Interacting with server in listen callback

[mike-fam]

I'm trying to interact with the server in the listen callback.

const app = express()
const server = createServer(app);

app.use(express.static('public'));

server.listen(4400, () => {
	console.log('listening');
	spawnSync('curl', ['127.0.0.1:4400'], { stdio: 'inherit' });
	console.log('finish curl');
	server.close();
});

Here's the output:

listening

and it just hangs in there forever. I'm expecting it to print out the curl output and then stop the script, but the server seems to be not ready for some reason. This also happens with other tools too and not just curl (curl is just my testing tool here). When I run curl localhost:4400 in the terminal, it works fine. What could be the reason that I can't interact with the server in the listen callback?