callback function gets called twice

[romsok]

So I am getting some data via AJAX, from a Java servlet on the server side.

I had some alert boxes set up, and the request gets submitted only once.
But, the callBack function in the onreadystatechange iterates through the states twice - reaches state == 4 , status == 200, does its work, and then goes through the states again... I have no idea why this is happening?

Here is the code:

function createRequest()
{
	try
	{
		request = new XMLHttpRequest();
	}
	catch(tryMS)
	{
		try
		{
			request = new ActiveXObject("Msxml2.XMLHTTP");
		}
		catch(otherMS)
		{
			try
			{
				request = new ActiveXObject("Microsoft.XMLHTTP");
			}
			catch(failed)
			{
				request = null;
			}
		}
	}
	
	return request;
}

function getSubmitRequest()
{

	//Create request object
	req1 = createRequest();
	
	if(req1 == null)
	{
		alert("Unable to create request");
		return;
	}
	
	//Configure request object
	var url = "/ajaxurl";
	
	req1.open("POST",url,true);
	
	//Tell the request object what to do when server responds -assign a call-back function
	req1.onreadystatechange = populatePage;
	
	//Make the request
	req1.send(null);

}

function populatePage()
{

	
	if(req1.readyState == 4)
	{
		if(req1.status == 200)
		{			
			var responseDoc = req1.responseXML;
			populatePageParts(responseDoc);
		}
	}
}

[omnicity]

I can't see anything wrong with the bits you have given us, but clearly this is an extract of the whole page, so maybe the fault lies elsewhere?
Have you tried debugging this - first thing I would want to know is if the function is being called twice, or if it is looping somehow, and to double-check whether the callback was somehow getting registered twice.

[romsok]

This stopped happening after I removed some alert boxes.

[omnicity]

If I am working on anything significant, I usually set up a DIV that I can use as a logging console - there is almost nothing that is as frustrating as putting an alert within an onfocus method (or something similar) and having it loop endlessly as a result...