重载的打字稿功能参数不适用于async关键字

Question

I'm working on a larger project type definition file. I have simplified the code into an isolated example:

Module definition fdts

export type myFunction = ((r: string) => Promise<any>) // async def
  | ((r: string, done: (err: Error | null, b?: any) => void) => void) //callback def

export interface addFunc {
  (c: string, f: myFunction): void
}

export interface FI {
  addFunc: addFunc
}

export default function f(): FI

Module implementation f.js

function f () {
  return {
    addFunc: (c, p) => {
      this[c] = p
      return this
    }
  }
}

module.exports = f

Module utilization index.ts

import f from './f'

f().addFunc('x', (r, d) => { // Compiles as expected
  d(null)
})

f().addFunc('x', async (r) => { // Error ts(7006) Parameter 'r' implicitly has an 'any' type.
  return null
})

Can you please explain why this error is happening and how I could fix it? I believe the issue is in the type definition.

Please do not comment on the implementation itself; this is an extremely stripped down and isolated piece of a large API.

Thank you for the help!

Answer 1

You need to change it to

f().addFunc('x', async (r: string) => {
  return null
})

Without adding : string , your function is really a (r: any) => Promise<null> , which is not assignable to the type myFunction .

The first case in your example compiles because TypeScript is able to infer the types of r and d by the fact that there're two parameters, which makes it impossible to assign to the first case in the union definition of myFunction . But when a function has only one parameter, it could be assigned to a type that has one or more parameters, so TypeScript cannot automatically infer the type of r .