Calculate Kaprekar's Constant

kaperkar.js

function isSame(str1, str2) {
  return String(str1).split('').sort().join('') === String(str2).split('').sort().join('')
}
function kaprekar(num, seed = num, iterations = 0) {
  const digits = String(num).padStart(String(seed).length, '0').split('')
  const big = Number(digits.sort().reverse().join(''))
  const small = Number(digits.sort().join(''))
  const diff = big - small
  if (isSame(num, diff)) return console.log(seed, iterations, diff)
  kaprekar(diff, seed, iterations + 1)
}

for (let i = 100; i <= 999; i++) {
  kaprekar(i)
}