function email(username) {
  return username + '@' + 'thirstylight' + '.' + 'com';
}

function writeEmailOpener(username) {
  document.write('<a href="mailto:' + email(username) + '">');
}

function writeEmailLink(username) {
  writeEmailOpener(username);
  document.write(email(username));
  document.write('</a>');
}