Feature Request: type for Arguments OF Function

Search Terms

Suggestion

current typescript support ...args
but when we use

declare function a(x: number, y: number) : number
declare function a(x: number, s: string) : string

a(...[1, 2]) // => Error: TS2556: Expected 2 arguments, but got 0 or more.

will get error

Use Cases

Examples

declare function a(x: number, y: number) : number
declare function a(x: number, s: string) : string

Actual behavior:

a(...[1, 2]) // => Error: TS2556: Expected 2 arguments, but got 0 or more.

type ArgumentsOFFunction<T extends Function>

a type can let typescript know this is args array of target function

notice: this type is not exists

Expected behavior:

let args1: ArgumentsOFFunction<typeof a> = [x = 1, s = ''];
let args2: ArgumentsOFFunction<typeof a> = [x = 1, y = 2];
let args3: ArgumentsOFFunction<typeof a> = ['1', 2]; // trigger a ts error => Error: TS2345: Argument of type '"1"' is not assignable to parameter of type 'number'.

a(...args1) // => string
a(...args2) // => number

a(1, 'str') // => string
a(1, 2) // => number

a('1', 2) // trigger a ts error => Error: TS2345: Argument of type '"1"' is not assignable to parameter of type 'number'.

declare function b(...args: ArgumentsOFFunction<typeof a>) : boolean

b(...args1) // => boolean
b(...args2) // => boolean

b(1, 'str') // => boolean
b(1, 2) // => boolean

b('1', 2) // trigger a ts error => Error: TS2345: Argument of type '"1"' is not assignable to parameter of type 'number'.

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

No file, test, or compiler entry point is named in the issue. Start by clarifying the intended behavior for overloaded functions, tuple arguments, and generic rest parameters, then add compiler tests covering the proposed ArgumentsOFFunction type, valid calls, and the shown type errors.