Only a basic navigation reducer

basicNavigationReducer.js

// Don not forget to check the complete code here ---> https://github.com/shubhnik/redux-react-navigation
// The particular navigationReducer here ---> https://github.com/shubhnik/redux-react-navigation/blob/master/src/Reducers/navigationReducer.js
const AppNavigator = StackNavigator({
  screen1: {
    screen: Screen1
  },
  screen2: {
    screen: Screen2
  }
});

// We set the initial state of the navigator to route "screen1", i.e screen1 will be displayed first.
const initialState = AppNavigator.router.getStateForAction(AppNavigator.router.getActionForPathAndParams('screen1'))
const navigationReducer = (state = initialState, action) => {
  
    // **action**  will be of type: {"type": "Navigation/NAVIGATE", "routeName": SOME_ROUTE}
    // gets the new updated state of the navigator (previous state + new route), will return null if the action is not understandable.
    const newState = AppNavigator.router.getStateForAction(action, state)
    
    // return newState or previous state if newState is null
    return newState || state;
}