Hi Guys, 
I would like to create a custom button with Content Source as URL. 
Is there a way we can can dynamic url i.e. with IF in the url? 
example
/a06/e?CF00N2700000behac={!Contact.Last_Name}&IF(Field='a value', RecordType=012O00000006Fiaa , RecordType=012O00000006Fibb)?

If not, can you please give me an example in Java Script

Thanks,