express-response-errors.js

const express = require('express');
const app = express();
const port = 3000;

const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms));

app.use((req, res, next) => {
    const handler = (event, ...args) => {
        console.log(`got ${event} (${req.res?.destroyed})`, args);

        // handle only the first event that comes in
        // for (const k in handlers) {
        //     res.removeListener(k, handlers[k]);
        // }
        // console.log(`cleaned up and done ${event}`);
    };

    const handlers = {
        close: handler.bind(null, 'close'),
        finish: handler.bind(null, 'finish'),
        error: handler.bind(null, 'error'),
    };

    res.once('close', handlers.close);
    res.once('finish', handlers.finish);
    res.once('error', handlers.error);

    // next(err) does not trigger res "error"
    next();
})

app.get('/', async (req, res) => {
    console.log('=> GET /');
    await sleep(5000);

    // does not trigger res "error"
    // throw new Error('qdwqdw');

    // does not trigger res "error" (but res.socket "error" - yes)
    // res.destroy(new Error('dqdwwqd'));

    console.log('<= GET /');
    res.status(200).json({ ok: true });
})

app.listen(port, '0.0.0.0', () => {
    console.log(`listening on ${port}`);
});