title: toOrdinalSuffix tags: math,intermediate

Adds an ordinal suffix to a number.

Use the modulo operator (%) to find values of single and tens digits. Find which ordinal pattern digits match. If digit is found in teens pattern, use teens ordinal.

const toOrdinalSuffix = (num) => {
  const int = parseInt(num),
    digits = [int % 10, int % 100],
    ordinals = ["st", "nd", "rd", "th"],
    oPattern = [1, 2, 3, 4],
    tPattern = [11, 12, 13, 14, 15, 16, 17, 18, 19];
  return oPattern.includes(digits[0]) && !tPattern.includes(digits[1])
    ? int + ordinals[digits[0] - 1]
    : int + ordinals[3];
};

toOrdinalSuffix("123"); // "123rd"