feat: add `getAbortSignal()` #16266

Rich-Harris · 2025-06-30T14:41:11Z

This extracts getAbortSignal() from #15844, since it is (at least theoretically) independently useful and is easier to review in isolation.

It may prove necessary to expose STALE_REACTION in some form, so that people can do signal.reason === ??? inside a .catch handler to determine whether or not to rethrow an error. But rather than get bogged down in design questions around what it should be called and where it should be exported from, I think we can safely cross that bridge later if we need to.

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changeset-bot · 2025-06-30T14:41:15Z

🦋 Changeset detected

Latest commit: 1b5857f

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

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svelte-docs-bot · 2025-06-30T14:41:40Z

Preview: https://svelte-dev-git-preview-svelte-16266-svelte.vercel.app/

github-actions · 2025-06-30T14:42:56Z

Playground

pnpm add https://pkg.pr.new/svelte@16266

Ocean-OS · 2025-06-30T15:18:19Z

what if instead of aborting and passing a symbol, we passed an object with { stale: boolean }?

Rich-Harris · 2025-06-30T15:24:13Z

Ah so you'd do something like this?

promise.catch((error) => {
  if (error.stale) return;
  throw error;
});

That could be nice and simple.

Separately: not sure why the tests are failing in CI but not locally. Guess I'll try bumping the timeout

packages/svelte/src/index-server.js

elliott-with-the-longest-name-on-github · 2025-06-30T18:44:30Z

packages/svelte/src/internal/client/constants.js

@@ -27,6 +27,9 @@ export const LEGACY_PROPS = Symbol('legacy props');
 export const LOADING_ATTR_SYMBOL = Symbol('');
 export const PROXY_PATH_SYMBOL = Symbol('proxy path');

+// allow users to ignore aborted signal errors if `reason.stale`
+export const STALE_REACTION = { stale: true };


I like this but I think it needs some refinement... right now refined users of the best typed systems would have to do something like this:

promise.catch(e => { if (typeof e === 'object' && Object.hasOwn(e, 'stale') && e.stale === true) { // stuff } })

We either need to export an isStaleReactionAbortError helper that does this and types it correctly or change tact. I would also think about making this a class extending Error as right now it would fail an if (e instanceof Error) check which is always a bad feeling when catching an error...

hmm. this is exactly the rabbit hole I wanted to avoid. my hunch/hope is that there will be vanishingly few situations where you actually need to do this check, and so my thinking was that we can punt on this for now (while adhering to reason.stale being true if we do make it an error in future)

just don't want #15844 to be held up by unnecessary bikeshedding

I would be fine punting on any type-related stuff but changing this to an error instance seems kinda essential, throwing non-Errors in any context where you expect users to catch them seems... bad

elliott-with-the-longest-name-on-github · 2025-06-30T19:18:33Z

packages/svelte/src/internal/client/constants.js

@@ -27,6 +27,12 @@ export const LEGACY_PROPS = Symbol('legacy props');
 export const LOADING_ATTR_SYMBOL = Symbol('');
 export const PROXY_PATH_SYMBOL = Symbol('proxy path');

+// allow users to ignore aborted signal errors if `reason.stale`
+export const STALE_REACTION = new (class StaleReactionError extends Error {


nasty. effective. love it

elliott-with-the-longest-name-on-github · 2025-06-30T19:19:57Z

packages/svelte/src/internal/client/runtime.js

+	if (reaction.ac !== null) {
+		reaction.ac?.abort(STALE_REACTION);
+		reaction.ac = null;
+	}


Suggested change

if (reaction.ac !== null) {

reaction.ac?.abort(STALE_REACTION);

reaction.ac = null;

}

reaction.ac?.abort(STALE_REACTION);

reaction.ac = null;

I don't think the check is buying us anything here right?

it's saving us from writing reaction.ac, which is more expensive than reading it. though it doesn't need to be optional

packages/svelte/src/internal/server/abort-signal.js

elliott-with-the-longest-name-on-github

just a couple of nits but lgtm now

Co-authored-by: Elliott Johnson <sejohnson@torchcloudconsulting.com>

gyzerok · 2025-07-02T07:19:20Z

Thats an amazing feature, great work! We will put it to a great use in our project.

Another interesting possbile use is to pass a single AbortController to all the event subscriptions, to be able to cancel them all on component destraction.

node.addEventListener('something', { signal: getAbortSignal() })

webJose · 2025-07-02T16:02:18Z

Can't find the docs of getAbortSignal @ https://svelte.dev, or at least the search doesn't pick up on it.

Ocean-OS · 2025-07-02T19:22:15Z

Just merged a PR to update the docs, so it should be updated shortly.

Thiagolino8 · 2025-07-02T20:37:30Z

Just merged a PR to update the docs, so it should be updated shortly.

The getAbortSignal docs have code for async svelte
Which is, at the moment, invalid

Rich-Harris added 5 commits June 30, 2025 09:10

WIP getAbortSignal

bc10186

add test

edec6cd

regenerate

c6b475c

add error code

a1250ed

changeset

d754aad

regenerate

02835be

Rich-Harris added 4 commits June 30, 2025 11:24

try this

57144a0

{ stale: true }

480f55d

fix test

f0aac15

lint

c4a948d

elliott-with-the-longest-name-on-github reviewed Jun 30, 2025

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packages/svelte/src/index-server.js Outdated Show resolved Hide resolved

abort synchronously in SSR

9312594

elliott-with-the-longest-name-on-github reviewed Jun 30, 2025

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make STALE_REACTION a StaleReactionError extends Error

5e056cd

elliott-with-the-longest-name-on-github reviewed Jun 30, 2025

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packages/svelte/src/internal/server/abort-signal.js Outdated Show resolved Hide resolved

elliott-with-the-longest-name-on-github approved these changes Jun 30, 2025

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Rich-Harris and others added 2 commits June 30, 2025 15:25

make non-optional

61c0eaa

Update packages/svelte/src/internal/server/abort-signal.js

1b5857f

Co-authored-by: Elliott Johnson <sejohnson@torchcloudconsulting.com>

Rich-Harris merged commit b673145 into main Jun 30, 2025
7 of 14 checks passed

Rich-Harris deleted the get-abort-signal branch June 30, 2025 19:47

github-actions bot mentioned this pull request Jul 1, 2025

Version Packages #16276

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feat: add getAbortSignal() #16266

feat: add getAbortSignal() #16266

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Rich-Harris commented Jun 30, 2025

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feat: add `getAbortSignal()` #16266

feat: add `getAbortSignal()` #16266

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