Javascript / jQuery back button - so long as last page was part of current site?

Question

With the code below I can make a 'back' button, but is there a way of making the link require that the last page was part of the current site?

$(document).ready(function(){
    $('a.back').click(function(){
        parent.history.back();
        return false;
    });
});

If the last page wasn't part of the current site then ideally id like to be able to specify a backup link.

Thanks

Answer 1

How about using document.referrer?

$(document).ready(function(){
    $('a.back').click(function(){
        if(document.referrer.indexOf(window.location.hostname) != -1){
            parent.history.back();
            return false;
        }
    });
});