function emailEncodeLenght(addressLength) {
  let result = '';
  let x = addressLength;
  for (var i = 0; i < x; i++ ) {
    if (i <= x) {
      result += '*'
    }
  }
  return result;
}

function protectEmail(userEmail) {
  var avg, splitted, part1, part2;
  splitted = userEmail.split("@");
  part1 = splitted[0];
  avg = part1.length -1;
  part1 = part1.substring(0, (part1.length - avg));
  part2 = splitted[1];
  return part1 + emailEncodeLenght(splitted[0].length -1) + part2;
};


protecEmail('someemailaddress@gmail.com') //output: s***************@gmail.com