FCC Friendly Date Ranges Algorithm

function makeFriendlyDates(arr) {
  var months = ["January", "Febraury", "March", "April",
               "May", "June", "July", "August",
               "September", "October", "November", "December"];

  function ordinal(num){
    var end = "th";
    if (num % 10 == 1){
      end = "st";
    }else if (num % 10 == 2){
      end = "nd";
    }else if (num % 10 == 3 && num != 13){
      end = "rd";
    }
    return num + end;
  }

  var result = [];
  var one = arr[0].split('-');
  var two = arr[1].split('-');
  for (var i = 0; i<one.length; i++){
    one[i] = parseInt(one[i]);
  }
  for (var j = 0; j<two.length; j++){
    two[j] = parseInt(two[j]);
  }

  //year, month, day

  var date1 = new Date(one[0], one[1] - 1, one[2]);
  var date2 = new Date(two[0], two[1] - 1, two[2]);

  //used for testing
  //date1 = new Date(2022, 9 - 1, 5);
  //date2 = new Date(2023, 9 - 1, 4);

  var month2 = date2.getUTCFullYear()*12 + date2.getUTCMonth();
  var month1 = date1.getUTCFullYear()*12 + date1.getUTCMonth();

  var dayDiff = Math.abs(date2.getUTCDate() - date1.getUTCDate());
  var monthDiff = month2 - month1;
  var yearDiff = date2.getUTCFullYear() - date1.getUTCFullYear();

  //same day
  if (dayDiff === 0 && monthDiff === 0 && yearDiff === 0){
    return [months[date1.getUTCMonth()] + " " + ordinal(date1.getUTCDate()) + ", " +
      date1.getUTCFullYear()];
  }else if (monthDiff === 0 && date1.getUTCFullYear() == date2.getUTCFullYear()){
    //less than 12 months and same month and same year
    result.push(months[date1.getUTCMonth()] + " " + ordinal(date1.getUTCDate()));
    result.push(ordinal(date2.getUTCDate()));
    return result;
  }else if (monthDiff < 12 && date1.getUTCFullYear() == date2.getUTCFullYear()){
    //less than 12 months and same year
    result.push(months[date1.getUTCMonth()] + " " + ordinal(date1.getUTCDate()) + ", " +
      date1.getUTCFullYear());
    result.push(months[date2.getUTCMonth()] + " " + ordinal(date2.getUTCDate()));
    return result;
  }else if (monthDiff < 12){
    //less than 12 months
    result.push(months[date1.getUTCMonth()] + " " + ordinal(date1.getUTCDate()));
    result.push(months[date2.getUTCMonth()] + " " + ordinal(date2.getUTCDate()));
    return result;
  }else if (yearDiff == 1 && monthDiff == 12 && date1.getUTCDate() > date2.getUTCDate()){
    result.push(months[date1.getUTCMonth()] + " " + ordinal(date1.getUTCDate()) + ", " +
      date1.getUTCFullYear());
    result.push(months[date2.getUTCMonth()] + " " + ordinal(date2.getUTCDate()));
    return result;
  }else if (yearDiff >= 1){
    result.push(months[date1.getUTCMonth()] + " " + ordinal(date1.getUTCDate()) + ", " +
      date1.getUTCFullYear());
    result.push(months[date2.getUTCMonth()] + " " + ordinal(date2.getUTCDate()) + ", " +
      date2.getUTCFullYear());
    return result;
  }

}