Hi I have this link

Code:
http://www.facebook.com/sharer.php?u=
I want to append the current url to it and make thw whole thing a link. I've got the below code which is almost working I'm just not sure of how to append the link to the window.location part. ANy help would be great. Thanks

BELOW CODE NOT WORKING

Code:
 document.getElementById("facebook").href = "http://www.facebook.com/sharer.php?u=".window.location.toString();