How to construct a promise chain involving multiple dependence?

Question

I want to construct a promise chain as below. The arrows represent dependence: B needs the output of A; C needs the outputs of both A and B.

Since it is not simply a chain but is a net, I don't know how to do it in an elegant way. My idea is to let the output of B contain the output of A, and pass it all together to C through edge (B,C). I guess it's probably not the best way to do it because there should be some method by passing the result of A directly to C.

AngularJS promise chain

This question is really about promises, and could be implemented in any framework; it's not Angular.js specific. — Claies, Jun 11 '15 at 23:46

Phil · Accepted Answer · 2015-06-12T01:04:46.233

3

If you really want to provide C with the independent promise results, try something like this

var promises = { a: A() };
promises.b = promises.a.then(function(a) {
    return B(a);
});

Promise.all(promises).then(function(results) {
    C(results.a, results.b);
});

Otherwise, I see no problem with

A().then(function(a) {
    B(a).then(function(b) {
        C(a, b);
    });
});

but really, these are just two ways of writing the same thing.

edited Jun 12 '15 at 01:04

answered Jun 11 '15 at 23:37

Phil

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I think second one is much more self explanatory. – adt Jun 11 '15 at 23:48
@FelixKling OP initially tagged as Angular. – Phil Jun 12 '15 at 00:07
1

Ah. Still, `Promise.all` is standard :) – Felix Kling Jun 12 '15 at 00:44
@Phil , I think you forgot to add `return`... – mido Jun 12 '15 at 00:53
@mido22 `return` where? – Phil Jun 12 '15 at 00:58
@Phil, `return B(a).then...`, `return C(a, b);`, – mido Jun 12 '15 at 00:59
@mido22 OP doesn't mention requiring anything further than processing C. Given the arbitrary and rather academic nature of the question, adding such implementation details is out of scope. So in other words, no, I did not *"forget to add `return`"* – Phil Jun 12 '15 at 01:00
@FelixKling: Standard `Promise.all` doesn't take objects however. It only operates on iterables. – Bergi Jun 14 '15 at 21:54
@Bergi: Right, didn't realize this was an object. – Felix Kling Jun 14 '15 at 21:55
@Bergi objects aren't iterable? – Phil Jun 14 '15 at 23:45
@Phil: Most of them, yes. Only array objects, iterators, and everything else with an method are iterable. All objects are `Reflect.enumerate`able, though. – Bergi Jun 14 '15 at 23:55

How to construct a promise chain involving multiple dependence?

1 Answers1