Manifesto

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Subscriptions ​

Subscriptions run a listener when a selected Snapshot value changes.

Use observe.state(selector, listener) when UI, logs, scripts, or integrations need to react to published runtime state.

Subscribe to a Slice ​

typescript
const unsubscribe = app.observe.state(
  (snapshot) => snapshot.computed["todoCount"],
  (next, prev) => {
    console.log("Todo count changed:", prev, next);
  },
);

The selector receives each published Snapshot. The listener receives the next and previous selected value.

Seed the Initial Render ​

typescript
render(app.snapshot());

const unsubscribe = app.observe.state(
  (snapshot) => snapshot,
  (snapshot) => render(snapshot),
);

observe.state() observes later publications. Read snapshot() once when you also need the current value immediately.

Clean Up ​

typescript
unsubscribe();
app.dispose();

Unsubscribe when the consumer is gone. Dispose the runtime when the app-owned runtime lifetime ends.

Common Mistake ​

Do not subscribe to the whole snapshot when one field is enough. A focused selector makes update behavior easier to explain.

Next ​

Learn when an action should be visible with Availability, then put the pieces together in Building a Todo App. Read Effects later when the domain needs API, database, model, or queue IO.