preview.js

if (isChromatic() && document.fonts) {
  addDecorator(story => {
    const [isLoadingFonts, setIsLoadingFonts] = useState(true);
    useEffect(() => {
      Promise.all([
        document.fonts.load('400 1em Untitled Sans'),
        document.fonts.load('italic 400 1em Untitled Sans'),
        document.fonts.load('500 1em Untitled Sans'),
        document.fonts.load('italic 500 1em Untitled Sans'),
      ]).then(() => setIsLoadingFonts(false));
    }, []);

    return isLoadingFonts ? null : story();
  });
}