isEmpty check for lenght === 0 in any object with lenght property

[marioizquierdo]

Apply some duck typing ruby-style checks, and now isEmpty behavior is more intuitive.

Now you can do things like this (that is not true with the current implementation):

matched_elements = jQuery(selector);
if (!_.isEmpty(matched_elements)) {
  do_stuff();
}

In general, makes sense to think that anything with length === 0 is empty.

[michaelficarra]

If the length property is enumerable, it's not empty. From the comment just a few lines up,

An "empty" object has no enumerable own-properties.

This function deals with objects and their properties, not arrays or array-like objects and their members.

[marioizquierdo]

Just for curiosity, it would be nice to have a broken test, or at least an example here as where checking for length === 0 is not OK.
Thanks

[jdalton]

@michaelficarra

This function deals with objects and their properties, not arrays or array-like objects and their members.

See line 830. The isEmpty method deals with arrays and strings, so practically array-like values :P

[marioizquierdo]

@michaelficarra, @jashkenas

I guess the point here is this:

Underscore current version:

_.isEmpty({length: 0}); //=> false
_.isEmpty({length: null}); //=> false
_.isEmpty({foo: bar, length: 0}); //=> false

Pull request 690 (after this pull request):

_.isEmpty({length: 0}); //=> TRUE
_.isEmpty({length: null}); //=> false
_.isEmpty({foo: bar, length: 0}); //=> TRUE

This is not covered in the test suite.
If we clearly decide something, I am happy to add a test case for this, to avoid future "flaws" and document better the expected behavior of the isEmpty method.

[braddunbar]

FWIW, this patch would break the usage of isEmpty in Backbone.

_.isEmpty({}); // -> true
_.isEmpty({length: 0}); // -> false