Arrow function logic in React Native CLI project

I created a new React Native CLI project and was thinking to convert the App component to a class based component to fix a hot reload issue when using react-navigation.

But I don't understand the logic with these two arrow functions, and how to convert it:

const App: () => React$Node = () => {
  return <NavigationWrapper />;
};

Update: the arrow question has resolved, though it didn´t help for the hot reload issue (a glitch in my logic there). See this link for a solution for that.