Reducers are functions that take two arguments: the current state and the action to return a new state result. To put it another way, (state, action) = newState.
Depending on the action, this function determines what the state should contain. It returns an object, which is subsequently used to alter or replace the state.
Introduction. A reducer is a pure function in Redux that accepts an action and the application's previous state and returns the new state. The action specifies what occurred, and the reducer's role is to return the new state as a result of that action.
Multiple slice reducers can respond to the same action, updating their own slice as needed, and then combining the modified slices into the new state object.