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Running promises in order

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  Running promises in order Andrew Poulos <ap_prog@hotmail.com> - 2017-11-28 11:35 +1100
    Re: Running promises in order "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2017-11-28 13:02 +0100
    Re: Running promises in order "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2017-11-28 13:31 -0800
      Re: Running promises in order Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-12-01 02:37 +0100
        Re: Running promises in order "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2017-12-01 06:53 -0800
    Re: Running promises in order ali.abdulhannan@gmail.com - 2017-12-02 04:04 -0800

#34394 — Running promises in order

How do I run an arbitrary number of promises where the subsequent 
promise is not to run before the previous promise is fulfilled?

The values a previous promise generates is used by subsequent promises.

The various examples I've googled have the user triggering the next 
promise eg. by clicking a button.

Andrew Poulos

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#34395

Andrew Poulos <ap_prog@hotmail.com> wrote on 28 Nov 2017 in 
comp.lang.javascript:

> How do I run an arbitrary number of promises where the subsequent 
> promise is not to run before the previous promise is fulfilled?
> 
> The values a previous promise generates is used by subsequent promises.
> 
> The various examples I've googled have the user triggering the next 
> promise eg. by clicking a button.

There must be countless psychological publications about the incertaincy of 
the fullfillment of promises and their probable timespan.

Couldn't you start the execution with a test of a global variable on the 
fullfullment of the 'former' promise, and the restacking of the latter one 
on failing of the former?

-- 
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

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#34396

On Monday, November 27, 2017 at 6:35:22 PM UTC-6, Andrew Poulos wrote:
> How do I run an arbitrary number of promises where the subsequent 
> promise is not to run before the previous promise is fulfilled?
> 
> The values a previous promise generates is used by subsequent promises.
> 
> The various examples I've googled have the user triggering the next 
> promise eg. by clicking a button.

At first blush, something like the following:

promiseArray.reduce((prev, curr) => (
    prev.then(resultList => (
        asyncFunc(curr).then(result => resultList.concat(result))
    ))
), Promise.resolve([]));

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#34397

Michael Haufe (TNO) wrote:

> On Monday, November 27, 2017 at 6:35:22 PM UTC-6, Andrew Poulos wrote:
>> How do I run an arbitrary number of promises where the subsequent
>> promise is not to run before the previous promise is fulfilled?
>> 
>> The values a previous promise generates is used by subsequent promises.
>> 
>> The various examples I've googled have the user triggering the next
>> promise eg. by clicking a button.
> 
> At first blush, something like the following:
> 
> promiseArray.reduce((prev, curr) => (
>     prev.then(resultList => (
>         asyncFunc(curr).then(result => resultList.concat(result))
>     ))
> ), Promise.resolve([]));

That is a very clever (mis)use of Array.prototype.reduce() :)

-- 
PointedEars
FAQ: <http://PointedEars.de/faq> | <http://PointedEars.de/es-matrix>
<https://github.com/PointedEars> | <http://PointedEars.de/wsvn/>
Twitter: @PointedEars2 | Please do not cc me./Bitte keine Kopien per E-Mail.

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#34398

Thomas 'PointedEars' Lahn wrote:
> Michael Haufe (TNO) wrote:
> 
> > On Monday, November 27, 2017 at 6:35:22 PM UTC-6, Andrew Poulos wrote:
> >> How do I run an arbitrary number of promises where the subsequent
> >> promise is not to run before the previous promise is fulfilled?
> >> 
> >> The values a previous promise generates is used by subsequent promises.
> >> 
> >> The various examples I've googled have the user triggering the next
> >> promise eg. by clicking a button.
> > 
> > At first blush, something like the following:
> > 
> > promiseArray.reduce((prev, curr) => (
> >     prev.then(resultList => (
> >         asyncFunc(curr).then(result => resultList.concat(result))
> >     ))
> > ), Promise.resolve([]));
> 
> That is a very clever (mis)use of Array.prototype.reduce() :)

I haven't tried it, but I think using the new "async"/"await" keywords with a for...of loop would be clearer for the more traditionally minded, but I try to avoid procedural constructs:

async function foo(promiseList) {
  var resultList = []
  for(const p of promiseList) {
    resultList.push(await doPromise(p));
  }
  return resultList
};

Looks like there are a handful of alternatives approaches out there as well:

<https://stackoverflow.com/a/24586168/153209>

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#34399

On Monday, November 27, 2017 at 5:35:22 PM UTC-7, Andrew Poulos wrote:
> How do I run an arbitrary number of promises where the subsequent 
> promise is not to run before the previous promise is fulfilled?
> 
> The values a previous promise generates is used by subsequent promises.
> 
> The various examples I've googled have the user triggering the next 
> promise eg. by clicking a button.
> 
> Andrew Poulos

Happened to check this usenet group, so would like to weigh in. The reduce function is something I would use

<code lang="js">
  const pArray = [ p1, p2, p3 ];
  const fulfilledResults = [];
  pArray.reduce((prev, current) => prev.then((...args) = {
    fulfilledResults.push(args);
  })));
</code>

However if you have many of those usecases I would suggest you to check out Bluebird library which handles scenarios such as these already. Specifically check the <a href="http://bluebirdjs.com/docs/api/promise.mapseries.html">Promise.mapSeries</a> method

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