Need to see if "referrer" is inside/outside my site

I need to find out if someone has accessed my site's main page from outside my entire site or from a page within my site. What's the most straightforward way to do this? Should I just see if my domain's URL is found in the document.referrer property?

if (document.referrer&&document.referrer!="")
{
if (document.referrer.indexOf("https://www.mydomain.com")>=0)
{
...visitor came from within my site...
}
else
{
...visitor came from outside my site...
}
}

How does that look?...0 being the first position in the string. And can someone tell exactly why the line (document.referrer&&document.referrer!="") is always used when this property is referred to? Wouldn't document.referrer!="" suffice? Does it translate in English to "not null AND not empty" or something?

UPDATE TO POST: I started by putting code on a page to display the document.referrer. When I key it into my Yahoo Store Editor it works perfectly displaying actual web URLS of the editor itself. When I "publish" the page on the net, the page just gives me nothing but a "blank page". It's like the document.referrer property is always null. Currently stumped.

The referrer property is being sent by less and less internet browsers. This is because some people see it as an invasion of privacy and also because of the fact that firewallsare more common.

I had a feeling that might be the case. I also realized that my approach was flawed because alot of people don't come to my site through my main page anyway - which would short-circuit my algorithm. I'll come up with another idea. Thanks.