[prashantg-pixi]

Before submitting the PR, please make sure you do the following

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• Prefix your PR title with feat:, fix:, chore:, or docs:.
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.
• If this PR changes code within packages/svelte/src, add a changeset (npx changeset).

Tests and linting

• Run the tests with pnpm test and lint the project with pnpm lint

---

Problem

Tween.set() (in packages/svelte/src/motion/tweened.js) aborts the previous task when interrupted by a new set() call, but never clears the previous_task closure variable afterward. Each new set() call's rAF loop closure retains a reference to the previous (already-aborted) task — and transitively, the entire chain of prior tasks — so on any long-lived or frequently-interrupted Tween, memory grows unbounded across interruptions and is never released.

No linked issue — new issue creation is currently restricted on this repo for my account, so filing the details directly here instead.

Repro

import { Tween } from 'svelte/motion';
const t = new Tween(new Array(10_000).fill(0));
setInterval(() => t.set(new Array(10_000).fill(Math.random())), 20);

Chrome DevTools heap snapshots taken across repeated intervals show a steadily growing retainer chain rooted at {promise, abort} → previous_task, never released between GC passes.

Fix

One-line fix: null the previous_task reference immediately after aborting it, inside the !started branch of the rAF loop:

 previous_task?.abort();
+previous_task = null;

This mirrors the identical pattern already present in the deprecated tweened() store further up in the same file:

if (previous_task) {
  previous_task.abort();
  previous_task = null;
}

It appears this line was dropped when the newer Tween class was written. previous_task is not read anywhere else after this point in the closure, so this change has no effect on control flow — it only releases a reference that was never used again.

Verification

• Confirmed via Chrome DevTools heap snapshot diffing across many rounds of interrupted tweens in a real-world app: the previous_task retainer chain is fully eliminated post-fix, with allocation/collection back in balance.
• No change to existing abort()/resolve/reject semantics — the fix only clears a variable, it doesn't alter when or how tasks are aborted.
• pnpm test: 7558 passed, 154 skipped. One unrelated failure in runtime-browser/test.ts due to a missing local Playwright browser binary (environment-only, not present in CI).
• pnpm lint: clean.

Happy to add a regression test if maintainers can point me to the right pattern under packages/svelte/tests/motion — didn't want to guess at the existing test conventions for this file.

[pkg-svelte-dev]

Install the latest version of svelte from f22eac4:

pnpm add https://pkg.svelte.dev/svelte/c/f22eac4dba89cfe83c6e4a584ec054dfd3ddc292

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/svelte/pr/18541

Note

This PR is from a fork. A maintainer must approve approve each commit before it can be built and installed.

[changeset-bot]

🦋 Changeset detected

Latest commit: f22eac4

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
svelte	Patch

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