Async state

Every operation exposes one immutable snapshot:

type AsyncState<Data, Empty = null> = {
  status: "idle" | "loading" | "success" | "error";
  data: Data | Empty;
  error: unknown | null;
  isLoading: boolean;
};

The fields are deliberately separate. A request can keep useful data while reporting an error, and isLoading can remain true while another concurrent request completes.

Lifecycle

By default, failures preserve the previous data. Use dataOnError when a failure should replace it:

const operation = createAsync(loadItems, {
  initialData: [],
  dataOnError: () => [],
});

Immutable snapshots

Snapshots are frozen and replaced as a unit. Consumers can safely compare snapshot references, while adapters can expose each field through their native reactive APIs.