Get GitHub emails from current repository

get-emails.js

javascript: (() => {
  const regex = /^https:\/\/github\.com\/([a-zA-Z0-9-_.]+\/[a-zA-Z0-9-_.]+)/g;
  const regexMatch = regex.exec(window.location.href);

  if (!regexMatch) {
    alert('Wrong site, use this script in a URL like: https://github.com/user/repository-name');

    return;
  }

  const userName = regexMatch[1];

  fetch(`https://api.github.com/repos/${userName}/branches`)
    .then(response => response.json())
    .then(data => {
      const urls = data.map(branch => `https://api.github.com/repos/${userName}/commits/${branch.name}`);

      Promise.all(urls.map(url => fetch(url)))
      .then(responses => Promise.all(
        responses.map(response => response.json())
      ))
      .then(result => {
        const emails = result.map((obj) => obj.commit.author.email);

        const emailList = emails.filter(function(email, index) {
          return emails.indexOf(email) === index;
        }).join(', ');

        alert(emailList);
      });
    });
})();