How to create a tracking script with js and php?

Question

I want to create a simple tracking script to give to my clients. Something similar with GA but very basic.

The requirements are

give the clients a single and simple js script like google Analytics does

make most of the logic inside the js file loaded by 3th party sites from the main site

collect in PHP the information and store it

What I can't figure yet is what are the ways to do this? Google from what I see is loading a gif file, stores the information and parses the logs. If I do something similar sending the data to a php file Ajax cross site policy will stop me, from what I remember.

So what is a clean way to do this ? ( I don't need code just the logic behind it )

Answer 1

Method a - web bug:

Give the user this:
<img src="http://www.yourserver.com/yourtracking.php?associateid=3rdpartyid" width="1" height="1" />

have the php return header("content-type:image/gif"); and serve them a gif file for their effort.

Method b - script

Create a php file that can parse parameters and have it return content-type:text/javascript Have them load it like this: <script type="text/javascript" src="http://www.yourserver.com/yourtracking.php?associateid=3rdpartyid"></script>

If you want to you can do additional stuff like

<script type="text/javascript">
  var associateId = "12345";
  var trackingPage="homepage";
</script>
<script type="text/javascript" src="http://www.yourserver.com/yourtracking.php?associateid=3rdpartyid"></script>

then in the php have code like this (watch the nested quotes)

$str = 'var url = "http://www.yourserver.com/moretracking.php?associateid="+associateId+';
$str .= '"&page="+trackingPage+"&ref="+escape(document.referrer);\n';
$str .= 'document.write(\'<img src="\'+url+\'"/>\');';

echo $str;