# fetch() in Run Real JavaScript leaks ~10KB per call (even when the request fails)

**URL:** <https://community.folivora.ai/t/fetch-in-run-real-javascript-leaks-10kb-per-call-even-when-the-request-fails/47966>\
**Category:** Bugs or Unexpected Behavior\
**Created:** [October 6, 2026, 10:57am UTC](https://community.folivora.ai/t/fetch-in-run-real-javascript-leaks-10kb-per-call-even-when-the-request-fails/47966 "2026-10-06T10:57:56Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![bamieh](https://community.folivora.ai/user_avatar/community.folivora.ai/bamieh/32/46925_2.png) [@bamieh](https://community.folivora.ai/u/bamieh)\
**Post date:** [October 6, 2026, 10:57am UTC](https://community.folivora.ai/t/fetch-in-run-real-javascript-leaks-10kb-per-call-even-when-the-request-fails/47966/1 "2026-10-06T10:57:56Z")

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Hey Andreas,

I've been chasing BTT memory creeping up for a few weeks now. I run a couple of long Run Real JavaScript scripts that poll a small local HTTP server, around 1000 requests a minute, and BTT grows by roughly 1.2GB an hour until i restart it. Idle BTT is totally fine, it sat at ~66MB the whole time i watched it.

So I measured each call on its own: 3000 calls in a loop, `footprint -p` before and after, then waited to see if anything came back. Nothing did.

- fetch, tiny response: ~12KB per call
- fetch, 17KB response: ~34KB per call
- fetch, body never read (just `r.status`): ~11KB per call
- fetch to a port with nothing listening: ~10KB per call
- set/get variables, get\_variable\_type, setTimeout, a 0s pause action and webserver reads from outside: basically 0

Easiest repro, no server needed:

```js
async function leak() {
  for (let i = 0; i < 3000; i++) {
    await fetch('http://127.0.0.1:1/').catch(() => null);
  }
  return 'done';
}

```

Run that as a Run Real JavaScript action and BTT goes up ~30MB and stays there.

I think I see why. In the fetch polyfill (`String(fetch)`), `request.onload` is a closure that captures `request`, so the native XMLHttpRequest holds a JS function that points back at itself and I'm guessing JSC can't collect that loop. A plain XMLHttpRequest written the same way leaks the same ~13KB. When I null out `onload`/`onerror` after the request finishes it drops to ~3.5KB per call, but then requests start stalling for seconds at a time, so I don't have a workaround on my end. Probaly needs a fix on the native side.

Setup: BTT 6.885 (build 2026100205), macOS 26.6.2, M4 Pro MacBook Pro. I only tested with the isolated JS context turned off.

Happy to run a test build or grab samples if that helps. Thanks for BTT btw, I use it for pretty much everything.

---

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**Author:** ![Andreas\_Hegenberg](https://community.folivora.ai/user_avatar/community.folivora.ai/andreas_hegenberg/32/39221_2.png) [@Andreas\_Hegenberg](https://community.folivora.ai/u/Andreas_Hegenberg)\
**Post date:** [October 6, 2026, 11:01am UTC](https://community.folivora.ai/t/fetch-in-run-real-javascript-leaks-10kb-per-call-even-when-the-request-fails/47966/2 "2026-10-06T11:01:32Z")

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thanks for reporting, I'll add a small fix for the next build