In Typescript: How to extract separate input and output types for a function?

Question

For this function:

function first(x: number, y: string) {
return {
    a: x,
    b: y
  };
}

function second(z: typeof first()) {
  return {
    c: 6,
    ...z
  }
}

typeof first() is, ofcourse, invalid,

I'd like to use the inferred output type of first in second's signature. Is it possible (I'm assuming no but hope to be surprised)

Thanks!

toskv · Accepted Answer · 2017-06-25 12:41:28Z

1

No, at this moment it is not possible to extract the return type of a function.

There is a thread on github where this is discussed though. You can see it here.

What you can do right now is to define a specific type to be used in as the return type of the first function and the type of the parameters received by the first function. It's also a lot more explicit and easier to understand.

interface ReturnType {
    a: number,
    b: string
}
function first(x: number, y: string): ReturnType {
    return {
        a: x,
        b: y
    };
}

function second(z: ReturnType) {
    return {
        c: 6,
        ...z
    }
}

answered Jun 25, 2017 at 12:41

toskv

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