javascript - 我使用 .catch 来捕获 promise 的拒绝，但它说我使用 .catch

Question

我有一堆代码。该代码具有异步功能，即 Promise。我在 try...catch 里等待我的 promise 。如果有错误，我会真诚地拒绝。看到这个，

runService(options.target, options, socket)
    .then(async id => {
        if(user) {
            .
            .
            .
    })
    .catch(error => {
        console.log('Here', error);
        return socket.emit('error', error);
    });

runService 的功能如下，

const startService = (target, options, socket) => {
    return new Promise(async (resolve, reject) => {
        target = typeof(target) == 'string' && target.trim() != '' ? target.trim() : false;
        if(target) {
            try {
                let addresses = await dns.promises.lookup(url.parse(target).hostname, 4);
            } catch(exception) {
                return reject(exception);
            }
            const id = await createHash(32);
            const targetSlug = url.parse(target).hostname.split('www.').reverse()[0].replace(/[-.]/g, '');
            const date = new Date();
            socket.emit('log', { stage: 1, message: 'Starting simulation and analysis process' });
            const chrome = await launchChrome([
                `--window-size=${options.fullscan ? 1920 : options.desktopResolution.width},${options.fullscan ? 1080 : options.desktopResolution.height}`,
                '--disable-background-networking',
                '--disable-sync',
                '--disable-default-apps',
                '--no-first-run',
                '--enable-automation',
                '--disable-translate',
                '--disable-extensions',
                '--mute-audio',
                '--no-sandbox',
                headless ? '--headless' : ''
            ]);
    .
    .
    .
    });
};

我正在使用 try...catch 并调用该函数，因为它会准确地抛出异常，

let addresses = await dns.promises.lookup(url.parse(target).hostname, 4);

它抛出并 UnhandledPromiseRejectionWarning输出是这样的；

Output http://prntscr.com/mf60hr

为什么会有UnhandledPromiseRejectionWarning它不会调用 socket.emit('error', error)上线.catch()堵塞。这是为什么？

Answer 1

避免 Promise constructor antipattern ，和never pass an async function as the executor to new Promise !你应该只写

async function startService(target, options, socket) => {
    target = typeof(target) == 'string' && target.trim() != '' ? target.trim() : false;
    if(target) {
        // try {
            let addresses = await dns.promises.lookup(url.parse(target).hostname, 4);
        // } catch(exception) {
        //    throw exception;
        // }
        // well this `try`/`catch` is pointless, just drop it
        const id = await createHash(32);
        const targetSlug = url.parse(target).hostname.split('www.').reverse()[0].replace(/[-.]/g, '');
        const date = new Date();
        socket.emit('log', { stage: 1, message: 'Starting simulation and analysis process' });
        …
    }
}