function showBlock(id) {
  if (document.getElementById(id).className == "hidden") {
    document.getElementById(id).className="";
    document.getElementById("firma").checked=true;
    return false
  }
  if (document.getElementById(id).className != "hidden") {
    document.getElementById("firma").checked=false;
    document.getElementById(id).className="hidden";
    return false
  }
}

function preloader() {
 heavyImage = new Image(); 
 heavyImage.src = "images/box3_over.png";
 heavyImage2 = new Image(); 
 heavyImage2.src = "images/box4_over.png";
 heavyImage3 = new Image(); 
 heavyImage3.src = "images/submit2_over.png";
 heavyImage4 = new Image(); 
 heavyImage4.src = "images/submit_over.png";
 heavyImage5 = new Image(); 
 heavyImage5.src = "images/arrow_left_over.png";
 heavyImage6 = new Image(); 
 heavyImage6.src = "images/arrow_right_over.png";
 heavyImage7 = new Image(); 
 heavyImage7.src = "images/kontakt_button_over.png";
 heavyImage8 = new Image(); 
 heavyImage8.src = "images/box0_over.png";
}

function change_span() {
  if (document.getElementById("changeSpan").className == "special_span") {
    document.getElementById("changeSpan").className = "special_span2";
    document.getElementById("changeSpanArea").className = "spec_area_top2";
    document.getElementById("changeSpan").innerHTML = "Klikněte zde pro zavření formuláře";
    return false
  }
  else if (document.getElementById("changeSpan").className == "special_span2") {
    document.getElementById("changeSpan").className = "special_span";
    document.getElementById("changeSpanArea").className = "spec_area_top";
    document.getElementById("changeSpan").innerHTML = "Klikněte zde pro položení dotazu";
    return false
  }

}
function validEmail(email)
{
  invalidChars = " /:,;"

  if(email == "")
  {
    return false
  }
  for(i=0; i < invalidChars.length; i++)
  {
    badChar = invalidChars.charAt(i)
    if (email.indexOf(badChar,0) > -1)
    {
      return false
    }
  }
  atPos = email.indexOf("@",1)
  if(atPos == -1)
  {
    return false
  }
  if(email.indexOf("@",atPos+1) > -1)
  {
    return false
  }
  periodPos = email.indexOf(".",atPos)
  if(periodPos == -1)
  {
    return false
  }
  if(periodPos+3 > email.length)
  {
    return false
  }
  return true
}
function validPhone(phonenumber) {
  vyraz = /^[+]?[()/0-9. -]{9,}$/
  if (vyraz.test(phonenumber)==true)
    return true;
  else 
    return false;
}