ReduxObservable

Redux-observable is a middleware for Redux that enables handling asynchronous actions using RxJS Observables. It allows complex async flows to be expressed as streams of actions, managed by a concept called epics.

An epic is a function that accepts a stream of actions (action$) and the current state (state$), plus an optional dependencies object, and returns a stream of new actions to dispatch. Epics run inside the Redux middleware chain and can compose asynchronous operations with RxJS operators such as map, switchMap, catchError, debounceTime, and withLatestFrom. The action$ stream provides only incoming actions; the epic’s output is automatically dispatched by Redux.

To use redux-observable, you create an epic middleware via createEpicMiddleware, apply it to the store with applyMiddleware, and start epics by running a rootEpic. Multiple epics can be combined with combineEpics. A common pattern is to filter actions with ofType, switch to a new observable when a new action arrives, and emit success or failure actions. Epics can access state$ to read store state and dependencies for services or API clients.

Advantages of this approach include strong composition, built-in support for cancellation and backpressure, and powerful time-based operations, making it well-suited for flows that depend on streams or complex user interactions. Limitations include the learning curve associated with RxJS and the potential for added complexity compared to simpler async patterns; for straightforward async tasks, other patterns like thunks may be easier to adopt.

See also: Redux, RxJS, and related patterns for managing asynchronous actions in frontend applications.