TypeScript中的等待类型 [英] Awaitable type in TypeScript

问题描述

我在JavaScript中使用async/等待很多.现在，我逐渐将代码库的某些部分转换为TypeScript.

I use async / await a lot in JavaScript. Now I’m gradually converting some parts of my code bases to TypeScript.

在某些情况下，我的函数接受将被调用并等待的函数.这意味着它可以返回一个promise，而只是一个同步值.我为此定义了 Awaitable 类型.

In some cases my functions accept a function that will be called and awaited. This means it may either return a promise, just a synchronous value. I have defined the Awaitable type for this.

type Awaitable<T> = T | Promise<T>;

async function increment(getNumber: () => Awaitable<number>): Promise<number> {
  const num = await getNumber();
  return num + 1;
}

可以这样称呼:

// logs 43
increment(() => 42).then(result => {console.log(result)})

// logs 43
increment(() => Promise.resolve(42)).then(result => {console.log(result)})

这有效.但是，必须为我所有使用async/await和TypeScript的项目指定 Awaitable ，这很烦人.

This works. However, it is annoying having to specify Awaitable for all of my projects that use async/await and TypeScript.

我真的不能相信没有内置这种类型，但是我找不到.TypeScript是否具有内置的等待类型?

I can’t really believe such a type isn’t built in, but I couldn’t find one. Does TypeScript have a builtin awaitable type?

推荐答案

我相信这个问题的答案是:不，没有内置类型.

I believe the answer to this question is: No, there is no built-in type for this.

在 lib.es5.d.ts 和 lib.es2015.promise.d.ts ，它们使用 T |PromiseLike< T> 对于您的 Awaitable< T> 有意义的各个地方，例如:

In lib.es5.d.ts and lib.es2015.promise.d.ts, they use T | PromiseLike<T> for the various places your Awaitable<T> would make sense, for instance:

/**
 * Represents the completion of an asynchronous operation
 */
interface Promise<T> {
    /**
     * Attaches callbacks for the resolution and/or rejection of the Promise.
     * @param onfulfilled The callback to execute when the Promise is resolved.
     * @param onrejected The callback to execute when the Promise is rejected.
     * @returns A Promise for the completion of which ever callback is executed.
     */
    then<TResult1 = T, TResult2 = never>(onfulfilled?: ((value: T) => TResult1 | PromiseLike<TResult1>) | undefined | null, onrejected?: ((reason: any) => TResult2 | PromiseLike<TResult2>) | undefined | null): Promise<TResult1 | TResult2>;

    /**
     * Attaches a callback for only the rejection of the Promise.
     * @param onrejected The callback to execute when the Promise is rejected.
     * @returns A Promise for the completion of the callback.
     */
    catch<TResult = never>(onrejected?: ((reason: any) => TResult | PromiseLike<TResult>) | undefined | null): Promise<T | TResult>;
}

在 lib.es5.d.ts 中没有什么像您的 Awaitable ，它们在其中定义 PromiseLike 和 Promise

There's nothing like your Awaitable in lib.es5.d.ts where they define PromiseLike and Promise.

我想如果他们定义了一个，他们会在这些定义中使用它.

I'd think if they'd defined one, they would use it in those definitions.

旁注:根据这些定义，在您的 Awaitable 中使用 PromiseLike 而不是 Promise 可能是有意义的:

Side note: Based on those definitions, it probably makes sense to use PromiseLike rather than Promise in your Awaitable:

type Awaitable<T> = T | PromiseLike<T>;

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