var username = document.getElementById('username').value;
var password = document.getElementById('password').value;
var password2 = document.getElementById('password-2').value;

var re = /^\w{3,10}$/;
if (!re.test(username)) {
  alert("wrong username!");
  return false;
}  else if (password.length<6 || password.length>20) {
  alert("wrong password!");
  return false;
}  else if (password != password2) {
  alert("passwords don't match!");
  return false;
}  else {
  return true;
}
}