Microsoft/TypeScript

Assigning a @type to an async function emits an error

Open

#58,215 opened on Apr 16, 2024

View on GitHub
 (1 comment) (1 reaction) (0 assignees)TypeScript (6,726 forks)batch import
BugDomain: JSDocHelp Wanted

Repository metrics

Stars
 (48,455 stars)
PR merge metrics
 (Avg merge 6d 17h) (9 merged PRs in 30d)

Description

🔎 Search Terms

ts1065 jsdoc async return promise

🕗 Version & Regression Information

  • This changed between versions 5.1.6 and 5.2.2

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.2.2&filetype=js#code/PQKhAIAEBcE8AcCmATRAzcBvAFASnALwB84ACgE4D2AtgJYDOiAPAG6W3IkA+4bHAvuACC9WADsAxgDEx4EMABQC0BBgJEWEeOljB8hRMpj60cNVhbJMwuACGoyeDyESmfkA

💻 Code

JSDoc version:

/** @typedef {() => Promise<void> | void} AsyncFn */

/** @type {AsyncFn} */
const myAsyncFn = async () => {}

TypeScript equivalent:

type AsyncFn = () => Promise<void> | void;

const myAsyncFn : AsyncFn = async () => {}

🙁 Actual behavior

JSDoc version emits an error, TypeScript equivalent does not.

🙂 Expected behavior

Neither should emit an error.

Additional information about the issue

I'm fairly sure this is related to a change from a while back where a new Promise needs to be explicitly marked as returning Promise<void>, which was intentional. But I can't seem to find the related issue anymore so I'm not sure if this is intentional as well.

Either way, the fact that this error is only emitted in JavaScript files seems to suggest that it's a bug.

Contributor guide

Research direction
Identify the specific commit or change between TypeScript 5.1.6 and 5.2.2 that introduced the error. Compare the type checking behavior for JSDoc typed async functions versus TypeScript typed async functions. Understand why the JSDoc case produces an error while the TS equivalent does not, and determine if it's intentional or a bug.
Tech stack
typescriptjavascript
Domain
compilers
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
TypeScriptJSDoc
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70