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Comment by jwalton | Hacker News Reader

If you're looking for a more lightweight solution than Bluebird (because, say, you're writing client side code - Bluebird is a bit heavy weight):

* [promise-tools](https://github.com/benbria/node-promise-tools) is a library with a lot of the cool flow control from Bluebird, but is tiny and works with native Promises.

* [promise-breaker](https://github.com/jwalton/node-promise-breaker) is a library I wrote which is intended to make it really easy for third party libraries to support both promises and callbacks with a minimum of fuss (we also use this extensively internally as we convert our giant code base from callbacks to promises.) `callFn` and `applyFn` are also very handy for calling into existing callback based libraries from within promise based libraries.

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Ah, this was exactly what I was going to ask, thanks! Promise tools looks great - do you know of any equivalents of promisify and promisifyAll? I use them a lot with native libraries.

EDIT: to answer my own question, this looks like it'll do it:

https://github.com/pgaubatz/node-es6-promisify-all

but it doesn't seem to be actively maintained.

Check out https://github.com/sindresorhus/pify

I'm looking for an approach where promises can be canceled. For example, when I'm waiting for a promise p to be fulfilled, I might suddenly decide that I'm not interested anymore in the promise. So I could call (for example) p.cancel(), and the effect would be that the underlying code is stopped (and recursively everything it depends on).

Microsoft's RxJS does all that (and more): https://xgrommx.github.io/rx-book/content/getting_started_wi...

See this specific blog post for more details (though the Rx Book is fantastic): "That said, a sore point for Promises has always been their lack of cancelability. This leads to some interesting design patterns where you have to "protect" your promise callbacks from context-dependent changes. Because of this hoop-jumping, the most attractive RxJS feature that I've seen so far is the simple ability to cancel (aka, unsubscribe, aka, dispose) an RxJS stream before it completes."

http://www.bennadel.com/blog/3030-canceling-rxjs-observables... (Though there are RxJS interops with more than just Angular)

Promises, and in particular bluebird promises, are cancellable.

ECMAscript 6 has cancellable promises? This guy[1] seems to claim otherwise. I spent 20 minutes on skimming the spec[2] and from what I can tell, there's no language feature that has that `promiseCapability'[3] and those stackoverflow workarounds remain the only native ECMAscript way to do it.

(I had to look up what that bluebird was and it looks like they both are libraries that offer cancellable functionality that the callee can invoke. So it looks like one is left to libraries regardless of Bluebird or RxJS or another solution. I'd opt for RxJS personally as RxJS is fairly first-class in the MS ecosystem (maybe one half-step beneath F#), and a lot of the product is based off of the RX research done by de Smet, Meijers, Beckman, et al (they've thrown prime engineering talent at it for years working out the concurrency semantics). But again, not in the JS ecosystem and just skimmed the standard[4] revision so there's a very high chance of me being wrong. I try to limit my comments to topics on which I'm relatively well-informed in general; in this case, please do regard my comments as poorly-informed-at-best.)

[1] http://stackoverflow.com/a/30235261 [2] https://tc39.github.io/ecma262/ [3] https://tc39.github.io/ecma262/#sec-promise-executor [4] Oh god, 25.4.4.1.1 - Runtime Semantics: PerformPromiseAll( iteratorRecord, constructor, resultCapability ). And I thought 'Rails magic' was bad. Step 6 goes all the way down from [a..r] haha.

ECMAScript doesn't have cancellable promises, but then again it doesn't have observables or async iterators either.

Native observables are less capable in this regard than native promises since they're non existent yet.

Bluebird promises are cancellable.

For what it's worth I've discussed this personally with Meijer (it's Meijer, not Meijers) and he agrees that cancellable promises are not problematic one bit.

Promises, observables and other async primitives all co-exist just fine :)

Very neat! If you are interested in high level promises without any dependencies, like these, I have a small library inspired by some of the more useful helpers in Bluebird:

[extends-promise](https://github.com/kjvalencik/extends-promise)

Fair warning, it has an emphasis on simplicity of code rather than speed. It does a few things that are very likely inefficient. I wrote it primarily to scratch an itch I had--embedding in one-off node.js scripts without any dependencies.

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