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

Question

我的想法如下：我想同时发送多个请求，而不必等到先前执行。

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();

在此处运行此代码可以按预期在浏览器中运行，但会给出以下使用节点运行的输出：

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)

知道为什么会发生这种情况吗？

请注意，我插入只是sleep为了测试该catch块是否会在第一个请求失败的情况下执行，这不是所需的行为。我想同时发起这些请求，并且我不在乎是否有一个失败。我想稍后检查let result = await Promise.allSettled(executions);哪些请求有效，哪些请求失败。我希望这一点很清楚。

Answer 1

有趣的问题 - 问题是你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创建同步/立即解决/拒绝的承诺。您需要放在await前面failingRequest()，以便被拒绝的承诺被捕获在周围try/catch，但这可能不是您想要的。

相反，你不应该立即“开始”承诺，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

正如预期的那样。