Typescript 仅从重载中选择特定方法（将传递给 Parameters<T>）

Question

背景

所以我在从重载的函数中获取特定参数时遇到了问题。例如：

// someLib.d.ts
type Component<T> = {};
type A = {};
type B = {};
type C = {};
type Opts = {};
type ModernOpts = {};

export declare function mount(component: A, options: Opts): Component<A>;
export declare function mount(component: B, options: Opts): Component<B>;
export declare function mount(component: C, options: ModernOpts): Component<C>;

问题是，如果我在另一个文件上这样做：

import { mount } from 'someLib';

type specificMountParams = Parameters<typeof mount>;

我得到的参数是[C, ModernOpts]，好像没办法得到[A, Opts]的参数，或者[B, Opts].

问题

有没有办法从重载函数中检索特定参数？（所以我可以获得[A, Opts]参数）

限制和信息

这些类型 (A, B, Opts) 没有被库导出，我需要创建一个需要这种类型的函数来做类似的事情。

Answer 1

来自docs:

When inferring from a type with multiple call signatures (such as the type of an overloaded function), inferences are made from the last signature (which, presumably, is the most permissive catch-all case). It is not possible to perform overload resolution based on a list of argument types.

C考虑这个例子：

function foo(a: number): number
function foo(a: string): string // last signature
function foo(a: number | string): number | string {
  return null as any
}

type Fn = typeof foo

// returns last overloaded signature
type Arguments = Parameters<Fn> // [a: string]

Parameters 始终是 return 函数的最后一个重载签名。

尝试更改顺序：

function foo(a: string): string 
function foo(a: number): number// last signature
function foo(a: number | string): number | string {
  return null as any
}

type Fn = typeof foo

// returns last overloaded signature
type Arguments = Parameters<Fn> // [a: number]

无法return所有参数的并集，因为它不可靠。看官方解释here

It's not really possible to make this in a way that's both useful and sound. Consider a function like
declare function fn(n1: number, n2: number): void;

declare function doCall<T extends (a1: any, a2: any) => void>(func: T,
a0: Parameters<T>[0], a1: Parameters<T>[1]): void; ```

If Parameters<T>[0] returns string | number, then doCall(fn, 0, "") would incorrectly succeed. If Parameters<T>[0]> returns string & number, then doCall(fn, 0, 0) would incorrectly fail (and be a big breaking change). Notably, with conditional types and unions, really the only kind of functions that can't be typed with a single overload are exactly the ones that have this failure mode.

目前的行为至少可以正确接受一些呼叫。

您可以在上面的 github 线程中找到一些解决方法

Typescript 仅从重载中选择特定方法（将传递给 Parameters<T>）

Typescript pick only specific method from overload (to be passed to Parameters<T>)

parameters

methods

overloading

utility

typescript

背景

问题

限制和信息