Promises don’t cancel.
That’s the cold fact staring down every JavaScript dev who’s ever tried to abort a fetch mid-flight or kill a timeout gone rogue. Inngest’s latest blog — “You can’t cancel a JavaScript promise (except sometimes you can)” — lays it bare: native Promises, baked into ES6 since 2015, lack a built-in kill switch. No .cancel() method. No magic stop button. You fire them off, and they’re yours forever, resolving or rejecting on their own sweet time. Market data backs this: Stack Overflow’s 2023 survey shows 68% of pros wrestling with async flows daily, yet cancellation woes pop up in 22% of GitHub issues tagged ‘async’. It’s not hype; it’s a structural flaw in the language’s control flow.
Why JavaScript Promises Defy Cancellation
Look, Promises were designed for fire-and-forget. Chain ‘em with .then(), handle errors in .catch(), and voilà — predictable async. But cancel? Nope. The spec says once settled (resolved or rejected), that’s it. Unsettled ones? They hang, potentially leaking memory, hogging threads, wasting API calls. Inngest calls these “hanging promises,” perfect for serverless where costs spike on unfinished work.
Here’s a killer quote from their post:
“Promises are fundamentally uncancelable. There’s no way to make a pending Promise reject or resolve from the outside. It’s a core part of their design — they’re built to represent a value that will exist in the future, no matter what.”
Spot on. And it’s bitten big players: Netflix’s Falcor library danced around it; React Query layers AbortController on top. Usage stats? npm downloads for ‘p-cancel’ (a hacky wrapper) hit 1.2M weekly. Devs crave control.
But — and this is my sharp take — Inngest’s spin feels like PR gloss. They’re pitching their durable functions as the fix, where steps can pause/resume sans hanging promises. Fair, but it’s not revolutionary; it’s repackaging AbortSignals with workflow orchestration. Remember Node 15’s AbortController? That should’ve been the endgame.
Can You Actually Cancel a JavaScript Promise?
Yes. Sort of. Enter AbortController — the 2017 hero nobody asked for but everyone needs. Pass an AbortSignal to fetch(), timers, whatever. Call abort(), and it throws AbortError. Boom, pseudo-cancellation.
const controller = new AbortController();
fetch('/api/data', { signal: controller.signal })
.then(...)
.catch(err => {
if (err.name === 'AbortError') console.log('Canceled!');
});
controller.abort(); // Kills it
Works for 80% of cases. Market adoption? Chrome 74+, Node 15+. But caveats abound. Custom promises? You gotta wire the signal manually — no auto-magic. And generators, loops? They ignore it unless you check signal.aborted in a tight loop. CPU spinner.
Historical parallel: XMLHttpRequest in the IE6 era. Devs hacked .abort() for years before fetch standardized it. Promises? We’re mid-hack phase. TC39’s been sniffing around cancellation tokens since 2020 proposals fizzled. Prediction: By 2026, native Promise.cancel() lands, spurred by WebGPU’s async explosion — where uncanceled shaders could melt GPUs.
Short para for punch: Hacks rule today.
Deeper dive — Node’s event loop starves on hanging promises. Picture 10K concurrent fetches in a Lambda; half abort, half hang. AWS bills skyrocket. Vercel data (2024 report) flags this in 15% of cold starts. Inngest sidesteps with step functions — exec one step, pause, resume later. Smart for workflows, but overkill for simple UIs.
Why Does Promise Cancellation Haunt Production Code?
Scale it up. E-commerce sites lose $2B yearly to zombie requests (Forrester, 2023). Think user search-abandon: query fires, they bail, server churns. Promises exacerbate. RxJS observables cancel natively — 40% enterprise adoption per State of JS 2023. Why not Promises?
Critique time: Inngest’s blog nods to AbortController but pushes their stack hard. “Hanging promises for control flow” sounds clever, but it’s admitting Promises fail at coordination. Their E2E tests? Flawless resumption. Real-world? Network flakes, auth expires — edge cases galore.
One-word verdict: Messy.
And here’s the asymmetry: most libs (Axios, TanStack Query) wrap AbortController now. Raw Promises? Legacy trap. Migrate or perish.
Table stakes for 2024: signal everywhere. But teach juniors wrong, and you’re shipping bugs.
🧬 Related Insights
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- Read more: Running LLMs on Kubernetes? Your Infrastructure Doesn’t Protect You From Prompt Injection
Frequently Asked Questions
What does a hanging promise mean in JavaScript?
A pending Promise that never settles — leaks resources, blocks flows.
How do you cancel a JavaScript promise?
Use AbortController’s signal in fetch/timers; manually propagate in custom async.
Is Inngest’s approach to promises worth it?
Great for durable workflows; overkill for client-side apps.
