korzha

//const pattern = 'XXXXXXXXXXXXIIXXXX'
const digitsRe = new RegExp('/^\d+$/')

function test(str) {
  if (str.length == 0) return false
  // part 1: check that first at most 12 characters are only numbers
  let end = Math.min(12, str.length)
  if !digitsRe.test(str.substring(0, end)) return false
  // part 3: check that at most 4 characters after 12 digits and 2 any chars are only numbers
  end = Math.min(12 + 2 + 4, str.length)