mapStateToProps in Redux

The is a function which takes the state as an input parameter and maps the properties in the state to props mapStateToProps  in the component.

mapStateToProps take the state object (the same value returned by a call to store.getState()) as the first argument and return a plain object containing the data that the connected component needs.  This function should be passed as the first argument to connect, and will be called every time when the Redux store state changes.

store in Redux

In Redux store is the state object which holds the Application state. The current state can be accessed using store.getState() and any changes to the state can be performed by dispatching an action to the reducer.

In the previous posts, we saw how to create the store object using createStore and use it to initialize the application. Redux store also allows us to subscribe to events that update the store object. This can be useful to debug changes to the redux store.

In the createStore code of the previous example we will add a subscription to display changes to the state to the console as follows.