Is it possible to compare two objects only between the keys / properties they both share?

So I have two objects

address: {
  id: 1234,
  city: "foo",
  country: "bar",
  name: "baz"
}

and

defaultAddress: { 
  id: 1234,
  city: "foo",
  country: "bar",
  firstName: "ba",
  lastName: "z"
}

If I try to do a straight up comparison / assertion between them, i.e.

expect(address).to.contain(defaultAddress)

(or the other way around), it'll fail because each contains fields the other does not

(AssertionError: expect {address} to have a property 'firstName')

I only want to comparing the values in the keys they both share. Is it possible to do something like that programmatically?

You're trying to match the objects on the subset of shared keys. This can be done as follows.

for(const key in address) {
  if(typeof defaultAddress[key] !== 'undefined') {
    expect(address[key]).to.equal(defaultAddress[key])
  }
}

Also have a look at this answer.