Gerar CNPJ em JavaScript

const W1 = [5,4,3,2,9,8,7,6,5,4,3,2];
const W2 = [6,5,4,3,2,9,8,7,6,5,4,3,2];
const val = (c) => c.charCodeAt(0) - 48;        // '0'->0 ... 'Z'->42
const dvCNPJ = (base, w) => {
  let s = 0;
  for (let i = 0; i < w.length; i++) s += val(base[i]) * w[i];
  const r = s % 11;
  return r < 2 ? 0 : 11 - r;
};

function generateCNPJ({ alpha = false, mask = false } = {}) {
  const set = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
  let base = '';
  for (let i = 0; i < 8; i++)
    base += alpha ? set[Math.floor(Math.random() * 36)] : String(Math.floor(Math.random() * 10));
  base += '0001';
  const d1 = dvCNPJ(base, W1), d2 = dvCNPJ(base + d1, W2);
  const s = base + d1 + d2;
  return mask ? s.replace(/^(..)(...)(...)(....)(..)$/, '$1.$2.$3/$4-$5') : s;
}

generateCNPJ();                          // '11222333000181'  (numérico)
generateCNPJ({ mask: true });            // '11.222.333/0001-81'
generateCNPJ({ alpha: true });           // '12ABC34501DE35'  (alfanumérico)
generateCNPJ({ alpha: true, mask: true }); // '12.ABC.345/01DE-35'

function isValidCNPJ(cnpj) {
  cnpj = String(cnpj).replace(/[./-]/g, '').toUpperCase();
  if (!/^[A-Z0-9]{12}\d{2}$/.test(cnpj)) return false;
  if (/^(.)\1{13}$/.test(cnpj)) return false;
  const d1 = dvCNPJ(cnpj.slice(0, 12), W1);
  const d2 = dvCNPJ(cnpj.slice(0, 12) + d1, W2);
  return d1 === Number(cnpj[12]) && d2 === Number(cnpj[13]);
}

isValidCNPJ(generateCNPJ({ alpha: true })); // true