Update
这是其中一种情况,其中类型推断 https://www.typescriptlang.org/docs/handbook/type-inference.html与电流承诺类型声明 https://github.com/microsoft/TypeScript/blob/065a996345fcfafd3c744d2a724a1ae9f31f9ab0/lib/lib.es2015.promise.d.ts#L41-L113失败。
最简单的解决方案是手动添加泛型类型参数:
const promisable: Promisable = ...
const res = await Promise.all<string | number>([promisable()]);
// res: (string|number)[]
你可能会推断string | number
自动地:
type PromiseReturn<T> = T extends () => Promise<infer I> ? I : never
const res = await Promise.all<PromiseReturn<Promisable>>([promisable()]);
With 打字稿 4.1 https://devblogs.microsoft.com/typescript/announcing-typescript-4-1/:更复杂的、可能嵌套的 Promise 类型可以通过自定义递归Awaited type https://devblogs.microsoft.com/typescript/announcing-typescript-4-1/#recursive-conditional-types像这样:
type Awaited<T> = T extends PromiseLike<infer U> ? Awaited<U> : T;
操场 https://www.typescriptlang.org/play?#code/KYDwDg9gTgLgBAbzgXwLACgMwJ5mHABSggFsBLAZwEMAjAG3wF44AKFgSjkYD5DjyKwADwUYUMgDsA5t04AfVhy68ipSsIkBXEjWBRZAbiy58qgcABKwGJqgShAFV7MHcUDGASAJhVacefGqCQpIAZnpwAJK8APxRcABccBLAAG56GBhewADGdFRQ+DkQEqJwYPyUtAxJZlX0wJnoxaXwUACMXHBUAO5UZPB1ggB0VHR0ImKSUnAKWjp63CwA2hVB1cAcALrsBnAA9PtwhRRJLKLi0rPJ2rpQ7MtbGC1lUABMXb39g5UjYxNDSzWWz2IYbbhLVa-DbbXYHI4nM4XabXeZ3B5PTDoHB4OAAQT6A2AXkczjgrncnh8gXMABkyABrYRhCIAVVi+MJHhJ7MS5KMzRKrwAzJ8uTT1KNxkICd9iUIrDY7A4TEIwQ0IZC1gIYewdntDsdgKdWMirnNbnoMUA
旧答案
Update: The awaited
类型运算符是延迟到更高版本 https://github.com/microsoft/TypeScript/issues/37198#issuecomment-604160291- 根本不清楚是否会发布。
这是一个已知问题 https://github.com/microsoft/TypeScript/pull/33707。好消息:TS 3.9 https://github.com/microsoft/TypeScript/issues/37198(即将推出测试版)将推出改进的承诺类型 https://github.com/microsoft/TypeScript/pull/35998:
我想重新介绍一下awaited
类型运算符来自#17077 https://github.com/microsoft/TypeScript/pull/17077满足我们对一种机制的需求,以递归方式为类似 Promise 的方法解包Promise.all
, Promise.race
, Promise.allSettled
, Promise.prototype.then
, and Promise.prototype.catch
.
of Promise.all
和其他人使用新的awaited
类型运算符。如果你使用夜间构建进行测试 https://www.typescriptlang.org/play/?ts=3.9.0-dev.20200323#code/KYDwDg9gTgLgBAbzgXwLACgMwJ5mHABSggFsBLAZwEMAjAG3wF44AKFgSjkYD5DjyKwADwUYUMgDsA5t04AfVhy68ipSsIkBXEjWBRZAbgwYAJsADGdKlHzmIE0XDD9KtBgC4%20a6vWAY7DvA2FACMXHBUAO5UZPDO3m7ASgD0yXDBIZ6i4tJwClo6ev72jsEATOFRMfCqAsAAdFR0dCwA2vECiRwAuuwGcKnpwBRlnizZklJ5cAW6UOyt3RhAA, Promise.all
现在正确解析为Promise<(string | number)[]>
:
type Promisable = (() => Promise<string>) | (() => Promise<number>);
declare const promisable: Promisable
const res = await Promise.all([promisable()]); // res: (string | number)[]
相比之下,TS 3.8无法处理它 https://www.typescriptlang.org/play/?ts=3.8.3#code/KYDwDg9gTgLgBAbzgXwLACgMwJ5mHABSggFsBLAZwEMAjAG3wF44AKFgSjkYD5DjyKwADwUYUMgDsA5t04AfVhy68ipSsIkBXEjWBRZAbgwYAJsADGdKlHzmIE0XDD9KtBgC4%20a6vWAY7DvA2FACMXHBUAO5UZPDO3m7ASgD0yXDBIZ6i4tJwClo6ev72jsEATOFRMfCqAsAAdFR0dCwA2vECiRwAuuwGcKlwesRQADRedSJiklKt3bz1i3AmmgAWq0A。对于 手动分配泛型类型参数:
declare const promisable: Promisable
const res = await Promise.all<string | number>([promisable()]); // res: (string | number)[]