Evolution of the Heroku CLI: 2008-2017

Re:Evolution of the Heroku CLI: 2008-2017 by petepete on Sunday September 03, 2017 @05:20AM (#15160467)

Instead of using Promise.all, wouldn't an approach like this work?

    const a = taskA();
    const b = taskB();
    const c = taskC();

    const result = [await a, await b, await c];

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Re:Evolution of the Heroku CLI: 2008-2017 by itwy on Sunday September 03, 2017 @11:42AM (#15161999)

These are not the same. Promise.all guarantees a is executed then b then c.

Your version guarantees the three are executed before moving forward. The order may differ on each run.

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Re:Evolution of the Heroku CLI: 2008-2017 by exogen on Sunday September 03, 2017 @02:04PM (#15162843)

FYI, Promise.all does not guarantee that. It doesn't orchestrate actually running the Promises at all (this is impossible the way Promises work), just that they're all resolved at the end, with results in the same order they were passed in.

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Re:Evolution of the Heroku CLI: 2008-2017 by itwy on Sunday September 03, 2017 @02:42PM (#15163063)

What is the difference then?

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Re:Evolution of the Heroku CLI: 2008-2017 by hdhzy on Sunday September 03, 2017 @03:37PM (#15163394)

None from the perspective of the consumer.

The implementation of Promise.all could use one array for results and fill it in any order as soon as any promise resolves while awaits will always proceed in strict order (like a generator). But that's an implementation detail that a JS programmer doesn't need to think about.

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Re:Evolution of the Heroku CLI: 2008-2017 by itwy on Sunday September 03, 2017 @04:14PM (#15163603)

Thanks for the clarification.

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Re:Evolution of the Heroku CLI: 2008-2017 by cropsieboss on Sunday September 03, 2017 @05:22AM (#15160472)

I believe `await` is sequential in the scope. `Promise.all` would be truly parallel.

edit: just checked and your version is indeed parallel. Interesting.

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Re:Evolution of the Heroku CLI: 2008-2017 by dvlsg on Sunday September 03, 2017 @05:37AM (#15160521)

Yup - all promises are "started" before you await them.

I still typically prefer Promise.all though. It's a bit more obvious what's going on (IMO) and you can skip the additional lines for assigning the promises to variables.

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Re:Evolution of the Heroku CLI: 2008-2017 by styfle on Sunday September 03, 2017 @09:41AM (#15161364)

Very cool, I never thought about doing it this way!

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