来自NodeJS的神秘未处理promise警告[副本]

Question

当下面的代码错误(ping()拒绝其promise）时，我会收到警告。HTTP函数似乎错误很好。我想，ping()本身一定发生了什么事情，这在某种程度上避免了try-catch。

有人能开导我吗？（这是在几次尝试改变事情以使其工作之后。）

(async () => {
    try {
            let webTask, pingTask;

            try {
                    webTask = httpsGet(urls[0]);
            } catch (e) {
                    console.log(e);
            }

            try {
                    pingTask = ping('8.8.8.8');
            } catch (e) {
                    console.log(e);
            }

            try {
                    const webResult = await webTask;
                    console.log('HTTP result:', webResult);
            } catch (e) {
                    console.log(e);
            }

            try {
                    const pingResult = await pingTask;
                    console.log('Ping result:', pingResult);
            } catch (e) {
                    console.log(e);
            }
    } catch (e) {
            console.log('Error:', e);
    }
})();

"main.js" 137 lines, 2945 characters
(node:58299) UnhandledPromiseRejectionWarning: #<Object>
(node:58299) 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:58299) [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.

const netping = require('net-ping');
const pingSession = netping.createSession({
    retries: 0,
    timeout: 10000
});

const ping = ip => {
    return new Promise((resolve, reject) => {
            let result = { ipAddress: ip, start: new Date(Date.now()), end: null, error: null, duration_ms: -1 };

            pingSession.pingHost(ip, (error, target) => {
                    result.end = new Date(Date.now());
                    result.duration_ms = result.end - result.start;
                    if (error) {
                            result.error = error;
console.log('rejecting promise');
                            reject(result);
                    } else {
                            resolve(result);
console.log('resolving promise');
                    }
            });
    });
};

NodeJS 11.13.0

Answer 1

await是javascript构造，它将拒绝promise转换为异常。也就是说，await是处理拒绝的构造。

当你写：

try {
    pingTask = ping('8.8.8.8');
} catch (e) {
    console.log(e);
}

这里没有await，因此没有任何东西可以将拒绝转换为异常，或者以任何方式处理拒绝。

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

const test = (ms, msg) => {
    return new Promise((resolve, reject) => {
        sleep(ms).then(reject(msg)).catch(console.log);
    });
};

(async () => {
    let task1;

    try {
        const ms = 50;
        task1 = test(ms, "hey");
        await sleep(ms * 2); // otherwise you don't get an error
        await task1;
    } catch (e) {
        console.log(e);
    }
})().then(console.log).catch(console.log);

promise()构造函数开始运行test()，50毫秒后promise被拒绝，但是没有任何东西可以将拒绝转换为异常。如果我们删除100 ms的睡眠，那么await在50 ms睡眠完成之前将其“convert rejection to exception”逻辑注册到promise方式，因此当promise在调用await后49 ms被拒绝时，有一个处理程序将其转换为异常。