Decouple $q in AngularJS 2.0 (and/or switch to bluebird)

[mgcrea]

AngularJS currently uses a shim of q. I haven't dug into the actual implementation, but I think it might be interesting to review a possible change for the 2.0 milestone.

I think AngularJS should use an agnostic $Promise service accross the framework, and extract the current $q shim out of the core. Letting user choose their Promise framework. Thanks to the unified promise spec, this should be doable.

Also, I would strongly advise to pick bluebird over q for the future.

I've been doing NodeJS work for a couple of years, and switching from q to the very well-crafted bluebird has been a really pleasant experience. The API is far superior and the performance is unmatched.

Regarding performance, have a look at this article.

But you said promises are slow!
Yes, I know I wrote that. But I was wrong. A month after I wrote the giant comparison of async patterns, Petka Antonov wrote Bluebird. Its a wicked fast promise library, and here are the charts to prove it.

file	time(ms)	memory(MB)
callbacks-original.js	316	34.97
callbacks-flattened.js	335	35.10
callbacks-catcher.js	355	30.20
promises-bluebird-generator.js	364	41.89
dst-streamline.js	441	46.91
callbacks-deferred-queue.js	455	38.10
callbacks-generator-suspend.js	466	45.20
promises-bluebird.js	512	57.45
thunks-generator-gens.js	517	40.29
thunks-generator-co.js	707	47.95
promises-compose-bluebird.js	710	73.11
callbacks-generator-genny.js	801	67.67
callbacks-async-waterfall.js	989	89.97
promises-bluebird-spawn.js	1227	66.98
promises-kew.js	1578	105.14
dst-stratifiedjs-compiled.js	2341	148.24
rx.js	2369	266.59
promises-when.js	7950	240.11
promises-q-generator.js	21828	702.93
promises-q.js	28262	712.93

[caitp]

We're probably going to be using ES6 promises in Angular 2.0. I can't promise that the digest cycle will be separated from $q in 1.x, but that's really the big thing that gets in the way of allowing a pluggable interface, as far as I'm aware.

[gx0r]

+1 a pluggable promise interface would be great

Just a comment on native promises, They are in ES six however they don't have the superb long stacktrace support that bluebird has. Also, bluebird can do 1 million promises per second while native promises and chrome are much slower at 25,000. That might not matter to most people but it may matter to somebody.

[caitp]

Pluggable would be nice, but for the moment, it's not super feasible, because promises are tied to digest cycle. We can do this better for 2.0, but it might be very hard to remove this glue from 1.x, and that is the major barrier. In addition, it's very easy to mock the promise implementation in angular so that it can be used in tests. With a pluggable system, this is greatly complicated, and these things hurt.

In any case, we can probably use Zone.js in 1.x to enable longer stack traces like Bluebird, even with the native $q implementation. I haven't yet looked at how difficult this would be, but it seems like something which is backportable to 1.x. It's true that we could probably use a better nextTick implementation which would perform better in the browser (like setImmediate, when available), among other things, but the real performance killer of the promise implementation in Angular isn't waiting for the next tick, but performing an app-wide digest. So even with Bluebird, if it's tied to the digest cycle, you wouldn't really see an improvement here for 1,000,000 promises simultaneously.

[gx0r]

@caitp thanks for the excellent info and I didn't know about Zone.js.

[benjamingr]

+1 for decoupling it. I'd love to use a stronger promise implementation.

[quantizor]

@llambda "Also, bluebird can do 1 million promises per second while native promises and chrome are much slower at 25,000." That's crazy! I'd expect native browser methods to be an order of magnitude faster. Does that data come from Bluebird's page or somewhere else?

[benjamingr]

It comes from the fact the guy writing Bluebird has very intimate knowledge of JS engines :) Also, JS isn't slower than native when you understand the JIT in these cases.

[caitp]

V8's promises are implemented (mostly) in JS, anyways, so it's true that there is very little difference in these cases.

[benjamingr]

To clarify, I'm against including Bluebird in Angular, I'm for decoupling the architecture here, and allowing users to easily hook their own implementation.