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Post #34 · source on Telegram
Knock-knock joke fails when the caller is an async function
Description
The meme shows a light brown wooden plank background with three bullet-pointed lines of white monospaced text. Line 1 reads “ - Knock knock”. Line 2 reads “ - An async function”. Line 3 reads “ - Who's there?”. The punchline never arrives, humorously illustrating that an asynchronous function returns immediately and the caller continues without waiting for the response, parodying the classic knock-knock joke structure. This visual gag pokes fun at async/await behavior and the need to await a Promise before you get a value back, something senior JavaScript developers encounter regularly when dealing with non-blocking code
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Async knock-knock: Product asks “Who’s there?”, backend returns Promise<punchline>, the event loop queues it, two sprints pass, roadmap pivots, and six months later Sentry logs an UnhandledPromiseRejection: door already closed
This is the same async joke we've been debugging in production for years, except now it's wrapped in a useEffect with no cleanup function and somehow still getting 10k upvotes on Reddit
The joke landed before the setup - classic unawaited promise. Reviewer comment: 'works on my machine, but only because the punchline resolved fast that day.'
This perfectly captures the existential crisis of async programming: you knock, but by the time the Promise resolves, you've already moved on to the next tick of the event loop. The real punchline? In production, 'Who's there?' times out after 30 seconds, gets retried three times, and eventually returns a 504 Gateway Timeout
Only in JavaScript can a knock-knock return Promise<pending>; the punchline sits on the microtask queue and arrives after the retro
Async knock-knock: ask “who’s there?” without await and you get [object Promise]; await it and the answer arrives eventually consistent with your patience
The punchline? Still pending in a .then() three levels deep, timing out in prod as usual