Redux

Redux is a predictable state container for JavaScript applications. It was created by Dan Abramov and Andrew Clark and released in 2015. While commonly used with React, Redux is library-agnostic and can be integrated with any UI framework or vanilla JS. It centers on a single store that holds the entire state of the app. The state is read-only and can only be updated by dispatching actions—plain objects that describe what happened. These actions are processed by reducers, pure functions that compute and return a new state given the previous state and the action. The data flow is unidirectional: action is dispatched, the store forwards it to reducers, a new state is produced, and the UI re-renders accordingly.

Core concepts include the store, actions, reducers, and unidirectional data flow. The store preserves the state; actions describe events; reducers compute new states. Immutability is central: reducers should not mutate existing state but return a new object.

Middleware extends Redux to handle side effects and asynchronous logic between dispatch and reducers. Examples are redux-thunk and redux-saga. Store enhancers add features such as developer tools integration.

In React apps, React-Redux provides bindings to read state and dispatch actions from components. Redux Toolkit offers a recommended, opinionated approach that reduces boilerplate and standardizes setup, reducers, and store configuration. The ecosystem also supports persistence, routing, and server-side rendering.

Redux emerged as a simplification of Flux’s concepts and gained widespread adoption in large-scale applications. Critics note boilerplate in early versions, though Redux Toolkit has mitigated this. Redux remains one of the most commonly used state management solutions in JavaScript, with alternatives available for smaller projects.