Calculating year, month, days between dates in google apps script

Question

I have calculated using the below function and it gives the o/p in the format of "X YEARS, Y MONTHS, Z DAYS" and for some dates its giving some wrong o/p. I think I did some calculation missing in the formulas.

The function is,

/**
 * @param {Date} startdate
 * @param {Date} enddate
 * @return {String}
 */
function leasePeriodCalc(startDate,endDate)
{
  var sdate=startDate;
  var edate=endDate;
  edate.setDate( edate.getDate()+1);
  edate=new Date(edate);
  if(sdate.valueOf()>edate.valueOf()){
    return('0');
  }
  else{
    var years=((((edate.getDate()-sdate.getDate())<0 ? -1:0)+((edate.getMonth()+1)-(sdate.getMonth()+1)))< 0 ? -1 : 0)+(edate.getFullYear()-sdate.getFullYear());
    var months=((((edate.getDate()-sdate.getDate())<0 ? -1:0)+((edate.getMonth()+1)-(sdate.getMonth()+1)))< 0 ?12:0)+((edate.getDate()-sdate.getDate())<0 ? -1:0)+((edate.getMonth()+1)-(sdate.getMonth()+1));
    if((edate.getMonth()-1)!=1.0)
    {
      var days=((edate.getDate()-sdate.getDate())< 0 ?new Date(edate.getFullYear(), edate.getMonth(),0).getDate():0)+(edate.getDate()-sdate.getDate());
    }
    else
    {
      var days=((edate.getDate()-sdate.getDate())< 0 ?new Date(edate.getFullYear(), edate.getMonth()+1,0).getDate():0)+(edate.getDate()-sdate.getDate());
    }
    var day;
    var month;
    var year;
    if(years>1)year= years+ 'Years';
    else year=years+'Year';
    if(months>1) month= months+ 'Months';
    else month=months+'Month';
    if(days>1) day= days+ 'Days';
    else day=days+'Day';
    if(years==0&&months!=0&&days!=0) return(month+', '+day);
    else if(years!=0&&months==0&&days!=0) return(year+', '+day);
    else if(years!=0&&months!=0&&days==0) return(year+', '+month);
    else if(years==0&&months==0&&days!=0) return(day);
    else if(years==0&&months!=0&&days==0) return(month);
    else if(years!=0&&months==0&&days==0) return(year);
    else if(years==0&&months==0&&days==0) return(day);
    else if(years!=0&&months!=0&&days!=0) return(year+', '+month+', '+day);
  }
}

if you gives the i/p as below it returning the false o/p:

28th feb 2013 - 28th feb 2014

Expected o/p : 1 YEAR , 1 DAY

Given o/p : 1 YEAR , 4 DAYS

But if I select 28th feb 2013 - 27th feb 2014 means, It gave the correct o/p:

Expected o/p : 1 YEAR

Given o/p : 1 YEAR

Please advice to correct my fault if I did anything.

And also I have to tell that I'm not setting the rules n all. In general a month is calculating as per the days lying on the month.

For example, If we get a loan from a bank we ll pay the interest per month only even that month may have 30 days or 29 days or 28 days or 31 days.

And also if we take a room for monthly rental means, We ll pay the rent per month only rite? even it can be from 20th March - 19th April. Even it contains 31 days it is said to be one month only. Please help me to conclude this.

Tnx, CL.

Answer 1

For complex date/time manipulations in JavaScript I find that the Moment.js library can really help. I wrapped it up into an Apps Script library, which you can include using the project key MHMchiX6c1bwSqGM1PZiW_PxhMjh3Sh48. I used it to take a crack at this problem, although I may have missed some edge cases.

// Load the library (key: MHMchiX6c1bwSqGM1PZiW_PxhMjh3Sh48).
var moment = Moment.load();

function getDuration(startDate, endDate) {
  var start = moment(startDate);
  var end = moment(endDate);
  var units = ['years', 'months', 'days'];
  var parts = [];
  units.forEach(function(unit, i) {
    var diff = Math.floor(end.diff(start, unit, true));
    if (diff > 0 || i == units.length - 1) {
      end.subtract(unit, diff);
      parts.push(diff + ' ' + unit);
    }
  })
  return parts.join(', ');
}