SIGX400 · Subscribed to a destroyed topic#

Dev message

[sigx] Cannot subscribe to destroyed topic "user:updated".

Suggestion

Subscriptions made after destroyTopic()/group.destroy() can never fire. Subscribe before teardown, or create a new topic.

What happened#

Something subscribed to a topic after destroyTopic() — or the owning group's destroy() — had already run.

A destroyed topic has dropped its subscriber list and will never deliver again. SignalX throws rather than accepting the subscription, because a handler that silently never fires is far harder to debug than an error at the call site.

This almost always means a teardown-ordering problem: something outlived the topic it depends on. Common shapes:

  • A component subscribes in onMounted while an ancestor destroys the group during its own teardown.
  • An async callback lands after teardown — the subscribe call was queued before, but ran after.
  • A module-scoped topic was destroyed by a hot reload while a component still holds a reference.

Fix it#

Subscribe while the topic is alive, and tie the subscription's lifetime to the component:

TypeScript 
import { component, onMounted, onUnmounted } from 'sigx';

const Inbox = component(() => {
    onMounted(() => {
        const off = topic.subscribe(handleMessage);
        onUnmounted(off);
    });

    return () => <List />;
});

If the topic legitimately outlives nothing and you're re-entering a fresh lifecycle, create a new topic instead of reviving the old one — destruction is final by design:

TypeScript 
const topic = createTopic<Message>('user:updated');
  • Messaging — topics and groups
  • SIGX401 — creating a topic on a destroyed group