$ /m/3.1.6/bin/mongo --norc
MongoDB shell version: 3.1.6
connecting to: test
> print(db.serverStatus())
[object Object]
>
bye
$ /m/3.1.7/bin/mongo --norc
MongoDB shell version: 3.1.7
connecting to: test
> print(db.serverStatus())
[object BSON]
> BSON
2015-10-14T23:51:54.075+1100 E QUERY    [thread1] ReferenceError: BSON is not defined :
@(shell):1:1

> Object
function Object() {
    [native code]
}
> var a = db.serverStatus()
> a instanceof BSON
2015-10-14T23:52:16.730+1100 E QUERY    [thread1] ReferenceError: BSON is not defined :
@(shell):1:1

> a instanceof Object
true
> a.pid instanceof NumberLong
true
> a.pid instanceof Object
true