Typescript: Add `PromiseResult` type to standard lib

Created on 24 Oct 2018 · 6Comments · Source: microsoft/TypeScript

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:

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

In Discussion Suggestion

Source

ethanresnick

👍6

Most helpful comment

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.

DanielRosenwasser on 24 Oct 2018

👍2

All 6 comments

See #17077, and discussion at

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

DanielRosenwasser on 24 Oct 2018

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.

DanielRosenwasser on 24 Oct 2018

👍2

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

ajafff on 24 Oct 2018

Any progress here? :)

deser on 12 Dec 2019

👀2

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.