Ember.isArray will not detect plain object with length property

[tragiclifestories]

To fix #12738 and #12688

This is a backwards incompatible change (if someone was relying on this test returning true for an object that happened to have a length property), but the old behaviour is surprising and out of line with native Array.isArray implementations, lodash.isArray and so on.

[cibernox]

I'd say that this is not desired behaviour. An object having a length property is not enough to be considered an array-like object.

Neither Array.isArray({ length: 1 }) not _.isArray({ length: 1 }) return true.

[tragiclifestories]

@cibernox That is what this change is supposed to achieve; the current behaviour of isArray will pass for {length: 1}.

[cibernox]

Oh, I understood it the other way around. My bad. In that case seems reasoable, but a breaking change in such a basic method is delicate.

[cibernox]

Id say that an aray-like object should be any object where typeof [Symbol.iterator] === function, but I guess that this is not cross-browser yet.

[tragiclifestories]

Indeed. I wouldn't have worked on it if the mood music in the issues linked hadn't been of a 'hell with it, go ahead' kind of tone. And yes, it would have been nice to have a Ruby/Python style iterable interface like 10 years ago, but we are where we are ... :-)

[tamzinblake]

We just spotted this rather unexpected behavior - is there any movement on this PR?

[tragiclifestories]

@thomblake tbh I'd almost forgotten about it myself.

[mixonic]

I'm closing this in favor of the approach taken by #12708. That seems to handle the root cause error, that fileList is considered an object, a bit better. Please let me know if I might be missing something though. Thanks!

[tragiclifestories]

@mixonic Well, I still think this is unexpected behaviour. Eg, say I have a Product class, which has separate size properties for depth, width and length. I would not want ember to assume that instances of this class were iterable.

[tamzinblake]

Yeah we also encountered this in a different context and it was really surprising.