MongoDB, Mongoose - what is the best way for adding non-persistent data field to the schema?

I have Mongoose schema and I need to add a non-persistent field to it. The point of this field is to store some status, related to persistent data fields, but without need to store it to the database. I see that some Mongoose alternatives provide such a feature e.g. https://github.com/simpleviewinc/mongolayer#modeladdfieldargs, however I am not able to find similar one inside Mongoose.

Any tip would be greatly appreciated!