Promise progress handlers firing in wrong order on a settled promise

[simonzack]

The following prints 2 then 1. Shouldn't it be the other way around?

var Promise = require('bluebird');

function main(){
    var resolver = Promise.defer();
    resolver.progress(1);
    resolver.resolve(2);
    var promise = resolver.promise;

    promise.then(function(res){
        console.log(res);
    }).progressed(function(res){
        console.log(res);
    });
}

main();

[gaearon]

Why should it?

I don't know if you meant it, but you're listening to progressed on a promise returned by then, not on the original promise.

I'm not sure if spec covers it, but in my view it makes sense for second promise's progressed to execute later then first promises' then.

This code prints 1 2 as you intended:

var Promise = require('bluebird');

function main(){
    var resolver = Promise.defer();
    resolver.progress(1);
    resolver.resolve(2);
    var promise = resolver.promise;

    promise.then(function(res){
        console.log(res);
    });

    promise.progressed(function(res){
        console.log(res);
    });
}

main();

I'm not sure if it's right though: this draft specifically says “onProgress is never called once a promise has already been fulfilled or rejected.”

If this is the case, maybe this code should only print 2 since promise was already resolved by the time we subscribed to its progress. (It does print 2 if we call then and progressed in next tick.)

[simonzack]

Yes I think that makes sense too now, I interpreted this as having both listeners being on the same promise. Thanks for explaining this.

[gaearon]

@simonzack No problem. then always returns a new promise. See this iconic post on how jQuery stubbornly insisted on getting it wrong.