49-js-filter-3.js

// Your friend saw the great work you did with keeping your user-names at bay in
// http://www.codewars.com/dojo/katas/525d9b1a037b7a9da7000905
// now he'd like you to do (nearly) the same thing for his website, but as always,
// the devil is in the details.
// He has troubles with users ending or starting in a ".", and his user-array is
// a flat array of user-email-pairs, like so:
// [ "foo", "foo@bar.com", "bar", "bar@foo.com", ".foo", "food@bar.com" ]
// He is only interested in e-mailing the users and ask them to sign up again, so
// no need to keep the user-name, only e-mail addresses for the user-names that start
// or end with a "." should be returned. For the above array, the correct return-array would be
// [ "food@bar.com" ]
// You have to use the filter-method of Javascript, which returns each element of the array for
//  which the filter-method returns true. The second argument gives the index you're looking at
//   and the third argument is the array itself:
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter

export default (logins) => {
  const withDot = logins.filter(e => e[0] === '.' || e[e.length - 1] === '.').map(e => (e[0] === '.' ? e.slice(1) : e.slice(0, -1)));
  const emails = logins.filter(e => e.includes('@'));
  return emails.filter(e => !!withDot.find(el => e.slice(0, e.indexOf('@')).includes(el)));
};