Add underscore and encode uri components before ajaxing them. then decode on the server.
The request module uses encodeURIComponent already for query strings and the form parameter, so that has been removed.

However, when trying to remove a track with a special character, Lastfm responds with "Invalid method signature supplied". I assume it's because the parameters which are concatenated for the api signature are not encoded. When I encode them though, I still get the same error!