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Awaited

介绍​

假如我们有一个 Promise 对象，这个 Promise 对象会返回一个类型。在 TS 中，我们用 Promise<T> 中的 T 来描述这个 Promise 返回的类型。请你实现一个类型，可以获取这个类型。

例如：Promise<ExampleType>，请你返回 ExampleType 类型。

This question is ported from the original article by @maciejsikora

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起点​

ts
/* _____________ Your Code Here _____________ */
type Awaited<T> = any;
Duplicate identifier 'Awaited'.2300Duplicate identifier 'Awaited'.
 
/* _____________ Test Cases _____________ */
type X = Promise<string>;
type Y = Promise<{ field: number }>;
 
type cases = [
  Expect<Equal<Awaited<X>, string>>,
  Expect<Equal<Awaited<Y>, { field: number }>>
];
ts
/* _____________ Your Code Here _____________ */
type Awaited<T> = any;
Duplicate identifier 'Awaited'.2300Duplicate identifier 'Awaited'.
 
/* _____________ Test Cases _____________ */
type X = Promise<string>;
type Y = Promise<{ field: number }>;
 
type cases = [
  Expect<Equal<Awaited<X>, string>>,
  Expect<Equal<Awaited<Y>, { field: number }>>
];
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解决方案​

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ts
// type Awaited<T extends Promise<unknown>> = T extends Promise<infer R> ? R : never;
type Awaited<T extends Promise<unknown>> = T extends Promise<infer R> ? R extends Promise<unknown> ? Awaited<R> : R : never
Duplicate identifier 'Awaited'.2300Duplicate identifier 'Awaited'.
ts
// type Awaited<T extends Promise<unknown>> = T extends Promise<infer R> ? R : never;
type Awaited<T extends Promise<unknown>> = T extends Promise<infer R> ? R extends Promise<unknown> ? Awaited<R> : R : never
Duplicate identifier 'Awaited'.2300Duplicate identifier 'Awaited'.
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