standard test fail (possible bug)

base64.js

function characterRange (minCharacter, maxCharacter) {
  const lower = minCharacter.charCodeAt(0)
  const upper = maxCharacter.charCodeAt(0)

  return Array(upper - lower + 1)
    .fill()
    .map((_, index) => String.fromCharCode(lower + index))
    .join('')
}

const base64 =
  characterRange('A', 'Z') +
  characterRange('a', 'z') +
  characterRange('0', '9') +
  '+/'

const unbase64 = Array.from(base64)
  .reduce((table, character, index) => {
    table[character.charCodeAt(0)] = index
    return table
  }), { ['='.charCodeAt(0)]: 64 })