Setting function signature to custom type in TypeScript

Question

I have a function with a signature

const updateMatrix = (m: number) => (i: number, j: number, value: number): void => {

However, I need to re-use the second function's signature in other parts of my code, so I set it to a type.

export type SetMatrixValue = (i: number, j: number, value: number) => void

How can I set the type of my updateMatrix function to match that of the SetMatrix Value type?

Aleksey L. · Accepted Answer · 2020-03-05 11:26:40Z

2

You could extract the type of the second function using ReturnType utility (it is actually return type of updateMatrix):

const updateMatrix = (m: number) => (i: number, j: number, value: number): void => {}

type SetMatrixValue = ReturnType<typeof updateMatrix>; // (i: number, j: number, value: number) => void

Playground

Answering original question:

type SetMatrixValue = (i: number, j: number, value: number) => void

const updateMatrix = (m: number): SetMatrixValue => (i, j, value) => { };

edited Mar 5, 2020 at 11:26

answered Mar 5, 2020 at 11:15

Aleksey L.

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1 Comment

Perplexityy Over a year ago

I want it the other way around, I want to be able to pass the type TO the function to serve as both its arguments and return type, so I can re-use it in other functions in my code.

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