Promise.allSettled 和 try/catch 未处理的承诺拒绝

Question

我的思路是这样的：我想同时发送多个请求，而不必等到先验执行。

所以我的伪代码如下所示：

function sleep(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

function failingRequest(){
    return new Promise((resolve, reject) => {
        reject('Request failed');
    });
}

function successRequest(){
    return new Promise((resolve, reject) => {
        resolve('Request success');
    });
}

async function main() {
    try {
        let executions = [];
        executions.push(failingRequest());
        await sleep(4000);
        executions.push(successRequest());
        let result = await Promise.allSettled(executions);
        console.log(result);
    } catch (err) {
        console.log('Outer error occured.');
        console.log(err.message);
    }

    console.log('done');
}
main();

运行此代码在浏览器中按预期工作，但给出以下输出运行节点：

node:761) UnhandledPromiseRejectionWarning: Request failed
api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:761) [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 exi not handled will terminate the Node.js process with a non-zero exit code.
[
  { status: 'rejected', reason: 'Request failed' },
  { status: 'fulfilled', value: 'Request success' }
]
done
(node:761) PromiseRejectionHandledWarning: Promise rejection was handled asynchronously (rejection id: 1)

知道为什么会这样吗？

请注意，我只插入了 sleep，这样我就可以测试是否会在第一个请求失败时执行 catch 块 这不是预期的行为。我想同时发起这些请求，我不在乎一个是否失败。我想稍后使用 let result = await Promise.allSettled(executions); 检查哪些请求有效，哪些请求失败。我希望这是清楚的。

Answer 1

有趣的问题 - 问题是您实际上并没有模拟异步请求。事实上，您的两个请求方法只是在创建 resolved/rejected synchronously/immediately 的承诺。您需要将 await 放在 failingRequest() 之前，以便将被拒绝的承诺包含在周围 try/catch 中，但这可能不是您想要的。

相反，你不应该立即“启动”promise，它应该是这样的：

try {
        let executions = [];
        executions.push(failingRequest);
        await sleep(4000);
        executions.push(successRequest);
        let result = await Promise.allSettled(executions.map(promiseFn => promiseFn()));
        console.log(result);
    } catch (err) {
        console.log('Outer error occured.');
        console.log(err.message);
    }

这将记录

[
  { status: 'rejected', reason: 'Request failed' },
  { status: 'fulfilled', value: 'Request success' }
]
done

符合预期。

Answer 2

Any idea why this is happening?

您创建 failingRequest() 然后等待 4 秒再处理它。

I only inserted sleep so I could test

…因此您导致了未处理的拒绝。删除 await sleep(4000);，它将按预期工作！

Promise.allSettled 和 try/catch 未处理的承诺拒绝

Unhandled promise rejection with Promise.allSettled and try/catch

javascript

try-catch

node.js

promise