function ZkontrolujPrihlaseni()
{
    var form=document.forms["loginForm"];
    if(form.login.value.length<6)
        {
        alert(phrases["login"]+" "+phrases["tooshort"]);
        form.login.focus();
        return false;
        }
    if(form.password.value.length<6)
        {
        alert(phrases["password"]+" "+phrases["tooshort"]);
        form.password.focus();
        return false;
        }
   
    try
     {
         var xhr=new XMLHttpRequest();
         xhr.open("post","introduction/script_php/login.php",false);
         xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
         xhr.onreadystatechange=function()
            {
                 if(xhr.readyState==4)
                 {
                      if(xhr.status == 200)
                        {
                         var pole=xhr.responseText.split('-');
                         if(pole[0]=="true")
                         {
                             window.sessionStorage.setItem("user_id",pole[1]);
                             var cookieId="userId="+pole[1];
                             var datum = new Date();
                             datum.setTime(datum.getTime()+604800000);
                             var cookieExp=";expires="+datum;
                             var cookie=cookieId+cookieExp;
                             document.cookie=cookie;
                             location="main";
                             return false;
                            }
                        else
                        {
                            if(pole[1]=="no_exist")
                                alert("špatný heslo bo nick");
                            else
                                alert("účet nevalidní");
                          return false;
                        }
                      }
                    else
                      {
                        alert(phrases["connerror"]+"..."+xhr.responseText);
                        return false;
                      }
                }
        }
    var data=encodeNameAndValue("login",form.login.value)+"&";
    data+= encodeNameAndValue("heslo",form.password.value)+"&";
    xhr.send(data);
  }
  catch(e)
  {
    alert(phrases["connerror"]);
    return false;
  }
  return false;
}
function clickclear(field,defaulttext)
{
  if (field.value == defaulttext)
  {
    field.value = "";
  }
}
function clickrecall(field, defaulttext)
{
  if (field.value == "")
  {
    field.value = defaulttext;
  }
}