Using should.js how can I test for an empty object?

user1Stats.should.be.instanceof(Object);
(user1Stats).should.have.keys();

I get the following error:

Error: keys required
    at Object.Assertion.keys

The instanceof(Object) works, but I want to make sure there is no data in it.

user1Stats.should.be.an.Object;
user1Stats.should.be.empty;

of using .and to chain both asserts:

user1Stats.should.be.an.Object.and.be.empty;

P.S. By the way, your code also looks fine.