Chai: deepEqual may ignore object's null/undefined properties, by configuration

[jpnovais]

I think it would be nice to have a chai configuration property to set chai to ignore null or undefined properties on object deepEqual assertion (e.g. chai.config.ignoreNullOrUndefinedProperties = true).

    var objA = {
        foo: 'bar',
        not_relevant: undefined,
        not_serializable: null
    };

    expect(objA).to.eql({foo: 'bar'});
    // false

    expect(JSON.pase(JSON.stringify(objA)).to.eql({foo: 'bar'}));
    // true

This is useful for instance when we want to filter objects's properties before serialization (e.g REST APIs). These objects may have optional properties set to undefined which won't be serialized. Example:

  var pick = require('mout/object/pick');
  var USER_FILTER = ['login','company'];

  function filterUser(user) {
    if(!user) return;

    return {
      login: user.login,
      company: user.company,
    };
    // same as: return pick(user, USER_FILTER);
  };

  var usersBD = {
    bob: {
      login: 'bob',
      lastLoggin: '2014-12-27T00:00:00+00:00',
      password: 'some_hash',
    },
    alice: {
      login: 'alice',
      lastLoggin: '2014-12-27T00:00:00+00:00',
      password: 'some_hash',
      company: 'Wonderland'
    }
  };

  //
  //
  expect(filterUser(usersBD['bob'])).to.eql({login: 'bob'});
  // will fail because filterUser(usersBD['bob']) returns
  // {login: 'bob', company: 'udefined'}
  // but since the object will be  serialized to JSON
  // does not matter

  expect(filterUser(usersBD['alice'])).to.eql({
    login: 'alice',
    company: 'Wonderland'
  }); // success

For this simple case scenario, I cloud do something like:

function filterUser(user) {
  if (!user) return;

  var filteredUser = {
    login: user.login
  };

  if (user.company) {
    filteredUser.company = user.company;
  }

  return filteredUser;
};

But sometimes we have several optional properties which will require more verbose code polluted with if statements.

Currently I overcome this with JSON.stringify.

Is this a good feature, does it meet chai purpose?

[keithamus]

Sorry for late reply @jpnovais. Thanks for the issue! I'd like to learn a little bit more about the use case before we go forward with implementing code.

I'd argue that the test should be as strict as possible, and in fact filterUser is always returning company, whether or not it is defined. That is the contract set by your filterUser method - seemingly intentionally (because of the explicit return). Perhaps, if I may suggest, you need to rethink your testing strategy. You mention that "since the object will be serialized to JSON does not matter" - I would suggest that and say that your tests need to be higher level then.

I don't speak for the community, so if there is a strong support for this then I believe we should implement it, but I'd personally like to see a stronger use case because I think the current behaviour is correct.

Now, if we were to go down the road of implementing some kind of flag to disregard undefined values, I'd recommend it become a property - perhaps something like expect(foo).to.loose.eql()? chai.config is ideally meant for global config while this (to me) sits firmly in the camp of changing assertion behaviours.

[dclucas]

Found this issue when I was looking for a way to easily implement a test for a REST API. We are writing a JSONAPI compliant API. For POST actions, the specs say that the server should generate the IDs in case none are provided.

So, a request such as this

POST /photos
Content-Type: application/vnd.api+json
Accept: application/vnd.api+json

{
  "photos": {
    "title": "Ember Hamster",
    "src": "http://example.com/images/productivity.png"
  }
}

Should yield a response like this:

HTTP/1.1 201 Created
Location: http://example.com/photos/550e8400-e29b-41d4-a716-446655440000
Content-Type: application/vnd.api+json

{
  "photos": {
    "id": "550e8400-e29b-41d4-a716-446655440000",
    "title": "Ember Hamster",
    "src": "http://example.com/images/productivity.png"
  }
}

The ideal solution for us (of course, unless there's a better idea around) would be to perform a comparison that ignores the id of the request JSON object when comparing to the response.

And I agree that modifying global behavior would be less the ideal. For example, the same specs say that when posting with a client-generated ID, it should be stored as-is, so we would not be able to globally ignore an attribute.

