Objects with a length property of 0 evaluate to false in handlebars conditionals

[kevinkucharczyk]

When using the if template conditional on objects that have a length property equal to 0 the conditonal evalutes to false and will not render what was expected.

Here's a twiddle with an example: https://ember-twiddle.com/7434ede64e1ed3888b2d

An object with length greater than 0 will evaluate to true and render properly.

I believe such objects might be treated as arrays, leading to this issue.

[pixelhandler]

@kevinkucharczyk This looks like a bug, seems that the check for length == 0 should only be done for an array. An object with a property of length that equals 0 should not be false, as in your example:

{
  title: 'Test Track 1',
  artist: 'Test Artist 1',
  length: 0
}

This object is should not be treated as falsy.

[stefanpenner]

The relevant code:

1. https://github.com/emberjs/ember.js/blob/master/packages/ember-views/lib/streams/should_display.js#L66-L67
2. https://github.com/emberjs/ember.js/blob/master/packages/ember-runtime/lib/utils.js#L51

[stefanpenner]

related issue: #12688

[tragiclifestories]

Digging around in lodash.isArray, I see they have a much more heavily qualified check against the length property - basically, not only that it exists, but that it is a non-negative integer.

On the other hand, I would guess that a length property on some arbitrary object would be fairly likely to be a positive integer, so I'm not sure that would be perfectly satisfactory.

EDIT: it also checks that Object.prototype.toString.call(foo) === '[object Array]', on closer examination, which may settle things.

[locks]

I believe this is fixed by the related PRs.