Made of little things.

/** Base64 for byte arrays of any size, without a string per byte on the way out. */
export function bytesToBase64(bytes) {
  let binary = '';
  const chunk = 0x8000;
  for (let i = 0; i < bytes.length; i += chunk) {
    binary += String.fromCharCode.apply(null, bytes.subarray(i, i + chunk));
  }
  return btoa(binary);
}

export function base64ToBytes(text) {
  const binary = atob(text);
  const bytes = new Uint8Array(binary.length);
  for (let i = 0; i < binary.length; i++) bytes[i] = binary.charCodeAt(i);
  return bytes;
}