Add sparseEql functionality

[apadmarao]

{foo: undefined}.should.eql({}); // throws AssertionError

Would you support a PR to add a function sparseEql that passes in this case?

This function can be implemented by modifying the cheap equality tests in objEquiv (lib/eql.js). We could filter keys with undefined value, then afterwards check that both objects have the same number of owned properties and do the cheap key test.

[btd]

Nope, eql.js should just check equality and nothing more. Could you describe your use case? For me it looks like you need to use .containEql instead of .eql, but i don't know your case.

[apadmarao]

I often write code like:

function sillyObject(foo, bar) {
  return {
    foo: foo, 
    bar: bar
  };
}

sillyObject('foo', undefined).should.eql({foo: 'foo', bar: undefined})

I would like to have an equality operator that will disregard owned keys, if their value is undefined. This will allow me to write cleaner tests, like:

sillyObject('foo', undefined).should.eql({foo: 'foo'})

I am writing server-side Javascript, and stringify my objects into JSON before sending them to the client, so keys with value undefined are filtered. I do not believe .containEql will work in this case.

[btd]

Why do not use .contactEql there?

sillyObject('foo', undefined).should.containEql({foo: 'foo'})

[apadmarao]

I think .containEql will pass in cases where it should not. I want a method that disregards only keys with value undefined.

{foo: 'foo', bar: undefined}.should.containEql({}) // does not throw, but should 

[btd]

Well, every object contains {} as subobject. Ok, agree there is nothing in should for this. Not sure that it is quite usefull, so PR welcome (only pls just filter properties, do not touch eql.js).

[btd]

Close this one as it does not look useful, if anyone want to make PR for this, you will can always reopen, this. Closed for me means that i will not add this myself.