function preventDefault(event) {
  if(event.preventDefault) event.preventDefault();
  else event.returnValue = false;
}

function itemOn(event, item) {
  item.firstChild.firstChild.src = 'images/laziska/mainmenu-knob-on.png'
}

function itemOff(event, item) {
  item.firstChild.firstChild.src = 'images/laziska/mainmenu-knob-off.png'
}

function auth(event, target) {
  preventDefault(event)
  var form = event.target ? (event.target instanceof HTMLFormElement ? event.target : event.target.form) : target
  var login = form.elements[0]
  var passwd = form.elements[1]
  var submit = form.elements[2]
  var badcred = document.getElementById('badcred')
  login.setAttribute('readonly', 'readonly')
  passwd.setAttribute('readonly', 'readonly')
  submit.setAttribute('disabled', 'disabled')
  badcred.style.visibility = 'hidden'
  var al = new AjaxLoader()
  al.load(form.action, function() {
    if(Number(al.responseText)) {
      location = '.'
    } else {
      badcred.style.visibility = 'visible'
      login.removeAttribute('readonly')
      passwd.removeAttribute('readonly')
      submit.removeAttribute('disabled')
    }
  }, 'login='+login.value+'&passwd='+passwd.value)
}