Resposta do Desafio #1

decoder.ts

const decode = (input: string) => {
  const chars = input.trim().replace(/\n/g, '');
  const data = Buffer.from(chars, 'base64').toString('utf-8');
  const payload = JSON.parse(data);
  const dic = Buffer.from(payload.dic, 'base64').toString('utf-8');
  const letters = payload.message.split(',').map((char: string) => dic[Number(char)]);
  return letters.join('');
}

encoder.ts

const encode = (input: string) => {
  const chars = input.toLowerCase().split('');
  const set = new Set(chars);
  const dic = [...Array.from(set)].sort(() => Math.random() > .5 ? 1 : -1).join('')
  const message = chars.map(c => dic.indexOf(c)).join(',');
  const payload = JSON.stringify({dic: Buffer.from(dic).toString('base64'), message});
  const stringData = Buffer.from(payload).toString('base64');
  return stringData.match(/.{1,64}/g)?.join("\n") as string;
}