Custom base32 generator

index.js

const ALPHABET = "RKYM5C4H07P9EGWJ1BZQ8V3S62FXNTDA"
const BASE_LENGTH = ALPHABET.length
const SHORT_CODE_LENGTH = 6

function toBase (input) {
  let number = input

  if (number === 0) {
    return ALPHABET[0] 
  }

  let result = ''

  while (number > 0) {
    const rest = number % BASE_LENGTH
    result = `${ALPHABET[rest]}${result}`
    number = Math.floor(number / BASE_LENGTH)
  }

  return result
}

function generateShortCode (input) {
  const lower = Math.pow(BASE_LENGTH, SHORT_CODE_LENGTH - 1)
  const upper = Math.pow(BASE_LENGTH, SHORT_CODE_LENGTH) - 1
  const range = upper - lower
  const size = 1E2
  const offset = Math.floor(range / Math.min(size, range))
  const number = lower + (offset * input)

  return toBase(number)
}

console.log(generateShortCode(1))
console.log(generateShortCode(2))
console.log(generateShortCode(3))
console.log(generateShortCode(4))
console.log(generateShortCode(5))
console.log(generateShortCode(6))
console.log(generateShortCode(7))
console.log(generateShortCode(8))
console.log(generateShortCode(9))
console.log(generateShortCode(10))

// K7TWYB
// KQFNCY
// KT6PHQ
// YHV6P5
// YBQ4EV
// YX18J4
// MCWYBS
// MJ9180
// M20D32
// 5M4E2P