What are reducers in Redux?

A reducer in Redux is a function that determines the changes that are done to the state of an application. It implies the action it receives to determine his kind of changes. Redux relies heavily on the reducers that include the state and action of the previous stage to execute the next stage.

The state parameter that is passed on to the reducer function that needs to be the current application state. The update of the state that occurs in the reducer is dependent on the value action.type. If the action.type value present in the action object does not match with the value that is present in the reducer, then the state of default is returned.