examples/with-storybook/stories/4-Font.stories.js

import React, { useEffect, useState } from 'react';
import { storiesOf } from '@storybook/react-native';
import * as Font from 'expo-font';
import { Text } from 'react-native';

export default {
  title: 'Font',
};

export const CustomFontComponent = () => {
  const [loaded, setLoaded] = useState(false);

  useEffect(() => {
    (async () => {
      await Font.loadAsync({
        'retro-regular': require('../assets/retro-regular.ttf')
      });
      setLoaded(true);
    })();
  }, []);

  return (
    loaded && (
      <Text
        style={{
          fontFamily: 'retro-regular',
          backgroundColor: 'transparent',
          fontSize: 56,
          color: '#000'
        }}
      >
        Cool new font
      </Text>
    )
  );
}

// On-Device Register
storiesOf('Font', module).add('Font', () => (<CustomFontComponent/>));