Chai: lengthOf doesn't work with objects

[jockster]

assert.lengthOf {error: "Error", status: false}, 2 # => expected { Object (status, error) } to have a property 'length'

My workaround:

 assert.equal Object.keys(myObj).length, 2

What about implementing something like above inside the lengthOf() that is used on objects to get the number of top-level properties?

Perhaps something more robust is needed, http://stackoverflow.com/questions/5223/length-of-javascript-object-ie-associative-array

[domenic]

First, it's a bit disrespectful to post bug reports in a language other than the one the project is written in. It'd be cool if you could rewrite your bug report for ChaiJS in... JS.

That said, I think this is error-prone and not very transparent. Objects don't have a canonical "length." E.g. what is the length of { length: 9001 }. You are actually asking what the length of the object's keys array is, and that would be done exactly as you describe:

assert.equal(Object.keys(myObj).length, 2);

[jockster]

Sorry. Didn't thought that two lines of coffee would offend, but here we go:

Problem:

assert.lengthOf({
  error: "Error",
  status: false
}, 2); //  => expected { Object (status, error) } to have a property 'length'   

Eventual solution:

assert.equal(Object.keys(myObj).length, 2); 

I am well aware of the fact that objects doesn't have a "length" per se. I think most of us are.

However it is helpful, at least to me, to be able to get number of top-level props from an object easily. What do you think?

[domenic]

Well, I repeat my earlier question. What do you expect for the following cases:

var obj = { length: 9001 };

var notAnArray = document.querySelectorAll("div");
notAnArray.length = 100;

var hasNoOwnProperties = Object.create([1, 2, 3]);

However it is helpful, at least to me, to be able to get number of top-level props from an object easily. What do you think?

Personally, I think the code is a lot clearer for anyone reading it if you use the normal JavaScript way of getting the number of top-level properties of an object: Object.keys(obj).length. Otherwise, when reading the tests, you have to ask yourself which particular flavor of magic length-determination is used by Chai.

We'll see what @logicalparadox thinks though!

[logicalparadox]

Changing the way lengthOf behaves to your suggestion adds a level of ambiguity that I am not comfortable with. I think many (myself especially) rely on lengthOf to throw if there is not a length property on whatever object or array I happen to be testing. I also find the Object.keys(obj).length solution much more descriptive than anything I can think of for core.

If you do this a lot and really want a method on the assert, Chai is extensible via helpers. Maybe add assert.objSize for your modules tests?