# useSource

Observes an Effect, Stream, Fx, or value after mount. A Svelte source store or
runtime store can replace the producer; the previous scope closes first.
Server rendering reads only `initial`, and never starts application effects.

## Signatures

```ts
export declare function useSource<A, E = never, R = never, ER = never>(source: Source<A, E, R> | Readable<Source<A, E, R>>, options?: SourceOptions<A, E, R, ER>): AsyncState<A, E | ER>;
```