leapyear.js

function isLeapYear(year) {
  if(year > 1582 && divisibleBy4(year)) {
    if(divisibleBy100ButNot400(year)) {
      return false;
    } else {
      return true;
    }
  } else {
    return false;
  }
}

function divisibleBy100ButNot400(year) {
  return divisibleBy100(year) && notDivisibleBy400(year)
}

function divisibleBy(year, by) {
  return year % by === 0;
}

function divisibleBy4(year) {
  return divisibleBy(year, 4);
}

function divisibleBy100(year) {
  return divisibleBy(year, 100);
}
function notDivisibleBy400(year) {
  return !divisibleBy(year, 400);
}

// function longIf(year) {
//   if(year > 1582 && year % 4 === 0 && (year % 100 === 0 && year % 400 !== 0) ||  {
// }


console.log('2000', isLeapYear(2000) === true)
console.log('2004', isLeapYear(2004) === true)
console.log('2003', isLeapYear(2003) === false)
console.log('1900', isLeapYear(1900) === false)