How can I determine if the document.referrer is from my own site?

Originally posted at JavaScript - Am I the Referrer?

When someone comes to our website for the first time, we store the referrer in a cookie. This way, if they download our demo, we can get the original referrer from the cookie and we learn what sites are effective in driving leads to us.

Of course, every subsequent page a visitor hits on our website will show the referrer as our website. We don't want those. What we first did to avoid this was look for the text "windward" in the referrer and if so, assume that was from our site. The problem with this is we found a lot of referrer urls now have windward in them, either as a search term or part of a url that talks about Windward. (This is good news, it means we are now a well known product.)

So that brought me to our most recent approach. This should work for any site and should only reject referrers from the same site.

function IsReferredFromMe()
{

    var ref = document.referrer;
    if ((ref == null) || (ref.length == 0)) {
        return false;
    }
    if (ref.indexOf("http://") == 0) {
        ref = ref.substring(7);
    }
    ref = ref.toLowerCase();

    var myDomain = document.domain;
    if ((myDomain == null) || (myDomain.length == 0)) {
        return false;
    }
    if (myDomain.indexOf("http://") == 0) {
        myDomain = myDomain.substring(7);
    }
    myDomain = myDomain.toLowerCase();

    return ref.indexOf(myDomain) == 0;
}

document.referrer.indexOf(location.protocol + "//" + location.host) === 0;