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Add PromiseResult type to standard lib #28105

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Add PromiseResult type to standard lib#28105
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In DiscussionNot yet reached consensusSuggestionAn idea for TypeScript

Description

@ethanresnick
Ethan Resnick (ethanresnick)
opened on Oct 24, 2018

Search Terms

promise result type

Suggestion

Typescript already ships with a ReturnType type and a Parameters type, so why not ship with a PromiseResult type:

type PromiseResult<T> = T extends Promise<infer U> ? U : never;

Use Cases/Examples

type Output = PromiseResult<ReturnType<typeof computeSomething>>;

async function computeSomething(input: any) {}
function computeFromResult(input: Output) {}

Checklist

My suggestion meets these guidelines:

  • This wouldn't be a breaking change in existing TypeScript / JavaScript code
  • This wouldn't change the runtime behavior of existing JavaScript code
  • This could be implemented without emitting different JS based on the types of the expressions
  • This isn't a runtime feature (e.g. new expression-level syntax)

Activity

  1. DanielRosenwasser commented on Oct 24, 2018

    @DanielRosenwasser
    Daniel Rosenwasser (DanielRosenwasser)
    on Oct 24, 2018
    Member

    See #17077, and discussion at

    Search also for awaited, await, promised, unpromise, and unpromisify on the issue tracker.

  2. DanielRosenwasser commented on Oct 24, 2018

    @DanielRosenwasser
    Daniel Rosenwasser (DanielRosenwasser)
    on Oct 24, 2018
    Member

    Just to clarify, for Promises to work correctly we need a more general awaited type which unwraps PromiseLikes recursively. If we had that, it would subsume this PromiseResult type.

  3. ajafff commented on Oct 24, 2018

    @ajafff
    Klaus Meinhardt (ajafff)
    on Oct 24, 2018
    Contributor

    Just to clarify, for Promises to work correctly we need a more general awaited type which unwraps PromiseLikes recursively.

    Sounds like recursive conditional types to me... but that's already discussed somewhere else

  4. Daniel Rosenwasser (DanielRosenwasser)
    added
    SuggestionAn idea for TypeScript
    In DiscussionNot yet reached consensus
    on Oct 25, 2018

  5. deser commented on Dec 12, 2019

    @deser
    Alexey Petrochenkov (deser)
    on Dec 12, 2019

    Any progress here? :)

  6. westonkjones commented on Dec 19, 2019

    @westonkjones
    Wes Jones (westonkjones)
    on Dec 19, 2019

    Interested in this as well. The AWS SDK uses this as the return of their promises
    https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/SecretsManager.html#getSecretValue-property

    (method) Request<SecretsManager.GetSecretValueResponse, AWSError>.promise(): Promise<PromiseResult<AWS.SecretsManager.GetSecretValueResponse, AWS.AWSError>>

Returns a 'thenable' promise.

  7. fregante commented on Jan 11, 2020

    @fregante
    fregante
    on Jan 11, 2020

    Coming in #35998, hopefully

  8. Ethan Resnick (ethanresnick)
    closed this as completedon May 17, 2022
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