Router.js

import { createAppContainer, createStackNavigator } from 'react-navigation'
import HomeScreen from './components/HomeScreen'
import DetailsScreen from './components/DetailsScreen'

const AppNavigator = createStackNavigator({
  Home: {
    screen: HomeScreen,
  },
  Details: {
    screen: DetailsScreen,
  },
}, {
    initialRouteName: 'Home',
});

export default createAppContainer(AppNavigator)