@nemtsov PR updated.

ping @nemtsov

Apologies for the delay; I haven't had much time to thoroughly review this last week.

There are two changes in this PR. The bug-fix ("if not array -> _properties" one) I completely agree with and am ready to merge and the "if plain object -> {}" one, which needs more work. So, if you extract the former into a separate PR, I'll merge it ASAP.

Regarding the latter, there are two issues I see with it:

1. It's inconsistent with other test-cases
   • Why is mask({a: 3}, 'b') null and not {} if we're making mask({a: {b: 3}}, 'a/c'), {}?
   • Why is mask({a: [{b: 3}]}, 'a/c') null and not {a: []} or even worse {a: [{}]}(??) ?
   • Assuming function A() { this.a = 3; this.b = 4}; var a = new A(), why does: mask(a, 'b'); return {b: 4} but mask({a: a}, 'a/c'); returns null, while mask({a: a}, 'a/b'); returns {a: {b: 4}}?
2. The implementation of object detection does not work for the following case:

• mask({a: {constructor: 2}}, 'a/c') -> null

@nemtsov PR submitted here. I'll take a look at your points and get back to you.

@fixe I merged your other PR. Thanks!

@nemtsov I added another commit to this PR.

I had to change the .travis.yml to use iojs instead of nodejs due to the added support of the assert.deepStrictEqual() (See nodejs/node#639).

This was done because assert.deepEqual({}, []) was considered valid when it's not really what we intended.

Also, in regard to your previous questions:

Why is mask({a: 3}, 'b') null and not {} if we're making mask({a: {b: 3}}, 'a/c'), {}?

Absolutely correct. Fixed by the latest commit.

Why is mask({a: [{b: 3}]}, 'a/c') null and not {a: []} or even worse {a: [{}]}(??) ?

In my opinion, {a: [{}]} is correct in that case. The user supplied an array with an object inside. That object simply did not have any matching masks and so we were left with an empty object.

Assuming function A() { this.a = 3; this.b = 4}; var a = new A(), why does: mask(a, 'b'); return {b: 4} but mask({a: a}, 'a/c'); returns null, while mask({a: a}, 'a/b'); returns {a: {b: 4}}

Fixed by the latest commit.

ping @nemtsov

Totally lost track of this PR. Will review / merge or comment on it this week.

ping @nemtsov

Needed this PR again today. Here's what I was doing:

const data = {
  user: {
    lastName: 'foo'
  }
};

mask(data, 'user(firstName)');

The above mask was returning {} when it should really be returning { user: {} }, which this PR correctly fixes.

@nemtsov any chance you could take a look at this?

Just wanted to let you know that I haven't forgotten about this and want to merge it in. I'll respond with specific comments as soon as I have some time.

@nemtsov any chance of merging this one?

Merged. Thank you for your contribution and patience.