express.js

const express = require('express');

const app = express();

const asyncError = (timeout = 500) => new Promise((res, rej) => {
    setTimeout(() => rej(new Error('async error')), timeout);
});

app.get('/', async () => {
    await asyncError();
});

// should be 

// app.get('/', async (req, res, next) => {
//     try {
//         await asyncError();
//     } catch (err) {
//         next(err);
//     }
// });

app.use((err, req, res, next) => {
    res.status(503);
    res.end();
});

app.listen(8080);