about Date operation no correct problem in google Appscript-CodePudding

  var lastrow = SS.getLastRow()
  var lastday = SS.getRange("A"  lastrow).getValue(); //Thu Dec 31 11:00:00 GMT-05:00 2009 = 2010-01-01 (GMT  8)
  var today = SS.getRange("C2").getValue();
  var diffInDays = Math.floor((today-lastday)/(24*3600*1000));

  //Creat DateAr |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
  Logger.log(diffInDays)
  var AddingAr =[]
  for (var i = 1; i < diffInDays ; i = i   1) {

    var d_date = new Date();
    d_date = d_date.setDate(lastday.getDate()  i )
    var d_dateString = Utilities.formatDate( new Date(d_date) , "GMT 8", "yyyy-MM-dd")
    AddingAr.push([d_dateString])
    Logger.log("lastday: "  lastday "  i:"  i   " =d_date: "  d_date  " = "   d_dateString)

  }

  Logger.log(AddingAr)
  Logger.log(AddingAr.length)
  SS.getRange(lastrow   1, 1,AddingAr.length).setValues(AddingAr)

as seem , //Thu Dec 31 11:00:00 GMT-05:00 2009 = 2010-01-01 (GMT 8) d_date = d_date.setDate(lastday.getDate() i ) //in for loop

2010-01-01 1 should be 2010-01-02 log:2022-09-02 2010-01-01 2 should be 2010-01-03

i have no idea why 2010-01-01 1 is 2022-09-02

Log:

lastday: Thu Dec 31 2009 11:00:00 GMT-0500 (Eastern Standard Time)  i:1 =d_date: 1662023267434 = 2022-09-01
下午5:07:47   資訊  lastday: Thu Dec 31 2009 11:00:00 GMT-0500 (Eastern Standard Time)  i:2 =d_date: 1662109667441 = 2022-09-02
下午5:07:47   資訊  lastday: Thu Dec 31 2009 11:00:00 GMT-0500 (Eastern Standard Time)  i:3 =d_date: 1662196067443 = 2022-09-03
下午5:07:47   資訊  lastday: Thu Dec 31 2009 11:00:00 GMT-0500 (Eastern Standard Time)  i:4 =d_date: 1662282467445 = 2022-09-04
下午5:07:47   資訊  lastday: Thu Dec 31 2009 11:00:00 GMT-0500 (Eastern Standard Time)  i:5 =d_date: 1662368867447 = 2022-09-05

CodePudding user response：

The javascript Date object only refers to the day of the month, not the whole date

new Date() does not create an empty date object, but it creates the date of today including the time in hours, minutes and seconds.
If you execute console.log(new Date()) today, it will result in something like Tue Aug 08 2022 07:44:012 GMT-0500 (Eastern Standard Time)
Then, for example console.log(new Date().setDate(10)) will result in Tue Aug 10 2022 07:44:012 GMT-0500 (Eastern Standard Time)
What you want instead is to create a date object from your existing timestamp: var d_date = new Date(lastday); instead of var d_date = new Date();
Then, the rest of your code will work - if lastday is a valid date object
For better understanding

function myTestFunction(){
  var SS = SpreadsheetApp.getActiveSheet();
  var lastrow = SS.getLastRow()
  var lastday = SS.getRange("A"  lastrow).getValue();
  var d_date = new Date(lastday);
  console.log(d_date);
  console.log(d_date.setDate(10));
}