How to create async.auto-like promises chain?

Question

Here is the code I have:

async.auto({
    client: service.findClient,
    existingChat: ['client', service.findChat],
    chat: ['client', 'existingChat', service.createChat]
}, (err) => {
    if (err) return service.handleError(err);
    service.emitChatEvent();
    service.editMenu();
});

What is the best way to handle it by using Bluebird Promises?

The most confusing thing to me is this line:

 chat: ['client', 'existingChat', service.createChat]

service.createChat should have an access to both service.findClient() and service.findChat() results.

Have you tried anything yourself? I can't tell what that code does, so it's hard to know how to rewrite it using a different methodology - you at least have a clue as to what it's purpose is — Jaromanda X, Aug 23 '16 at 03:56
Your solution is looking good. If it works, why not post it as an answer instead of a question update? — Tomalak, Aug 23 '16 at 04:35
You don't really need the `return`, though. `.then((client) => [client, service.findChat(client)])` — Tomalak, Aug 23 '16 at 04:41
If you don't mind an extra lib you could check out this https://github.com/backhand/auto-promise — unflores, Dec 14 '18 at 15:07

Matt Way · Answer 1 · 2016-08-23T04:27:04.670

You could look at other already created modules like async-bluebird, or you could roll your own. By your question, it looks as though you don't necessarily need your own auto() promise implementation, just a working version of your example. In that case, you could achieve it by using a combination of chaining, and the all() function. For example (untested and off the top of my head):

let fc = service.findClient(message);
Promise.all([fc, fc.then(service.findChat)])
       .then(service.createChat);

Firstly, I create a promise from the findClient function, and then I create an array of required promises for the all function. The first is the initial promise, while the second is a chained version of the first into the second function. When both of those have completed, the all function returns the results of both promises into a results array.

score 0 · Accepted Answer · answered Aug 23 '16 at 04:56

0

I guess I've found the solution:

service.findClient(message)
    .then((client) => [client, service.findChat(client)])
    .spread(service.createChat)
    .then(service.emitChatEvent)
    .then(service.editMenu)
    .catch(service.handleError);

answered Aug 23 '16 at 04:56

Nazar

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How to create async.auto-like promises chain?

2 Answers2