What parameters are passed to Mongoose callbacks

Question

In the mongoose documentation it frequently lists an optional callback for certain query operators (like findOneAndUpdate), however, it does not mention what parameters (arguments) the callback takes. What are they, and how would I find out?

Also, if conditions, update etc. are optional, and I want to specify a callback at the end, do I have to pass in the null value, or empty objects or can I just specify the callback -- and hose does Mongoose know?

Model.findOneAndUpdate([conditions], [update], [options], [callback])

Answer 1

For nearly all mongoose queries the provided callback function will be called with two arguments in the node callback pattern callback(err, results) as stated in the documentation:

Anywhere a callback is passed to a query in Mongoose, the callback follows the pattern callback(error, results). What results is depends on the operation: For findOne() it is a potentially-null single document, find() a list of documents, count() the number of documents, update() the number of documents affected, etc. The API docs for Models provide more detail on what is passed to the callbacks.