With the release of the iPhone X, I've found myself needing to have special conditions in a few of my React Native styles. Below is what I'm using to do that check.

import { Dimensions, Platform } from 'react-native';
export const isIphoneX = () => {
  let d = Dimensions.get('window');
  const { height, width } = d;
  return (
    // This has to be iOS duh
    Platform.OS === 'ios' &&
    // Accounting for the height in either orientation
    (height === 812 || width === 812)
  );
}

That's it! Easy as that.