Bluebird.props for empty Map returns an Object

[alanhoff]

1. What version of bluebird is the issue happening on?
   v3.4.7

2. What platform and version?
   v7.5.0
   Darwin Alans-MacBook-Pro.local 15.6.0 Darwin Kernel Version 15.6.0: Mon Jan 9 23:07:29 PST 2017; root:xnu-3248.60.11.2.1~1/RELEASE_X86_64 x86_64

3. Did this issue happen with earlier version of bluebird?
   Yes

Bluebird.props should return an empty ES6 Map instead of a plain object {} when called with an empty Map:

[benjamingr]

I'm not sure I agree. Promise.props is just for returning multiple named values and passing it a map as configuration is a nice bonus - but Bluebird can't be expected to deal with every case.

[alanhoff]

@benjamingr I don't think it's about dealing with every case (empty Map only?) but not being predictable is what hurts the most. I'm ok with it if we add it to the docs:

The promise's fulfilment value is an object or a Map with fulfilment values at respective keys to the original object or a Map unless it's an empty Map, in this case it will return an empty object.

Don't you think it seems highly inconvenient? The resolved value depends on the number of items inside a Map

[bsiddiqui]

@benjamingr seems like odd behavior that Promise.props called with a Map sometimes returns a Map and sometimes returns an Object.

You're totally right that passing it a map as a configuration is a nice bonus but feels like if Bluebird is going to include that functionality it should be consistent and predictable.

[spion]

👍 different return value types are strange