Resolving promises with promises

[molnarg]

when.js does have a strange bug when resolving a promise with an other promise. Consider this code:

var when = require('when')

var a = when.defer()
  , b = when.defer()
  , c = when.defer()

a.name = 'A'
b.name = 'B'
c.name = 'C'

// 1) without when()
// a.then(function(resolved) {
// 2) with when()
when(a).then(function(resolved) {
  console.log('A resolved into', resolved.name)
})

a.resolve(b)
b.resolve(c)
c.resolve({name : 'D'})

This (second) variant prints A resolved into C. If you switch to the first variant, it prints A resolved into B.

The two variants are supposed to be equivalent aren't they?

[briancavalier]

Hey, @molnarg, when.js 1.3.0 doesn't support resolving one promise with another. However, this is implemented in the dev branch ... see #40 for more info. It'll be released soon!

[molnarg]

Thanks for the reference, I will check it out!

But I believe it is a separate issue. You write in the other ticket 'Currently, when.js will use whatever you pass to resolve() verbatim as the resolution value'. This is exactly what I expect in the example above, but something goes wrong.

If I understand the when function correctly, when(promise).then and promise.then should behave exactly the same way no matter what the resolved value will be, right? And this is not the case when you run the example above.

[briancavalier]

Yep, there is definitely weirdness in the current release. I tried your example in the dev branch, though, and it appears to work correctly. Please give it a try as well and let me know if you see the same. If not, I'll dig in deeper to figure it out before the next release.

If it looks good then expect a new release very soon. Thanks!

[briancavalier]

Just released 1.4.0 which adds support for resolving a deferred promise with another promise, and fixes the inconsistency here. Feel free to reopen this if you find any problems with it.

[molnarg]

Thank you for the hard work! :) I will check it out soon!