typescript - 如何在 typescript 中获取键类型和映射类型定义的值

Question

给定一个 Map 类型，例如:

type Foo = Map<string, number>;

有没有办法获取用于键和值的类型？

Answer 1

你可以定义一个 conditional type像这样提取您想要的任何 map 的键和值:

type Foo = Map<string, number>;

type MapKey<T> = T extends Map<infer K, any> ? K : never;
type MapValue<T> = T extends Map<any, infer V> ? V : never;

type FooKey = MapKey<Foo>
type FooValue = MapValue<Foo>

// Or if you just need it for the current case:

type FooKey2 = Foo extends Map<infer K, any> ? K : never;
type FooValue2 = Foo extends Map<any, infer V> ? V : never;