TypeScript: Infer type of callback function parameter

Question

I am passing a callback function as a function parameter, and I need to know the type of this parameter. I don't want to define the type manually as it's too complicated. VSCode can infer the parameter type, but how can I get a type alias?

Is there some methods like ReturnType and InstanceType that can do the job?

Tobias S. · Accepted Answer · 2022-05-27 13:04:56Z

3

This should correctly infer the type of response:

type AddProfileResponseType = 
  typeof onAddProfileDone extends (cb: (r: infer R) => any) => any 
    ? R 
    : never

If the library defines a type for the onAddProfileDone function. You should use it instead of typeof onAddProfileDone.

Playground

Or even simpler:

type AddProfileResponseType = Parameters<Parameters<typeof onAddProfileDone>[0]>[0]

Playground

edited May 27, 2022 at 13:04

answered May 27, 2022 at 5:52

Tobias S.

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1 Comment

Huakun Shen Over a year ago

Thanks the second one works for me! Didn't try the first version.

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