第二个函数参数的条件类型 [英] Conditional type of second function argument

问题描述

我具有以下功能:

function doSomething(param1: string, param2: string) {
  return param1 + param2;
}

我也有基于json的类型，其结构类似于此:

also I have json based type with structure looking similar to this:

a1: {
  b1: 'something1',
  b2: 'something2',
  b3: 'something3'
},
a2: {
  c1: 'something4',
  c2: 'something5'
}

...etc

我希望提到的函数的第n个参数为第n个深层元素的文字，因此如果第一个参数为'a1'，则第二个应为'b1' | 'b2' | 'b3'，如果第一个参数为'a2'，则第二个应为'c1' | 'c2'.

I want nth argument of mentioned function to be literal of nth deep elements, so if first argument is 'a1', second should be 'b1' | 'b2' | 'b3', and if first argument is 'a2', second should be 'c1' | 'c2'.

对于第一个参数，我已经做了简单的keyof typeof data类型，该类型很好用:

For first argument I've made simple keyof typeof data type, which is working great:

// data is imported json
type FirstArg = keyof typeof data;

我第二次尝试这样的通用类型，但没有成功:

For second I was trying generic type like this, but without success:

type SecondArg<T extends FirstArg> = keyof typeof data[T];

有机会这样做吗?

推荐答案

对于任何数量的参数，您都无法做到这一点，您可以为特定深度定义重载:

You can't do it for any number of arguments, you can define overloads for up to a specific depth:

const data = {
    a1: {
        b1: 'something1',
        b2: 'something2',
        b3: 'something3'
    },
    a2: {
        c1: 'something4',
        c2: 'something5'
    }
}
type DataType = typeof data;
function doSomething<K extends keyof DataType, K2 extends keyof DataType[K]>(p1: K, p2: K2, p3: keyof DataType[K][K2]): string
function doSomething<K extends keyof DataType>(p1: K, p2: keyof DataType[K]): string
function doSomething(p1: keyof DataType): string
function doSomething(...keys: PropertyKey[]) {
    return keys.join('.');
}

doSomething("a1", "b1")
doSomething("a1", "c2") // err

这篇关于第二个函数参数的条件类型的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！