async-hooks.js

const express = require('express');
const { AsyncLocalStorage } = require('async_hooks');
const http = require('http');

const asyncLocalStorage = new AsyncLocalStorage();
const app = express();

app.use((req, res, next) => {
    asyncLocalStorage.run({
        seqId: req.query.seqId // Set here
    }, next);
});

// Route handler to count numbers up to 5
app.get('/count-to-five', (req, res) => {
    let count = 1;
    const timer = setInterval(() => {
        const seqId = asyncLocalStorage.getStore().seqId; // Get here
        console.log(`${seqId}: count: ${count}`);

        if (count === 5) {
            clearInterval(timer);
            console.log(`<--- ${seqId}: finished --->`);
            res.send('Counted to 5!');
        }

        count++;
    }, 1000);
});

app.listen(8080, () => {
    console.log('Server is running on port 8080');

    // Test call
    http.get('http://localhost:8080/count-to-five?seqId=FirstInstance');
    http.get('http://localhost:8080/count-to-five?seqId=SecondInstance');
});