Flatter calls using promises: avoiding callbackception

Question

I have found the following use case while working with promises. I am writing CoffeeScript for concision but the reading for JavaScript developers should be straight forwards

getUserName().then (userName) ->
  getRelatedCompany(userName).then (relatedCompany) ->
    registerConnexion(userName, relatedCompany)

In the above all request depend of the above results of the previous ones. What's the proper way to solve this to get something like this:

getUserName().then (userName) ->
  getRelatedCompany(userName)
.then (relatedCompany) ->
  # in that example, userName would be undefined here but there's less callbackception
  registerConnexion(userName, relatedCompany)

EDIT: I am using bluebird as promise library.

Benjamin Gruenbaum · Accepted Answer · 2014-12-06T12:05:05.057

1

You can use promises as proxies that represent values:

username = getUserName()
company = username.then(getRelatedCompany)
// assuming good promise lib, otherwise shim .spread of nest once
connexion = Promise.all([username, company]).spread(registerConnexion)

In bluebird, this is even simpler and becomes:

username = getUserName()
company = username.then(getRelatedCompany)
connexion = Promise.join(username, company, registerConnexion);

Since .join was designed for this use case in mind.

edited Dec 06 '14 at 12:05

answered Dec 05 '14 at 23:44

Benjamin Gruenbaum

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I am using bluebird as a promise library. I have edited your answer to fix a typo! Thanks! – AsTeR Dec 06 '14 at 12:02
@AsTeR editing to include a Bluebird answer, update soon. – Benjamin Gruenbaum Dec 06 '14 at 12:04
I guess your StackExchange account description is a kind of rickroll... you got me ;) ! – AsTeR Dec 06 '14 at 12:40

Flatter calls using promises: avoiding callbackception

1 Answers1