ArrayBuffer to Base64 packing and unpacking

browser_base64.js

const _fromCharCode = String.fromCharCode
export function pack_base64(arr) {
  let res=''
  const u8 = new Uint8Array(arr.buffer || arr)
  const len = u8.byteLength
  for (let i=0; i<len; i++)
    res += _fromCharCode(u8[i])
  return window.btoa(res)
}

const _charCodeAt = ''.charCodeAt
export function unpack_base64(str_b64) {
  const sz = window.atob(str_b64)
  const len = sz.length
  const res = new Uint8Array(len)
  for (let i=0; i<len; i++)
    res[i] = _charCodeAt.call(sz, i)
  return res
}

test.js

function test(count=1, width=64) {
  if (0 > width) width = 0 | 1 - width * Math.random()

  while (--count > 0) {
    const b0 = new Uint8Array(width)
    window.crypto.getRandomValues(b0)
    const sz_b64 = pack_base64(b0)
    const b1 = unpack_base64(sz_b64)
    const b2 = Array.from(b0, (v,i) => ((b1[i] - v) || ''))
    console.log(b2.join('.'))
  }
}

console.log()
test(10, 63)

console.log()
test(10, 64)

console.log()
test(10, 65)