function incOff(id){
    var url = 'ajax.php?act=1&id=' + id;
    var ajax = new createRequestObject(url, offerQuantityResponse);
    ajax.doGet();
}
function decOff(id){
    var url = 'ajax.php?act=2&id=' + id;
    var ajax = new createRequestObject(url, offerQuantityResponse);
    ajax.doGet();
}
function incAcc(id){
    var url = 'ajax.php?act=3&id=' + id;
    var ajax = new createRequestObject(url, accQuantityResponse);
    ajax.doGet();
}
function decAcc(id){
    var url = 'ajax.php?act=4&id=' + id;
    var ajax = new createRequestObject(url, accQuantityResponse);
    ajax.doGet();
}
function offerQuantityResponse(responseXML) {
   var msg = responseXML.getElementsByTagName("msg")[0].firstChild.nodeValue;
   if(msg!='Error') {
        var response = msg.split(",");
        document.getElementById("oq_"+response[0]).innerHTML = response[1];
   }
   else alert(msg);
}
function accQuantityResponse(responseXML) {
   var msg = responseXML.getElementsByTagName("msg")[0].firstChild.nodeValue;
   if(msg!='Error') {
        var response = msg.split(",");
        document.getElementById('aq_'+response[0]).innerHTML = response[1];
   }
}

function createRequestObject(url, callback) {

    var req = init();
    req.onreadystatechange = processRequest;

    function init() {
      if (window.XMLHttpRequest) {
        return new XMLHttpRequest();
      } else if (window.ActiveXObject) {
        return new ActiveXObject("Microsoft.XMLHTTP");
      }
      return false;
    }

    function processRequest () {
      if (req.readyState == 4) { // readyState of 4 signifies request is complete
        if (req.status == 200) { // status of 200 signifies sucessful HTTP call
          if (callback) callback(req.responseXML);
        }
      }
    }

    this.doGet = function() {
      req.open("GET", url, true);
      req.send(null);
    }
}