/**
 * @param {string[]} emails
 * @return {number}
 */
var numUniqueEmails = emails => {
    return emails.reduce((validMails, mail) => {
      const names = mail.split('@');
      let [local, domain] = names;
      const iPlus = [...local].findIndex(x => x === '+');
      if (iPlus !== -1) { local = local.substr(0, iPlus); }
      const key = local.split('.').join('') + '@' + domain;
      if (!validMails.has(key)) { validMails.add(key); }
      return validMails
    }, new Set).size;
};

/**
 * @param {string[]} emails
 * @return {number}
 */
var numUniqueEmails2 = emails => {
  const validMails = new Set();
  for (const mail of emails) {
    let [local, domain] = mail.split('@');
    const iPlus = [...local].findIndex(x => x === '+');
    if (iPlus !== -1) { local = local.substr(0, iPlus); }
    const key = [...local].filter(x => x !== '.').join() + '@' + domain;
    if (!validMails.has(key)) { validMails.add(key); }
  }
  return validMails.size;
};

/**
 * @param {string[]} emails
 * @return {number}
 */
var numUniqueEmails3 = emails => {
  const validMails = new Set();
  for (const mail of emails) {
    let [local, domain] = mail.split('@');
    local = local.replace(/+(.*)$/, '')
      .replace(/./g, '');
    console.log(local);
    const key = `${local}@${domain}`;
    if (!validMails.has(key)) { validMails.add(key); }
  }
  return validMails.size;
};

const names = mail.split('@');
  let [local, domain] = names;

let [local, domain] = mail.split('@');