var xmlHttp = createXmlHttpRequestObject(); 

function createXmlHttpRequestObject(){	
  var xmlHttp;
  // if running Internet Explorer
  if(window.ActiveXObject){
    try{
      xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
    }
    catch (e){
      xmlHttp = false;
    }
  }
  // if running Mozilla or other browsers
  else{
    try{
      xmlHttp = new XMLHttpRequest();
    }
    catch (e){
      xmlHttp = false;
    }
  }
  // return the created object or display an error message
  if (!xmlHttp)
    alert("Error creating the XMLHttpRequest object.");
  else 
    return xmlHttp;
}


function addMyDDW(i){
  // proceed only if the xmlHttp object isn't busy
  if (xmlHttp.readyState == 4 || xmlHttp.readyState == 0){
    // execute php page from the server
    xmlHttp.open("GET", "myddw.php?addMyddw=" + i, true);  
    // define the method to handle server responses
    xmlHttp.onreadystatechange = handleServerResponse;
    // make the server request
    xmlHttp.send(null);
  }
  else
    // if the connection is busy, try again after one second  
    setTimeout('addMyDDW(i)', 1000);
}


function delMyDDW(i){ 
  // proceed only if the xmlHttp object isn't busy
  if (xmlHttp.readyState == 4 || xmlHttp.readyState == 0){
    // execute php page from the server
    xmlHttp.open("GET", "myddw.php?delMyddw=" + i, true);  
    // define the method to handle server responses
    xmlHttp.onreadystatechange = handleServerResponse;
    // make the server request
    xmlHttp.send(null);
  }
  else
    // if the connection is busy, try again after one second  
    setTimeout('delMyDDW(i)', 1000);
}


// executed automatically when a message is received from the server
function handleServerResponse(){
  // move forward only if the transaction has completed
  if (xmlHttp.readyState == 4){
    // status of 200 indicates the transaction completed successfully
    if (xmlHttp.status == 200){
      // extract the XML retrieved from the server
      xmlResponse = xmlHttp.responseXML;
      // obtain the document element (the root element) of the XML structure
      xmlDocumentElement = xmlResponse.documentElement;
      // get the text message, which is in the first child of
      // the the document element
      myddwResponse = xmlDocumentElement.firstChild.data;
      // update the client display using the data received from the server
      document.getElementById("MyDdwContent").innerHTML = myddwResponse;
    } 
    // a HTTP status different than 200 signals an error
    else{
      alert("There was a problem accessing the server: " + xmlHttp.statusText);
    }
  }
}