在try/catch块中等待两个promise将导致“未处理的promise拒绝”[重复]

Question

null

async function testMultipleAwait() {
  try {
    const aPromise = new Promise((resolve) => {
      setTimeout(() => resolve('a'), 200);
    });

    const bPromise = new Promise((_, reject) => {
      setTimeout(() => reject('b'), 100);
    });

    const a = await aPromise;
    const b = await bPromise;
  } catch (e) {
    console.log('Caught error', e);
  }
}

testMultipleAwait();

不会导致“捕获错误”输出，相反，我得到

tsc test-try-catch-await.ts && node test-try-catch-await.js

(node:31755) UnhandledPromiseRejectionWarning: b
(node:31755) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:31755) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
Caught error b
(node:31755) PromiseRejectionHandledWarning: Promise rejection was handled asynchronously (rejection id: 1)

Answer 1

我想我知道问题出在哪里了。即使promise以并发方式启动，您仍然在依次等待apromise和bpromise:

const a = await aPromise; // First await this...
const b = await bPromise; // and then start to await this

当两个promise都实现时，这就不是什么问题了。它会让jou等待promise的时间。所有都会等待，然后愉快地继续。这就是为什么这个问题一点都不那么明显...

重要的是要知道，由于异步/等待，这个try-catch在幕后被转换为promise。这意味着首先等待的the语句之后的任何内容都将在promise.then回调函数中结束。

tsc test-try-catch-await.ts && node test-try-catch-await.js

1 first node sees the error     > (node:31755) UnhandledPromiseRejectionWarning: b
2                                 (node:31755) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
3                                 (node:31755) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
4 and then your catch handler   >      Caught error b
5                                 (node:31755) PromiseRejectionHandledWarning: Promise rejection was handled asynchronously (rejection id: 1)

PromiseRejectionHandledWarning: Promise rejection was handled asynchronously.

一旦微任务队列为空，就会抛出拒绝错误。

promise拒绝已经处理，但是node认为您太晚了。您可以使用promise.all来解决此问题。这样，您等待一次，您的异步函数将首先捕获每个潜在的错误。

// Everything just as it is.. and then:

const [a, b] = await Promise.all([
    aPromise, 
    bPromise,
]);

因为我很好奇，我在chrome控制台中输入了您的代码，看看会发生什么。错误日志会弹出一个非常短的时间（我猜是100ms)。看着这个输出，你可以听到chrome说：