Mongoose using $slice, not for query

I wanted to know if its possible to use $slice without the $each in mongoose. I'm trying to push to an array of songs but when it reaches a point of 10 songs, for the array to slice the old songs out of the array. Is this even possible and if not is there a trick to performing this action?

Code I have so far but it isn't slicing anything:

Playlist.findByIdAndUpdate(playlist._id,
            { $push:{ "songs" : song, $slice: -2 }},
            { safe: true, upsert: true },
            function( err, model ) {
              cb(err, model);
            }
          );