Here's a quick overview of the "revealing constructor" pattern, if it
helps: https://blog.domenic.me/the-revealing-constructor-pattern/
-----
Isiah Meadows
m...@isiahmeadows.com
www.isiahmeadows.com
On Wed, Jul 25, 2018 at 7:05 AM, Herbert Vojčík <he...@mailbox.sk> wrote:
>
>
> Isiah Meadows wrote on 20. 7. 2018 3:13:
>>
>> Sometimes, it's *very* convenient to have those `resolve`/`reject`
>> functions as separate functions. However, when logic gets complex
>> enough and you need to send them elsewhere, save a continuation, etc.,
>> it'd be much more convenient to just have a capability object exposed
>> more directly rather than go through the overhead and boilerplate of
>> going through the constructor with all its callback stuff and
>> everything.
>>
>> It's surprisingly not as uncommon as you'd expect for me to do this:
>>
>> ```js
>> let resolve, reject
>> let promise = new Promise((res, rej) => {
>> resolve = res
>> reject = rej
>> })
>> ```
>>
>> But doing this repeatedly gets *old*, especially when you've had to
>> write it several dozen times already. And it comes up frequently when
>> you're writing lower-level async utilities that require saving promise
>> state and resolving it in a way that's decoupled from the promise
>> itself.
>>
>> -----
>>
>> So here's what I propose:
>>
>> - `Promise.newCapability()` - This basically returns the result of
>> [this][1], just wrapped in a suitable object whose prototype is
>> %PromiseCapabilityPrototype% (internal, no direct constructor). It's
>> subclass-safe, so you can do it with subclasses as appropriate, too.
>> - `capability.resolve(value)` - This invokes the implicit resolver
>> created for it, spec'd as [[Resolve]].
>> - `capability.reject(value)` - This invokes the implicit rejector
>> created for it, spec'd as [[Reject]].
>> - `capability.promise` - This returns the newly created promise.
>>
>> Yes, this is effectively a deferred API, but revealing constructors
>> are a bit too rigid and wasteful for some use cases.
>
>
> Don't understand "revealing constructors". Can be done is userland in a few
> lines. https://lolg.it/herby/deferred-lite
>
>> [1]: https://tc39.github.io/ecma262/#sec-newpromisecapability
>>
>> -----
>>
>> Isiah Meadows
>> m...@isiahmeadows.com
>> www.isiahmeadows.com
>> _______________________________________________
>> es-discuss mailing list
>> es-discuss@mozilla.org
>> https://mail.mozilla.org/listinfo/es-discuss
>>
>
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