064-how-old-will-i-be-in-2099.js

// Philip's just turned four and he wants to know how old he will be in
// various years in the future such as 2090 or 3044. His parents can't keep up
// calculating this so they've begged you to help them out by writing a
// programme that can answer Philip's endless questions.

// Your task is to write a function that takes two parameters: the year of
// birth and the year to count years in relation to. As Philip is getting more
// courious every day he may soon want to know how many years it was until he
// would be born, so your function needs to work with both dates in the future
// and in the past.

// Provide output in this format: For dates in the future: "You are ...
// year(s) old." For dates in the past: "You will be born in ... year(s)." If
// the year of birth equals the year requested return: "You were born this
// very year!"

// "..." are to be replaced by the number, followed and proceeded by a single
// "..." space. Mind that you need to account for both "year" and "years",
// "..." depending on the result.

// Good Luck!

function  calculateAge(y1, y2) {
  let dif = y2 - y1;
  let year = dif == 1 || dif == -1 ? "year" : "years";
  if (y1 < y2) {
    return `You are ${dif} ${year} old.`
  } else if (y2 < y1) {
    return `You will be born in ${-dif} ${year}.`
  } else {
    return "You were born this very year!"
  }
}