Reducer is a fundamental concept in Redux architecture and is a JavaScript function used to update the state of the Redux store. Redux manages the application’s state in a single JavaScript object, which is stored within a structure called the store. Reducers are functions used to update the state of this store.
A reducer takes two parameters: the current state and an action. Based on these parameters, the reducer returns a new state. Redux uses this returned new state to update the state in the store.
Reducers should be designed as pure and side-effect-free functions. This means that reducers should not interact with the outside world and should always produce the same output based on the same inputs (current state and action).
Typically, multiple reducers are used in a Redux application, and these reducers are used to manage specific pieces of state slice. This allows changes to the application state to be focused on specific areas, making code management and maintenance easier.
Reducers are one of the fundamental principles of Redux and play an important role in managing state when using Redux.