Type alias Reducer<S, A>

Reducer<S, A>: ((state, action) => S)

Type Parameters

S = any

The type of state consumed and produced by this reducer.
A extends Action = AnyAction

The type of actions the reducer can potentially respond to.

Type declaration

- (state, action): S
- A reducer (also called a reducing function) is a function that accepts an accumulation and a value and returns a new accumulation. They are used to reduce a collection of values down to a single value
  
  Reducers are not unique to Redux—they are a fundamental concept in functional programming. Even most non-functional languages, like JavaScript, have a built-in API for reducing. In JavaScript, it's Array.prototype.reduce().
  
  In Redux, the accumulated value is the state object, and the values being accumulated are actions. Reducers calculate a new state given the previous state and an action. They must be pure functions—functions that return the exact same output for given inputs. They should also be free of side-effects. This is what enables exciting features like hot reloading and time travel.
  
  Reducers are the most important concept in Redux.
  
  Do not put API calls into reducers.
  Parameters
  - state: S | undefined
  - action: A
  Returns S

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