TypeScript Convert Parameters Array to Tuple Array

given

function fn(a:number, b:number, c:number): void {}    type T1 = Parameters<typeof fn> // [a:number, b:number, c:number]  

I would like to

  type T2<T1> = /* how?! --> [number, number, number] */    

Why?

I would like to assign an "untyped" value to a variable of type T1, but it doesn't work:

type T1 = Parameters<typeof fn> // [a:number, b:number, c:number]    let foo = [1, 2, 3] // inferred type --> number[]  let bar: T1 = foo // Error: Target requires 3 element(s) but source may have fewer.ts(2322)  

It works like this (typed foo):

let foo: [number, number, number] = [1, 2, 3]  let bar: T1 = foo // ok!  

To get around this, I would like to create a new type T2 based on T1 which would "mirror" the parameters of fn as tuple array (which accepts the inferred type number[]). This way I would have type safety (length and type of fn parameters) but could pass "untyped" values to a T2 typed variable:

type T2<T1> = /* how?! --> [number, number, number] */    let foo = [1, 2, 3] // inferred type --> number[]  let bar: T2 = foo // ok!  let bar: [number, number, number] = foo // ok!  

Thanks!

https://stackoverflow.com/questions/65755553/typescript-convert-parameters-array-to-tuple-array January 17, 2021 at 06:51AM