var ajax = new Ajax();

var nSlide = 1;
var nMax = 25;


var getDemo = function(nSlide) {
  var prevBtn = document.getElementById('prevBtn');
  var nextBtn = document.getElementById('nextBtn');
    if (nSlide == 1) {
      prevBtn.style.visibility = "hidden";
    }
    else {
      prevBtn.style.visibility = "visible";
    }
    if (nSlide == nMax) {
      nextBtn.style.visibility = "hidden";
    }
    else {
      nextBtn.style.visibility = "visible";
    }
  ajax.doGet('doDemo.php?nSlide='+nSlide, showSlide);
}

var showSlide = function(str) {
  document.getElementById('demoarea').innerHTML = str;
 // printResult(str);
}

function printResult(str) {
  var demoarea = document.getElementById('demoarea');
  if (demoarea.firstChild) {
    demoarea.removeChild(demoarea.firstChild);
  }
  demoarea.appendChild(document.createTextNode(str));
}

///////////////////////////////////////////////////////
///////////////////////////////////////////////////////

function getPrev(n) {
  var prevBtn = document.getElementById('prevBtn');
  var nextBtn = document.getElementById('nextBtn');
  nextBtn.style.visibility = "visible";
    if (n > 1) {
      nSlide--;
    }
  document.forms[0].nS.value = nSlide;
  getDemo(nSlide);
}

function getNext(n) {
  var prevBtn = document.getElementById('prevBtn');
  var nextBtn = document.getElementById('nextBtn');
  prevBtn.style.visibility = "visible";
    if (n < nMax) {
      nSlide++;
    }
  document.forms[0].nS.value = nSlide;
  getDemo(nSlide);
}