Just use the .replace function to remove the url tags.
Code:
<script>
var testurl='[u#rl]hello.com[/u#rl]';
testurl = testurl.replace(/\[u#rl\]/g,'');
testurl = testurl.replace(/\[\/u#rl\]/g,'');
document.write(testurl);
</script>
Note, remove the #s from the code. I have to insert them because I have less than 5 posts, so can't post a url tag (even in code!).
Cheers.