Reducer (React)
In React, a reducer refers to a function that takes in two arguments, a state value followed by an action, and returns a new state after processing the one provided to it along with the dispatched action.
More details
Here's the general form of a reducer function in React:
function reducer(state, action) {
// Process state depending upon the action,
// and then return a new state.
}state is the state of a React component while action is an object representing an occurred action/event in the app.