如何在 async/await 语法中拒绝? [英] How to reject in async/await syntax?

问题描述

如何拒绝由 async/await 函数返回的承诺?

How can I reject a promise that returned by an async/await function?

例如原文:

foo(id: string): Promise<A> {
  return new Promise((resolve, reject) => {
    someAsyncPromise().then((value)=>resolve(200)).catch((err)=>reject(400))
  });
}

翻译成async/await:

async foo(id: string): Promise<A> {
  try{
    await someAsyncPromise();
    return 200;
  } catch(error) {//here goes if someAsyncPromise() rejected}
    return 400; //this will result in a resolved promise.
  });
}

那么，在这种情况下，我该如何正确拒绝这个承诺?

So, how could I properly reject this promise in this case?

推荐答案

你最好的办法是 throw 一个 Error 包装值，这会导致一个被拒绝的承诺一个 Error 包装值:

Your best bet is to throw an Error wrapping the value, which results in a rejected promise with an Error wrapping the value:

} catch (error) {
    throw new Error(400);
}

你也可以只throw这个值，但是没有堆栈跟踪信息:

You can also just throw the value, but then there's no stack trace information:

} catch (error) {
    throw 400;
}

或者，返回一个被拒绝的承诺，其中包含一个 Error 包装值，但这不是惯用的:

Alternately, return a rejected promise with an Error wrapping the value, but it's not idiomatic:

} catch (error) {
    return Promise.reject(new Error(400));
}

(或者只是return Promise.reject(400);，但同样，没有上下文信息.)

(Or just return Promise.reject(400);, but again, then there's no context information.)

在你的情况下，当你使用 TypeScript 并且 foo 的返回值是 Promise，你会使用这个:

In your case, as you're using TypeScript and foo's return value is Promise<A>, you'd use this:

return Promise.reject<A>(400 /*or Error*/ );

在 async/await 的情况下，最后一个可能有点语义不匹配，但它确实有效.

In an async/await situation, that last is probably a bit of a semantic mis-match, but it does work.

如果你抛出一个 Error，那么对于任何使用 await 语法消耗你的 foo 的结果的东西来说都很好:

If you throw an Error, that plays well with anything consuming your foo's result with await syntax:

try {
    await foo();
} catch (error) {
    // Here, `error` would be an `Error` (with stack trace, etc.).
    // Whereas if you used `throw 400`, it would just be `400`.
}

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