Code to convert birthdate in months/years to age in months/years and vice versa

convertAgeBirthdateYearMonths.js

/* Converts between age in years/months and birthdate years/months. */
// You will be blown at how this piece of art works!


const CURRENT_YEAR = new Date().getFullYear();      // rightnow: 2019
const CURRENT_MONTH = new Date().getMonth() + 1;    // rightnow: 8 (august)

const convertAgeBirthdateYearMonths = (month = null, year = null) => {
  const deltaAmount = (CURRENT_YEAR - year) * 12 + CURRENT_MONTH - month;
  const convertedMonth = deltaAmount % 12;
  const convertedYear = (deltaAmount - convertedMonth) / 12;
  return {convertedMonth, convertedYear};
};

console.log(convertAgeBirthdateYearMonths(2,1));    // 1 year 2 months old => {6, 2018} - Jun 2018
console.log(convertAgeBirthdateYearMonths(6,2018))  // 6/2018 => {1, 2} - 1 year 2 months old