App.tsx

// ... Other imports. Only import 'orientation' in the following line, if you are using TypeScript
import Orientation, { orientation } from 'react-native-orientation';

export default class App extends Component<Props> {
  componentDidMount = () => {
    Orientation.lockToPortrait();
    Orientation.addOrientationListener(this.orientationDidChange);
  };

  componentWillUnmount = () => {
    Orientation.removeOrientationListener(this.orientationDidChange);
  };

  // Again the type declaration 'orientation' is only for TypeScript
  orientationDidChange = (orientation: orientation) => {
    console.log(orientation);
  };
  
  render() {
    // ...
  }
}