rota") var dateHeaders = ss.getRange('E3:ND3').getValues(); var date = new Date() date = date + "" date = date.slice(0,11) dateHeaders = dateHeaders[0].map(function(x){ return x.toString().substring(0, 11) }) Logger.log(dateHeaders) Logger.log(date)

Thanks again