function joinleave(n) {
  if (n==0) {
    document.getElementById("btnjoin").value="Join";
    document.getElementById("btnleave").value="";
  } else if (n==1) {
    document.getElementById("btnjoin").value="";
    document.getElementById("btnleave").value="Leave";
  }
}

function mailform() {
  var email=document.getElementById("email").value;
  if (email.length<1) {
    alert("Please enter your E-Mail address!");
    return false;
  }
  if (email.indexOf("@")<1) {
    alert("You must enter a valid E-Mail address!");
    return false;
  }
  var zipcode=document.getElementById("zipcode").value;
  if (zipcode.length<1) {
    alert("Please enter your Zip or postal code!");
    return false;
  }
  return true;
}