Rate my Friendly Date Ranges algorithm

Rate my Friendly Date Ranges algorithm
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#1

I would like if someone could take a look at my Friendly Date Ranges algorithm and give me a feedback.
My approach was to solve one testing case at a time. Firstly I’ve checked if the years are equal, returned the corresponding values, if not, returned the corresponding values. And so on…

I know that there is a better approach and I would like to learn it :slight_smile:
Also my if/else statements are probably hard to understand, I apologize for that.

function makeFriendlyDates(arr) {
  
  //Getting the date out of the input
  var startingDate = arr[0].split("-");
  var endindDate = arr[1].split("-");
  
  //Setting the initial starting date
  var sDay = startingDate[2],
      sMonth = startingDate[1],
      sYear = startingDate[0];
  
  //Setting the initial ending date
  var eDay = endindDate[2],
      eMonth = endindDate[1],
      eYear = endindDate[0];
  
  //Setting an array of the months names, added a dummy array at index 0.
  var months = ["free because index 0",
                "January","February","March",
                "April","May","June",
                "July","August","September",
                "Octomber","November","December"];
  
  //Converting the years to integers.
  sYear = parseInt(sYear);
  eYear = parseInt(eYear);
  
  //Converting the date's month to literal.
  sMonth = months[parseInt(sMonth)];
  eMonth = months[parseInt(eMonth)];
  
  //Converting the days.
  sDay = changeDayFormat(sDay);
  eDay = changeDayFormat(eDay);
  
  //Conditions:
  if(sYear === eYear){
    if(sMonth === eMonth){
      if(sDay === eDay){
        return [sMonth + " " + sDay + ", " + sYear];
      }
      return [sMonth + " " + sDay, eDay];
    }
    else if(sMonth !== eMonth){
      return [sMonth + " " + sDay + ", " + sYear, eMonth + " " + eDay];
    }
  } else {
    if(sMonth === eMonth && parseInt(sDay) > parseInt(eDay)){
      return [sMonth + " " + sDay + ", " + sYear, eMonth + " " + eDay];
    } 
    
    if(months.indexOf(sMonth) > months.indexOf(eMonth) && sYear+1 == eYear) {
      return [sMonth + " " + sDay, eMonth + " " + eDay];
    }
    return [sMonth + " " + sDay + ", " + sYear, eMonth + " " + eDay + ", " + eYear];
  }
    
}

function changeDayFormat(day) {
  day = parseInt(day);
  if(day === 1){
    day+="st";
  } else if(day === 2){
    day+="nd";
  } else if(day === 3){
    day+="rd";
  } else {
    day+="th";
  }
  
  return day;
}

makeFriendlyDates(["2016-01-01", "2016-12-31"]);

#2

Your function will return 21th, 22th, 23th, 31th.

Tests doesn’t check this edge case, yet: