I've found a different post on a related topic (How to perform an async operation on exit), but perhaps it doesn't apply to macOS, or just isn't true anymore when running Node.js v14.

My original question was more complicated. I couldn't get setTimeouts or await to work correctly in a callback (or async callback) for SIGINT. But then I realized what I really needed to do, first and foremost, was to be able to catch and ignore SIGINT.

If I could do that, then I could shutdown in response to SIGINT too, if and when I wanted to.

So I went back to basics to see if I could simply disable SIGINT. I couldn't.

I could detect SIGINT, I could respond with console messages or any other synchronous code, but my code was going to shutdown, and shutdown soon, no matter what I did.

process.on('SIGINT', () => { console.log('here'); return false; });
process.on('SIGINT', () => { console.log('here'); return true; });
process.on('SIGINT', () => { console.log('here'); return undefined; });
process.on('SIGINT', () => { console.log('here'); return new Promise(resolve => { console.log(resolve); }); });

None of these approaches prevents my Node.js server from shutting down after hitting Ctrl+C, or otherwise sending a SIGINT to the process.

UPDATE:

When I run my server via node app.js, SIGINT interception is working just like it should!

Apparently I've been being driven crazy by an artifact of running my server app indirectly through nodemon. A Ctrl+C from my IDE's terminal, or an interrupt sent using the IDE's graphical red 🟥 (stop) button can't be properly caught, because the resulting signal is really being sent to nodemon. Outside of the IDE environment, however, without nodemon figuring into things, my graceful shutdown works as I want it to.