@vanya2h/utils-rxjs-react

React bindings for RxJS — hooks and components for consuming Observable<T> / BehaviorSubject<T> in React without boilerplate.

Why

The main benefit is late unwrapping. Instead of subscribing at the top of the tree and threading the resolved value through props, pass the Observable<T> down and let it unwrap at the leaf that actually renders it. Re-renders stay scoped to the components that consume the value — parents and siblings don't repaint when the data changes. In practice this turns "everything re-renders when the store updates" into "only the cell that reads this field re-renders," which adds up across a real-world React app.

Install

pnpm add @vanya2h/utils-rxjs-react react rxjs

Peer deps: react ^18 || ^19, rxjs ^7.

API

useObservable(observable$, initialValue)

Concurrent-safe subscription built on useSyncExternalStore. Returns initialValue until the first emission, then the latest emitted value. Single subscription per mount; re-subscribes when the observable identity changes.

const count = useObservable(count$, 0);

usePending(source$, getDefaultValue?)

Wraps any ObservableLike<T> (an Observable<T> or a plain T) into a { status: "pending" | "fulfilled" | "rejected" } state machine. The rejected shape exposes onReload for retry.

const status = usePending(user$);

if (status.status === "pending") return <Spinner />;
if (status.status === "rejected") {
  return <button onClick={status.onReload}>Retry</button>;
}
return <div>{status.value.name}</div>;

<Pending value$={...}>

Component sugar over usePending. Picks one of the pending / rejected / children render-props based on the current status.

<Pending
  value$={user$}
  pending={<Spinner />}
  rejected={({ error, onReload }) => <ErrorView error={error} onRetry={onReload} />}
>
  {(user) => <UserCard user={user} />}
</Pending>

<BehaviorSubjectRender value$={...}>

Subscribes to a BehaviorSubject<T> and re-renders children with the latest value. Skips the initial buffered emission (already used as initial state) and deduplicates with distinctUntilChanged.

<BehaviorSubjectRender value$={counter$}>
  {(n) => <span>{n}</span>}
</BehaviorSubjectRender>

<OnlyIfTruthy value$={...}>

Renders the child only when the resolved value is truthy. The render-prop receives the value narrowed to TruthyTypesOf<T>.

<OnlyIfTruthy value$={maybeUser$}>
  {(user) => <UserCard user={user} />}
</OnlyIfTruthy>

render(data, renderable)

Low-level helper used by the components above: invokes a function renderable with data, or returns the static ReactNode.