State Reducer

Definitions

1. A pure function that takes the current state and an action object, then returns a new state without mutating the original. Reducers are the core update mechanism in Redux-style architectures, and the pattern derives from Array.prototype.reduce.

   In plain English: A function that looks at what happened (the action) and the current data, then produces a fresh, updated copy of that data.

   Example: "The cart reducer handles ADD_ITEM by spreading the old state and appending the new product — no mutation allowed."

Related Terms

• Action
• Algebraic Data Type
• Category
• Closure
• Computation Expression
• Redux Saga
• Side Effect
• State Container
• Thunk