[ahamid]

if this were available it may be possible to work around #304

[keithamus]

Having a re-read of this, it seems like this is more like https://github.com/chaijs/chai/issues/72 right? It seems like what @jpnovais and @dclucas would get most benefit from is a .properties like assertion, or similar, where you only want to assert on a subset of an object, e.g.

expect({ a: 1, b: 2, c: 3 }).to.have.subset({ a: 1 });

Thoughts?

[jpnovais]

expect({ a: 1, b: 2, c: 3 }).to.have.subset({ a: 1 }); seems to work for @dclucas. In my case what I need is something like:

expect({ a: 1, b: 2, c: 3 }).to.loose.eql({ a: 1, b: 2 }); 
// FAIL - property c is not expected

expect({ a: 1, b: 2, c: undefined }).to.loose.eql({ a: 1, b: 2 });
// PASS - property c is undefined so it's ignored

expect({ a: 1, b: 2, c: null }).to.loose.eql({ a: 1, b: 2 });
// FAIL/PASS? - property c is null. should null properties be ignored as well?

Is it useful (makes sense) to have a property like this?

[evtaranov]

+1
I have a similar case to test, where i need to ignore undefined values, because after JSON.parse(JSON.toString(...)) they are lost and deepEqual() return false.

[lucasfcosta]

Hello guys, thanks for your feedback! :smile:

We currently have this, I think it could help you solve a big part of this problem. I think it would be easy to design a workaround using it. Maybe you could write something like:

var obj = { a: 1, b: 2, c: undefined, d: null };
var subset = {};
for (let key of Object.keys(obj)) {
  if (obj[key] !== null && obj[key] !== undefined) {
    subset[key] = obj[key];
  }
}

expect(obj).to.include.subset(subset);

I'm not sure this use case is common enough for us to have a specific assertion for this, maybe a flag would be enough, but even then it would be easy to design a workaround and maybe some people would like to ignore just undefined or just null so we would have to adapt to these cases. Just wrapping the code I wrote above into a function would be enough if you don't want to apply this recursively (on nested properties). Anyway, I'd like to hear further opinions so everyone gets satisfied. What do you guys think about this?

[gregglind]

Once nesting and recursion become involved, the semantics for 'ignore undefined' becomes more complicated. For top-level key stuff, include.subset seems to be sufficient here.

As an alt. proposal... maybe having a utility function that does the 'subsetting' could be useful? Turning @lucasfcosta 's code above into a (js5!) function, for example. chai.utils.stripObject?

[lucasfcosta]

Hi @gregglind, thanks for sharing your opinion!
Lodash already has this, it even allows the user to specify a criteria to define which things should be excluded.

If you are interested in it you can take a look at _.pickBy().

[keithamus]

Thanks everyone for your feedback on this issue.

We've got a plan for this in our Roadmap https://github.com/chaijs/chai/projects/2! It'll likely be different to what @jpnovais proposed, but rest assured this is something we'll have a good way of handling come chai 5. We'll be releasing chai 5 soon, but for now I'll close this issue because it is tracked on our roadmap.

[ronjouch]

"We've got a plan for this in our Roadmap https://github.com/chaijs/chai/projects/2 ! It'll likely be different to what jpnovais proposed, but rest assured this is something we'll have a good way of handling come chai 5. We'll be releasing chai 5 soon, but for now I'll close this issue because it is tracked on our roadmap."

Hi @keithamus . The roadmap is a moving artifact, and I think it no longer references what it did at the time you wrote that. Can you name / precise / link to the precise feature of chai 5 you were talking about? Thanks 🙂.

[keithamus]

Sure @ronjouch! Specifically https://github.com/chaijs/chai/projects/2#card-10444381 and https://github.com/chaijs/chai/projects/2#card-10444260 capture the desired functionality. This is a matcher API which would allow you to pass expectations as properties in a deep-eql assertion, e.g.

expect({ a: 1, b: 2, c: 3 }).to.deep.eql({ a: 1, b: 2, c: expect.to.be.a('number')  }); 

or in the case of the OPs example for a users table you could do something like:

  expect(usersBD['alice']).to.eql({
    login: 'alice',
    password: expect.to.be.a('string').with.lengthOf(40),
    lastLogin: expect.to.be.a('string'),
    company: 'Wonderland'
  }); // success

If you're looking for an assertion which only tests the existance of some keys, we already have this available. But we think having a matcher API to make more broad assertions on object properties is the right direction here.