Google Apps Script: Number of days between two dates after subtracting full months

Question

I have two dates. I would like to know a) the number of full months between the two dates and b) the number of days after subtracting the full months.

Essentially what DATEDIF(start_date, end_date, "m") and DATEDIF(start_date, end_date, "md") would do if entered as a formula in Google Sheets.

Example: Start date is 18 November 2015 End date is 3 March 2016

The number of full months between the two dates is 3. The number of days after subtracting the full months is 12 + 3 = 15.

Does anyone have a solution how to calculate this in Google Apps Script?

Thanks for pointing me to this post, Amit. I had already seen it; unfortunately, it only partially answers my question. I haven't seen a full answer in any of the forums I searched. — Fabian Müller, Sep 22 '16 at 16:21
do show us first what you tried in javascript, like in the linked suggestion. — Zig Mandel, Sep 22 '16 at 22:55

score 2 · Answer 1 · answered Sep 23 '16 at 13:39

To get the number of days after subtracting the full months, use this code:

function getNumberOfDaysBetweenTwoDatesSubstractFullMonths(startDate, endDate) {

  var startDay = startDate.getDate();
  var startMonth = startDate.getMonth();
  var startYear = startDate.getYear();

  var endDay = endDate.getDate();

  var startNumber = daysInMonth(startMonth, startYear) - startDay;
  var endNumber = endDay;

  return startNumber + endNumber;

}

function daysInMonth(month, year) {
  return new Date(year, month + 1, 0).getDate();
}

To check this in Google Sheets Script:

function TEST_days() {
  var d1 = new Date('18 November 2015');
  var d2 = new Date('3 March 2016');

  Logger.log(getNumberOfDaysBetweenTwoDatesSubstractFullMonths(d1, d2));

}

Google Apps Script: Number of days between two dates after subtracting full months

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