How to obtain a MongoDb collection in NodeJS

How to obtain a MongoDb collection in NodeJS

There are two different methods to obtain a reference to a MongoDB
collection - both of them are used throughout the official documentation.
There is
var mycollection = db.collection('mycollection)'
and there is
db.collection('mycollection', function(err, collection){
//use collection
}
I tend to use the second one because it is consistent with
"db.createCollecion(collection, callback)"
What is the difference between these methods?
Is there any database interaction when using these methods?