finding the closest frakking number

stuff.js

function get_digit(n, d) {
  return Math.floor(n / Math.pow(10, d)) % 10
}

function is_unique(n, d) {
  let m = 0
  let c = Math.pow(10, d)

  for (let i = d; n > c; i++, c *= 10) {
    let new_m = m ^ (2 << get_digit(n, i) + 1)
    if (new_m < m) return false
    m = new_m
  }

  return true
}

function closest(a, b, n) {
  if (a == null) return b
  if (b == null) return a
  if (a > n) return b
  if (b > n) return a
  return n-a < n-b ? a : b
}

function _calc(n, d, orig_n) {
  if (d < 0) return is_unique(n, 0) ? n : null

  //console.log('calc', n, d)

  let max = Math.pow(10, d + 1)
  let try_n

  let above = null
  try_n = null
  for (let i = 1; i <= max; i *= 10) {
    for (let j = 0; j <= 9; j++) {
      let new_n = n + i*j
      let uniq = is_unique(new_n, d)
      if (uniq) {
        try_n = closest(try_n, new_n, orig_n)
      }
    }
  }
  if (try_n) {
    above = _calc(try_n, d - 1, orig_n)
  }

  let below = null
  try_n = null
  for (let i = 1; i <= max; i *= 10) {
    for (let j = 1; j <= 9; j++) {
      let new_n = n - i*j
      let uniq = is_unique(new_n, d)
      if (uniq) {
        try_n = closest(try_n, new_n, orig_n)
      }
    }
  }
  if (try_n) {
    below = _calc(try_n, d - 1, orig_n)
  }

  console.log('calc', n, d, '-', above, below)
  return closest(above, below, orig_n)
}

function calc(n) {
  if (n < 0) return -calc(-n)
  if (n > 10e10) return 9876543210
  return _calc(n, Math.ceil(Math.log(n) / Math.log(10)), n)

}

console.log('result', calc(5555555555))