function markdate(el, year, month, day, id) {
  if (el.style.border == 'rgb(255,0,0) 1px solid' || el.style.border == '1px solid rgb(255, 0, 0)') {
    el.style.border = 'rgb(255,255,255) 1px solid';
    ajax("product_session.php?set=0&year=" + year + "&month=" + month + "&day=" + day + "&id=" + id);
  } else {
    el.style.border = 'rgb(255,0,0) 1px solid';
    ajax("product_session.php?set=1&year=" + year + "&month=" + month + "&day=" + day + "&id=" + id);
  }
}

function GetXmlHttpObject(handler) {
  var objXMLHttp = null;
  if (window.XMLHttpRequest) {
    objXMLHttp = new XMLHttpRequest();
  } else if (window.ActiveXObject) {
    objXMLHttp = new ActiveXObject("Microsoft.XMLHTTP");
  }
  return objXMLHttp;
}

function ajax(url, element) {
  xmlHttp = GetXmlHttpObject();
  if (xmlHttp == null) {
    alert("Browser does not support HTTP Request");
    return;
  }

  url = url + "&sid=" + Math.random();

  if (element) {
    xmlHttp.onreadystatechange = element;
  }

  xmlHttp.open("GET", url, true);
  xmlHttp.send(null);
}