document.getElementById('loginform').onsubmit = function() {
  var fields = document.getElementsByTagName('input');
  var retval = false;

  for (var i = 0; i < fields.length; i++)
  {
    if (fields[ i ].name == 'name')
    {
      if (fields[ i ].value == '')
      {
        error = set_error(1);
      }
    }

    if (fields[ i ].name == 'email')
    {
      var filter = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;

      if (fields[ i ].value == '')
      {
        error = set_error(2);
      }
      else if (!filter.test(fields[ i ].value))
      {
        error = set_error(3);
      }
    }

    if (error == true)
    {
      retval = true; 
    }
  }

  return (retval == true) ? false : true;
}

function set_error(error_id) {
  if (error_id == 1)
  {
    alert('Prosim zadajte Vase meno');
  }
  else if (error_id == 2)
  {
    alert('Prosime zadajte Vas email');
  }
  else if (error_id == 3)
  {
    alert('Zadali ste zlu emailovu adresu');
  }

  return true;
}