TypeScript typeof Function return value

Question

Admit I have a function like this

const createPerson = () => ({ firstName: \'John\', lastName: \'Doe\' })

How can I, without dec

Answer 1

Adapted from https://github.com/Microsoft/TypeScript/issues/14400#issuecomment-291261491

const fakeReturn = (fn: () => T) => ({} as T)

const hello = () => 'World'
const helloReturn = fakeReturn(hello) // {}

type Hello = typeof helloReturn // string

The example in the link uses null as T instead of {} as T, but that breaks with Type 'null' cannot be converted to type 'T'.

The best part is that the function given as parameter to fakeReturn is not actually called.

Tested with TypeScript 2.5.3

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TypeScript 2.8 introduced some predefined conditional types, including the ReturnType that obtains the return type of a function type.

const hello = () => 'World'

type Hello = ReturnType // string