CrazyEgg.com – How does it track Visitor Clicks?

<script type="text/javascript">
//<![CDATA[
document.write('<script'+'
src="http://crazyegg.com/pages'+'
/scripts/4382.js?'+(new Date()).getTime()+
'" type="text/javascript"></scr'+'ipt>');
//]]>
</script>

var _cep=[];
var _ceL={};
var _ceLT=new Date();
var _ceET=null;
var _ceAID=new Array();

//creates a unique id for elements that have no id tag
function CreateUniqueID(_1)
{
    var _2=false;
    var _3="";
    for(i=0;
    i<_ceAID.length;i++)
    {
        if(_1==_ceAID[i].name)
        {
            _2=true;
            break;
        }
    }

    if(_2)
    {
        _ceAID[i].count+=1;
        count=_ceAID[i].count;
    }
    else
    {
        _ceAID.push({name:_1,count:1});
        count=1;
    }
    return (_1+count);
} 

//We wanna have a good name for all the
//elements that we have on the heatmap
//afterwards.
//An anchorElements element is either a Link 
//or an Image 
function CreateNameForElement(anchorElement)
{
    imgCollection =
    anchorElement.getElementsByTagName("img");

    //check if the object that the user clicked on is 
    //an image, if yes, we can either use the alt 
    //tag, the title or some other tags.
    if(imgCollection.length>0)
    {
        img=imgCollection[0];

        if(img.alt)
        {
            link_text=img.alt;
        }
        else
        {
            if(img.title)
            {
                link_text=img.title;
            }
            else
            {
                if(img.longDesc)
                {
                    link_text=img.longDesc;
                }
                else
                {
                    link_text=img.src;
                }
            }
        }
    }
    //if it is not an image, lets see if we can use 
    //the inner text or a title or something
    else
    {
        if(anchorElement.innerText)
        {
            link_text=anchorElement.innerText;
        }
        else
        {
            if(anchorElement.text)
            {
                link_text=anchorElement.text;
            }
            else
            {
                if(anchorElement.title)
                {
                    link_text=anchorElement.title;
                }
                else
                {
                    link_text=anchorElement.href;
                }
            }
        }
    }

    if(link_text=="")
    {
        link_text="No Text Found";
    }

    return link_text;
} 

//checks if the links points to a different site
function IsSameSite(linkHostname,
    locationHostname)
{
    same=(linkHostname.indexOf(locationHostname)>=
    || locationHostname.indexOf(linkHostname)>=0) ?
    true : false;
    return same;
} 

//for all pics on the page we set a link to
//crazyegg.com
//for links, we replace them with links to
//crazyegg.com
//QUESTION? not sure how they track html controls
//like buttons?
function PlaceLinksToCrazyEgg()
{
    var anchorElements =
           document.getElementsByTagName("a");

    for(var i=0; i<anchorElements.length; i++)
    {
        anchorElement = anchorElements.item(i);

        // QUESTION? looks like we do not replace
        //absolute links?
        if(anchorElement.href.indexOf("http")==0)
        {
            link_id="CEID_";
            link_text="";
            if(anchorElement.id=="")
            {
                link_id +=
                    IsSameSite(anchorElement.hostname,
                    location.hostname) ?
                    anchorElement.pathname :
                    nchorElement.href;
                link_id =  link_id.replace(/W/g,"_").
                link_id =  link_id.replace(/_+/g,"_");
                link_id =  link_id.replace(/_$/,"");
                link_id =  CreateUniqueID(link_id);
            }
            else
            {
                link_id = anchorElement.id;
            }

            link_text =
                CreateNameForElement(anchorElement);

            _cep.push(
            {
                "text":link_text,
                "href":anchorElement.href,
                "target":anchorElement.target,
                "id":link_id,"name":anchorElement.name
            });

            var _9="?";
            _9+="pid=83913&";
            _9+="token=124678787&";
            _9+="text="+escape(link_text)+"&";
            _9+="href="+escape(_7[i].href)+"&";
            _9+="element_id="+escape(link_id);
            anchorElement.oldHref=
                anchorElement.href;
            anchorElement.href=
                 "http://crazyegg.com/track/"+_9;
            FixStatusBar(anchorElement);
        }
    }
} 

//this way the status bar still shows the old url and 
//not to crazyegg.com
function FixStatusBar(_a)
{
    var _b=_a.onmouseover;

    if(typeof _a.onmouseover!="function")
    {
        _a.onmouseover=ShowLinkInStatusBar;
    }
} 

function ShowLinkInStatusBar()
{
    window.status=this.oldHref;
    this.onmouseout=function()
    {
        window.status="";
        return true;
    } 

    return true;
} 

// QUESTION? No idea what this does 
function ceHC(_c)
{
    var _d="";
    _d+="pid=83913&";
    _d+="token=124678787&";
    _d+="text="+_ceL.text+"&";
    _d+="href="+escape(_ceL.href);
} 

// QUESTION? No idea what this does 
function ceMoveOn()
{
    switch(_ceL.target)
    {
        case "": self.location=_ceL.href;
        break;

        case "_new": ceNewWindow=
            window.open(_ceL.href);
        break;

        case "_blank": ceNewWindow=
            window.open(_ceL.href);
        break;
    }
} 

PlaceLinksToCrazyEgg();