如何从Typescript中的函数获取参数类型 [英] How to get argument types from function in Typescript

问题描述

我可能遗漏了文档中的某些内容，但我在打字稿中找不到任何方法来获取函数中参数的类型.也就是说，我有一个函数

I may have missed something in the docs, but I can't find any way in typescript to get the types of the parameters in a function. That is, I've got a function

function test(a: string, b: number) {
    console.log(a);
    console.log(b)
}

我想访问类型 string 和 number，可能是元组.

I want access to the types string and number, likely as a tuple.

我知道我可以获取函数本身的类型，如 typeof test，或者通过 ReturnType 获取返回类型.

I know I can get the type of the function itself, as typeof test, or the return type via ReturnType<test>.

当我尝试keyof typeof test时，它返回never，我也无法解释.

When I tried keyof typeof test, it returned never, which I also couldn't explain.

其他答案像这个指向extends，但我真的不明白它是如何工作的，也没有给我一个简单的方法来访问 set-of-all-params 作为一种类型.

Other answers like this one point to extends, but I don't really understand how that works and don't give me an easy way to access the set-of-all-params as a type.

推荐答案

Typescript 现在带有 标准库中预定义的Parameters类型别名，与ArgumentTypes<>几乎相同 下面，所以你可以使用它而不是创建你自己的类型别名.

Typescript now comes with a predefined Parameters<F> type alias in the standard library which is almost the same as ArgumentTypes<> below, so you can just use that instead of creating your own type alias.

type TestParams = Parameters<(a: string, b: number) => void> // [string, number]

然后要获取例如第二个参数的类型，您可以使用数字索引运算符:

Then to get for example the second parameter's type you can use the numeric indexing operator:

type SecondParam = TestParams[1] // number

原答案:

是的，现在 TypeScript 3.0 引入了处于静止/展开位置的元组，您可以创建一个条件类型来做到这一点:

Yes, now that TypeScript 3.0 has introduced tuples in rest/spread positions, you can create a conditional type to do this:

type ArgumentTypes<F extends Function> = F extends (...args: infer A) => any ? A : never;

让我们看看它是否有效:

Let's see if it works:

type TestArguments = ArgumentTypes<typeof test>; // [string, number]

看起来不错.请注意，这些增强的元组还捕获了诸如可选参数和其余参数之类的内容:

Looks good. Note that these beefed-up tuples also capture things like optional parameters and rest parameters:

declare function optionalParams(a: string, b?: number, c?: boolean): void;
type OptionalParamsArgs = ArgumentTypes<typeof optionalParams>; 
// [string, (number | undefined)?, (boolean | undefined)?]

declare function restParams(a: string, b: number, ...c: boolean[]): void;
type RestParamsArgs = ArgumentTypes<typeof restParams>;
// [string, number, ...boolean[]]

希望有所帮助.祝你好运！

Hope that helps. Good luck!

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