function Zabal(){
  var menu = document.getElementById("menu");
  menu.style.display='none';
  
  var tlac = document.getElementById("schovej");
  tlac.style.display='none';
  
  var sl1 = document.getElementById("sloupec1");
  sl1.style.display='none';

  var sl2 = document.getElementById("sloupec2");
  sl2.style.display='none';

  var sl3 = document.getElementById("sloupec3");
  sl3.style.display='none';
  
  var tlac = document.getElementById("ukaz");
  ukaz.style.display='block';
}   

function Rozbal(){
  var menu = document.getElementById("menu");
   menu.style.display='block';

  var tlac = document.getElementById("ukaz");
  ukaz.style.display='none';
  
  var sl1 = document.getElementById("sloupec1");
  sl1.style.display='block';

  var sl2 = document.getElementById("sloupec2");
  sl2.style.display='block';

  var sl3 = document.getElementById("sloupec3");
  sl3.style.display='block';  
  
  var tlac = document.getElementById("schovej");
  tlac.style.display='block';

  }   

  
function CheckForm(){
  X = document.forms['platit'];
  if(X.jmeno.value == ""){
    alert("The field Name is required.");
    X.jmeno.focus();
    return false;
  }  
  if(X.adresa.value == ""){
    alert("The field Adress is required.");
    X.adresa.focus();    
    return false;
  }    
  if(X.email.value == ""){
    alert("The field E-mail is required.");
    X.email.focus();    
    return false;
  }    
  if(X.cc_number.value == ""){
    alert("The field Credit card number is required.");
    X.cc_number.focus();    
    return false;
  }      
  if(X.cc_holder.value == ""){
    alert("The field Credit card holder is required.");
    X.cc_holder.focus();    
    return false;
  }
  if(X.cc_cvvcvc.value == ""){
    alert("The field Credit card CVV/CVC code is required.");
    X.cc_cvvcvc.focus();    
    return false;
  }      
  return true;
}

function kontrola_povinne_polozky(polozka, text) {

  if (document.getElementById(polozka).value.length == 0) {
    alert (text);
    document.getElementById(polozka).focus();
    return false;
  }
  return true;
}

function kontrola_email(polozka, text){
  var str=document.getElementById(polozka).value;
  if (window.RegExp) {
    filter = new RegExp("^[a-zA-Z0-9_\.\-]+\@[a-zA-Z0-9\-\.]+\.[a-zA-Z0-9]{2,4}$");
  }
  //  var filter=/^([\w-]+(?:\.[\w-]+)*)@((?:[\w-]+\.)*\w[\w-]{0,66})\.([a-z]{2,6}(?:\.[a-z]{2})?)$/i;

  if (!filter || filter.test(str) || (document.getElementById(polozka).value.length == 0)) {
    return true;
  } else {
    alert(text);
    document.getElementById(polozka).focus();
    return false;
  }
}