function obnov(menu) {
  
  page = "";    
     
  if(document.menu.order_by[0].checked) 
  order_by = "asc";
  else order_by = "desc";
  
  tridit = document.menu.tridit.options[document.menu.tridit.selectedIndex].value;      
  
  x  = 'index.php?page='+page+'&tridit='+tridit+'&order_by='+order_by;
  
  window.location=(x);
}

function show_filtr_byty() {

  document.getElementById('filtr_byty').style.display = 'block';

}

function hide_filtr_byty() {

  document.getElementById('filtr_byty').style.display = 'none';

}

function checkForm()
{
  var result = true;
  var error = "";
  
  var cena_od = document.form.cena_od.value;
  var cena_do = document.form.cena_do.value;
  
  if(cena_od != "")
  {
    if(isNaN(Number(cena_od)))
    {
      error += "Cena od není číslo!\n";
      result = false;
    }
  }
  
  if(cena_do != "")
  {
    if(isNaN(Number(cena_do)))
    {
      error += "Cena do není číslo!\n";
      result = false;
    }
  }
  
  if(!result)
  {
    alert(error);
  }
  
  return result;
}

function check_dotaz_k_nabidce() {

  var err = "";
  
  if(document.form.telefon.value == "") {
    
    err = "Telefon není vyplněn! \n";
  }
  
  if( err == "" ) {
  
    return true;
  } else {
  
    alert( err );
    return false;
  }
  
}