Get the ordinal suffix for any number you want converted to a day. ie. suffixes -st, -nd, -rd, -th in written ordinals (represented as 1st, 2nd, 3rd, 4th)

ordinalSuffix.js

function ordinalSuffix(i) {
  const j = i % 10,
      k = i % 100;
  if (j === 1 && k !== 11) {
      return i + 'st';
  }
  if (j === 2 && k !== 12) {
      return i + 'nd';
  }
  if (j === 3 && k !== 13) {
      return i + 'rd';
  }
  return i + 'th';
}